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Reservoir Rock Properties Analysis, Mohsen Masihi Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 1 Sharif University of Technology Reservoir Rock Properties Analysis 2010 Laboratory Work Book No. 26504 Mohsen Masihi Department of Chemical and Petroleum Engineering Sharif University of Technology, Tehran, Iran [email protected]
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Page 1: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 1

Sharif University of Technology

Reservoir Rock Properties

Analysis

2010

Laboratory Work Book No. 26504

Mohsen Masihi

Department of Chemical and Petroleum Engineering

Sharif University of Technology, Tehran, Iran

[email protected]

Page 2: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 2

Table of contents

Course overview ................................................................................................................................ 3

Introduction ....................................................................................................................................... 5

1-Core and plug preparation .............................................................................................................. 6

1-1 Introduction .............................................................................................................................. 6

1-2 Core Slabbing........................................................................................................................... 6

1-3 Plugging using plug drill Press machine ................................................................................... 9

1-4 Trimming Core Plugs ............................................................................................................. 12

1-5 Core gamma logger ................................................................................................................ 15

2-Cleaning and saturation determination .......................................................................................... 24

2-1 Dean Stark ............................................................................................................................. 27

2-2 Retort Oven ............................................................................................................................ 29

2-3 Core Saturator ........................................................................................................................ 32

3-Porosity ........................................................................................................................................ 42

3-1 Hg porometer ......................................................................................................................... 47

3-2 KeyPhi instrument .................................................................................................................. 50

4-Resistivity .................................................................................................................................... 54

4-1 Electrical properties system atmospheric (EPS-A) .................................................................. 55

4-2 Electrical properties system 700 (EPS-700) ............................................................................ 59

5-Surface and interfacial tension ...................................................................................................... 60

5-1 IFT 700 instrument ................................................................................................................. 66

6-Capillary pressure ......................................................................................................................... 77

6-1 CAPRI instrument .................................................................................................................. 78

7-Permeability ................................................................................................................................. 86

7-1 KeyPhi instrument .................................................................................................................. 89

7-2 Benchtop Relative Permeameter (BRP 350) ........................................................................... 89

8- Rock Mechanical Properties ........................................................................................................ 97

8-1 Acoustic Velocity System (AVS 700) ..................................................................................... 97

References and further reading ...................................................................................................... 105

Page 3: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 3

Course overview This course provides an introduction to reservoir rock properties determination by core analysis. Part of

this course introduces the laboratory equipments as well as the procedures used for the core analysis.

Moreover, the theoretical aspects of the parameters used in the core analysis are briefly described.

Hence, the aim of this is to get familiar with of the main rock properties parameters, the way they can

be measured and the sources of errors in the results obtained from the laboratory measurements. At the

end of the course, you will learn what the main properties of rocks are and also you will learn how to

measure them and how to analyze the range of the uncertainty in the results.

These prepared course notes follow closely the sequence of material that will be presented. However,

these are further suggested materials:

1-J. S. Archie and Wall C. G., Petroleum engineering principles and practice. Graham & Trotman,

London, 1986.

2-J. W. Amyx, Bass D. M. and Whiting R. L., Petroleum reservoir engineering (physical properties).

McGraw Hill, Inc., 1988.

3- X. D. Jing, Rock properties course, Imperial College London, 2003

4- M. Masihi, Reservoir Rock Properties course, Sharif University of Technology, 2007.

5-T. Ahmed, Reservoir engineering handbook, Gulf professional publishing, 2001

6- M Ala, Jing, X. D. and Worthington P., Petrophysics course, Imperial College London, 2003

7- M Araujo Fresky, Rock properties, Imperial College London, 2004

Syllabus 1. Core and plug preparation: Introduction to the machines for the various steps of core preparation

including core slabbing, core pluging and trimming. Also sand/shale analysis and depth

matching through the use of core gamma logger will be introduced.

2. Cleaning and saturation determination. The available instruments for core cleaning as well as

saturation determination will be introduced. This includes extraction/distillation method for

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 4

core cleaning (Dean Stark), drying and heating for saturation determination (Retort Oven) and

core saturator for saturation of core before other experiments.

3. Porosity. An introduction to core porosity and various methods of its measurements. Describing Hg

porometer and KeyPhi instruments for porosity measurements.

4. Resistivity. Introduction to the EPS-A instrument for the rock conductivity measurements at surface

pressure and to the EPS-700 at overburden pressure.

5. Surface and interfacial tension. An introduction to various methods of IFT measurements.

Description of IFT700 instrument for measuring IFT.

6. Capillary pressure. Introduction to capillary measurement methods under drainage and imbibition

processes. Description of CAPRI instrument for measuring capillary pressures.

7. Permeability. An introduction to rock permeability. Description of KeyPhi instruments for absolute

permeability measurements and BRP-350 for gas/liquid absolute and relative permeabilities.

8. Rock mechanical Properties. An introduction on how to measure the rock properties like Young’s

modulus and Poisson’s ratio using AVS-700 instrument by application of the sonic waves.

Course structure

The course will consist of approximately 12 sessions (each one 3 hours) of laboratory works including

lectures. The course will be assessed by a final term examination and by laboratory reports.

The notes in some places cover more material than can reasonably be covered during the course and in

other places have deliberate gaps for more discussions. Please fell free to ask questions during the

course.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 5

Introduction Knowledge of the physical properties of the rock and interaction between hydrocarbon system and the

formation rock is crucial in understanding and evaluating the performance of a given reservoir. These

data are usually obtained from two main sources: core analysis and well logging. In this course book

we describe the analysis of cores. A core which is a solid cylinder of rock about 3 inches in diameter

and would usually be about 30 feet long is taken by replacing the drill bit by a “core bit” which is

capable of grinding out and retrieving the heavy cylinder rock. Once the cores are retrieved it is crucial

to properly handle (avoid damaging) and preserve them by avoiding exposure to air. When the core

arrives in the laboratory plugs are usually drilled 20-30 cm apart throughout the reservoir interval. Then

the plugs are analyzed with respect to porosity, permeability, saturation, grain density and lithology.

This analysis, which is performed at high sampling frequency and low cost, is called routine core

analysis. The results from routine core analysis are used in interpretation and evaluation of the

reservoir. Examples are prediction of gas, oil and water production, definition of fluid contacts and

volume in place, definition of completion intervals. There are other important measurements with the

aim of obtaining the detailed information about the multiphase flow behavior. This analysis, which is

performed at low sampling frequency due to high cost and more time due to gathering the data, is

called special core analysis. Special core analysis gives information about the rock wettability, the

distribution of oil, gas, and water in the reservoir (capillary pressure data), residual oil saturation and

multiphase flow characteristics (such as capillary pressure and relative permeability). Measurements of

electrical and acoustic properties, which are mainly used in the interpretation of well logs, are

occasionally included in special core analysis.

The outline of this handout is organized as follows: We first describe the main pre-processing steps that

are considered on the core samples to be prepared before experiments. In chapter two we describe the

core cleaning methods, which are required before core analysis tests, as well as the saturation

determination methods. In the next chapter, the porosity measurement techniques are described and the

instruments available in the laboratory for the determination of the core porosity are described. In

subsequent chapters we then describe the techniques to measure and the available machines to

determine respectively the core sample resistivity, interfacial tension, capillary pressure and

permeability.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 6

1-Core and plug preparation 1-1 Introduction When a piece of rock or a core is wanted to be used for analysis as a sample in the laboratory, several

steps, as per-processing steps, should be considered on the sample to be prepared for experiments. The

main per-processing steps are as follow:

(i) slabbing; the cores need to be slabbed with the aim of making the rock structure visible. This can

simply be done by sawning down the middle of the core and cuting it at desired length.

(ii) plugging: one can drill the plugs at every one foot of the core.

(iii) trimming: both end of the plugs and core samples can be trimmed in order to produce high quality

thin sliced samples without disturbing the structure of the sample.

Moreover, core scanner and core gamma logger may be used for depth matching as well as describing

the core lithology and texture. The detail description of these per-processing steps and the equipments

to do these are described in this section.

1-2 Core Slabbing Core slabbing is the first step in the preparation of samples for core laboratory experiments. The radial

core slabbing saw is a machine for cutting rocks into the smaller parts. This is basically for cutting a

big size outcrop rock into the smaller parts and/or cutting the longer cores to the shorter ones. Radial

core slabbing saw is designed for diamond cutting discs only, which is connected to the motor with a

shaft and two pulleys and the use of the cooling waters improves the slice quality and cutting speed and

reduces the heat which is produced by sawing process. Figure below shows the core slabbing machine

(Fig. 1).

However, students should considered the following safty notices:

1-This machine must only be operated by qualified personnel specially those who has had the

operation training and the safety regulations.

2-Protect yourself from any splash produced by wearing a suitable overall.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 7

Figure 1: Core slabbing machine

Machine Description: The machine has a motor which supplies the rotational motion for sawing. The main machine parts are:

• Radial saw

• Electro motor

• Shaft, pulleys and rim

• Adjustable tilting table

• Cooling system, including pumps, water supply, flexible pipes

The rotational motion transmitted by two pulleys from electro motor. At either side, there are three

different stepped pulley couples. The speed of motion can be adapted by positioning the compound

diamond rim on the suitable stepped pulley couple on the electro motor and saw system. The dimension

of rock sample should be smaller than the max height of saw from table to be cut electively. Bigger

rocks should be broken to a proper part with other methods. One draw back of this machine is its noise.

The machine noise level is around 70 dBa. During the cutting process, the noise level depends on the

material to be cut, the type of disc used, the rotation speed and the cooling.

Page 8: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 8

Experiment operation The procedure for cutting a given sample is as follows:

• If the rock is big then it should first be cut by another method

• Put the sample on the table

• Check the tension on the pulleys

• Adjust the direction of water line on both saw and sample

• Check water tanks and fill them if they are empty

• Start the water pump and check the direction of water and check the flow

• Start the saw by pressing the start bottom

• Cut the sample by screwing up and down of the saw and pushing the sample table of machine

• Press the stop button

• Unclamp the core sample

However, in working with the machine consider the following safety issues: (i) prevent touching of saw

with the machine sample table, because of damaging of saw, (ii) protect yourself from any splash and

water drops by wearing overall and safety glasses.

You should consider the appropriate rotational speed. The motor shaft rotates at 1,440 rpm. When the

belt is on the central pulley either on motor side and disc side, the disc rotates at 1,440 rpm. When the

belt is on the small pulley on motor side and on the large pulley on the disc side, the disc rotated at

2,160 rpm and finally when the belt is on the large pulley on motor side and on the small pulley on the

disc side, the disc rotated at 960 rpm. The schematic diagram of pulleys at both motor side and disc

sides are illustrated in Fig. 2.

Motor 1 440 rpm Spindle disc holder

Figure 2: Pulleys

Cutting linear speed in meters/seconds versus disc diameter and speed are shown in Table 1.

Page 9: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 9

Table 1: Cutting speed and disc diameters of core slabbing machine

Disc diameter

Disc rpm Ø 300 Ø 350 Ø 400 Ø 450 Ø 500

960 15 17.5 20 22.5 25

1440 22.5 26.5 30 34 37.5

2160 34 39.5 45 51 56.5

For cooling of the saw and sample during the operation, water is used. Water is pumped from water

tank and poured directly to the sawing position on the sample. Then, the used water goes to the water

tank. Water tank is composed of to different tank. The recycled water first enters to the first tank, and

after precipitating of cuttings into this tank, the fresh water overflow to the main water tank.

Maintenance Keep the machine clean.

Do not let water and waste in the tray.

Check carefully the v-belt and its strain.

1-3 Plugging using plug drill Press machine The core cutting machine is designed to cut specimens from cores of between 4 to 6 inches, or from

blocks of a similar size. The produced plugs are in two different size of 1 and 1.5 inches. This machine

can be installed on any table (Fig. 3). By screwing down of a hollow plug drill, plugs are cut from the

samples.

However, students should considered the following saftey notices:

-The core cutting machine should only be used by qualified operators who have been suitably trained in

how to produce the quality of cut required under the prescribed safety conditions.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 10

Figure 3: Core plugging machine

Machine Description: The machine can accommodate cores measuring from ½” to 3”. A swivel joint with a tap allows

internal irrigation of the core drill and a hose fitted with a tap allows external irrigation of the core drill.

The speed can be adjusted by repositioning the belt (1800 rpm – 2500 rpm – 3500 rpm) like core

slabbing machine.

The machine comprises of:

• clamping stand

• column

• « Spindle-Motor » unit

• adjustable tilting table

• protective housing

• clamping unit

• recycling tank

Table of machine has a rotating capability up to 45º. This capability causes that user can make plugs

from any part of slab even deviated sides.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 11

Experiment operation • Check the tension on the pulleys

• Check the direction of the spindle

• Fill the recycling tank

• Screw down the core drill and lock it in place

• Mount a core sample and lock it firmly in the clamping unit

• Adjust the lower stop on the core drill. 1-2 mm before the end of slab is sufficient for

prevention of plugging the sample in plug driller. Touching of the driller with table causes

severe damage to the driller.

• Close the core drill protective housing

• Press the Start button

• Open the irrigation taps

• Check the flows

• Cut the core sample

• Press the « Stop » button

• Unclamp the core sample

Speed of rotation can be adjusted by changing pulleys. The procedure for this operation is as:

• open the pulley cover

• loosen the 2 locking screws and pulley tension lever

• pinch together the two sides of the spindle belt

• change the position of the belt

• tighten the belts with the lever and lock the two screws in place

• close the cover

If the tension of pulleys is not sufficient then the belt should be changed. The procedure for changing

the belt is as follow:

• make sure that the machine is disconnected

• open the pulley cover

• loosen the two clamping screws and the belt tensioning lever

• pinch together the two sides of the spindle belt

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 12

• change the belts

• tighten the belts with the lever and lock the two screws

• close the cover

Maintenance • keep the unit and the protective housings clean

• remove debris and core particles

• remove sludge

• clean all moving parts

• change the cooling fluid as soon as it is dirty

• make sure that the machine is disconnected

• remove the pump and the waste pipe from the recycling tank

• empty the tanks

• clean the tanks and the separators

• fill the tank with cooling fluid

• refit the pump and the waste pipe to the recycling tank

1-4 Trimming Core Plugs After preparing plugs in core drill machine, all of them should be cut into desired size. This can be

done by trimming machine. Trimming machine is a bench model designed to produce fast, high quality

thin sliced samples from all materials without disturbing the structure of the sample (Fig. 4).

However, students should considered the following saftey notices:

• Touching any resinous cutting wheel can be dangerous.

• The machine is fitted with safety devices which prevent the wheel from turning when the hood

is open

• This machine must only be used by a qualified person who has received the proper training

required to achieve the quality of cut and the high standard of safety envisaged by the

manufacturer.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 13

Figure 4: Trimming core plug machine

Machine Description: The basic model can work either in manual feed or with an optional hydraulic automatic feed which is

driven by the domestic water supply (Minimum pressure 1.5 bars). In the automatic mode, user can

determine the speed of rotation of saws. The machine consists of two radial saw that can work together

and cut both end of pugs simultaneously. Each cuts needs nearly 0.2 litter cooling water. This machine

is designed to work with all types of cutting wheel (resinous - diamond - boron carbide) and various

accessories and adaptations enable samples or core sections to be cut lengthways. These include cradles

or devices for holding the samples configurations using two wheels which allow parallel-sided sections

of continuous length to be cut in a single operation. The machine is fitted with a safety cut-out switch

which can be reset, or rewound should there be no power, as well as a gradual starting device. When

the cover is open this safety switch open the electric current and the machine don’t work. The use of

passivated water is strongly recommended to avoid corrosion.

Experiment operation The machine can work in both manual and automatic mode. By setting two lever taps on the body of

machine, three situations are achieved. The lever taps allow the wheel (saw) to advance or return.

• quick back mode: in this mode the saws go back quickly and positioned at the start point. This

mode can be achieved by setting both taps down.

Page 14: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 14

• stop manual: in this mode user should handle the position of saws for trimming the plug

manually and can be achieved by setting top tap to up and bottom tap to dawn

• automatic feed: in this situation samples are trimmed automatically by the machine. The

rotational speed of the saws can be adjusted by the “Movement regulator” beside the lever taps.

Manual mode Steps for operating in manual mode are as follows:

• Press the start bottom

• Set the taps to " Quick back " position, at the end of the race, the lever is independent of jack,

• Set the taps to the "Manual stop" position.

• Adjust the direction of water line on saw and sample

• Check water tanks and fill them if they are empty

• Start the water pump and check the direction of water and check the flow

• Close the protective housing of machine

• By moving the saws to front start trimming of the sample

• Press the Start button

• Press the « Stop » button

• Unclamp the core sample

Automatic feed (optional) Steps for operating in automatic feed mode are as follows:

• Press the start bottom

• Set the taps to the " Automatic feed " position

• Adjust the direction of water line on saw and sample

• Check water tanks and fill them if they are empty

• Start the water pump and check the direction of water and check the flow

• Close the protective housing of machine

• Gradually open the movement regulator until the required feed rate is obtained.

• At the end of the cut, turn the taps to the "Rapid return” position.

• Press the « Stop » button

• Unclamp the core sample

Page 15: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 15

Maintenance Apart from keeping the machine properly clean, no specific maintenance is required. Make sure that

any sediment or waste matter is removed from the tank before starting. Change the fluid according to

the frequency of use and its deterioration over time (shelf life).

1-5 Core gamma logger The main purpose for using gamma logger is to correlate the depth of each section of core

with the depth of a log in the formation i.e. depth matching. Gamma rays in rocks arise

primarily from the radioactive decay of elements belonging to the "KUT" radioactive

families for Uranium 238, Thorium 232, and potassium isotope K-40. The Gamma logger

measures both total naturally occurring gamma radiation in core samples in API units, and

the spectral response in weight concentrations of thorium, uranium and potassium.

Machine Description: The core samples are carried over the detector by a motor driven belt conveyor. The conveyor is 15 cm

wide and 3 meters long (belt length is 6 meters). The belt is marked in increments of 0.25 meters to aid

in placement of the core along the belt (Fig. 5). Speed and motion of the conveyor belt are controlled

with a stepper motor drive from the SmartLog software. Belt speed is set in the software as 3 cm/min,

but can be adjusted in Factory Setup.

Figure 5: Natural Gamma Logger

Measurement of the Spectral Log requires much more radiation data to determine the constituents and

hence a slow speed is necessary. Belt travel is synchronized with the gamma-ray data by the software.

The default time period for each scan is 500 seconds during which time the core travels 25 cm at belt

speed of 3cm/min. Thus, one data point is obtained for every 25 cm depth of the core.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 16

The gamma radiation is detected by a 3x3" Sodium Iodide crystal and photomultiplier located below

the belt in the center of the conveyor. The detector is protected from ambient radiation with low

activity virgin lead shielding.

Calibration The process of calibration is as follows:

• Belt speed:

1. From the main APPLILAB screen, set the speed to the minimum value of 0.150 ft/min and

validate with OK.

2. Have a stop watch ready. Start the belt and the stop watch. Once the belt has moved by a

minimum of 1 foot, write down the exact belt displacement and the time elapsed. Repeat these

steps for various speeds e.g. for 0.450 ft/min to the maximum speed of 0.750 ft/min.

3. In the file: C:\AppliLab\Project\NGL200 \GammaLogger.xls, open the tab Calibration.

4. Report the set point, distance and time in related columns (Fig 6). The effective "measure"

speed is calculated in the last column. The graph, the gain and the offset are automatically

updated. Note: if the coefficient R2 is less than 0.9990, repeat the measurement. Save and close

the Excel file.

Figure 6: Illustration of belt speed calibration

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 17

• Probe:

In Fig. 7, gain refers to the probe amplifier gain. The amplifier gain can be adjusted in either automatic

or manual mode. Gain calibration must be refreshed from time to time to fit the probe response drift

with aging.

After a gain calibration, you must calibrate the "zero" (background). Natural radioactivity

(background) is usually of low level, especially apparent background accessible to the probe set in the

lead shield. However, this apparent background is not negligible compared to the natural radioactivity

in core sample. Natural radioactivity (background) depends on various factors such as local geology,

climate (rain, temperature) etc...

Automatic gain calibration:

− Stop the belt if it was moving. Remove any sample and standard U, Th and K from the belt.

− Install the "hot Thorium" standard provided with the equipment on the belt, directly over the

detector in the lead tunnel.

− Double click on the trend area to pop up this window (calibration window). Click on the button

to start the gain automatic determination. The duration is about 3 hours. The calibration time

countdown is displayed in the right top corner.

− At the end of the acquisition, the gain is automatically adjusted to fit the standard.

Figure 7: Illustration of window of gain calibration

Zero calibration:

During zero calibration, the apparent background is scanned during a set time (Standard duration is

set to 10,000s to suit 99% of cases).Then this "zero" spectrum is automatically memorized. During

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 18

next core scan campaign; this "zero" will be automatically subtracted from all the spectrum

measurements. Note that zero calibration must be refreshed from time to time. Calibration of zero

must follow a gain calibration. The zero (spectral) needs to be experimentally recorded (no manual

edition is possible).

To calibrate the zero:

− Double click on the trend area to display calibration window.

− Stop the belt if the belt was moving. Remove any sample and standard from the belt.

− Click on the button to start the zero (spectral) determination. The time countdown is displayed

in the right top corner.

Automatic calibration for U, Th and K channels:

The calibration for U, Th and K can be operated in either automatic or manual mode. Channels

calibration must be refreshed from time to time to fit the probe response drift with aging. In order

to calibrate U, Th and K in sequence:

− Double click on the trend area to pop up calibration window.

− Check and adjust the Reference values as per the certificates.

− Stop the belt if the belt was moving. Remove any sample and standard from the belt.

− Install the standard U over the detector in the lead tunnel, and then click on the button

accordingly to start a spectrum scan.

− The running process title and the time countdown are displayed in the top right corner of the

trend window.

− After completion of the spectrum acquisition, the countdown is reset and the probe amplifier is

automatically adjusted to match the region of interest of the standard.

− Repeat theses steps in sequence similarly for Th and then K standards.

Experiment operation After completing the calibrations (belt, gain, zero and U, Th and K channels), you can start the

measurement of your core samples. Lay the cores in order of depth with the shallow end nearest to the

lead tunnel. Align the first core with the groove each side of the belt. Avoid installing the cores far from

the longitudinal axis (Fig 8). The operation can be done manually or automatically.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 19

Figure 8: Illustration of core laying on the conveyor

Manual operation:

Manual operation is possible for specific uses disconnected from spectral logging. In case

you run the spectrum acquisition manually, the duration is free and the conveyor can be

stopped. This function can be used for checking the level of cores before selecting the

conveyor speed for instance.

The conveyor manual operation is basically used during of speed calibration. If you run the

conveyor at the same time as manual spectral acquisition, you cannot link the position with

the depth. Therefore, a spectral gamma logging should be conducted in automatic mode.

Figure 9: Illustration of input value dialogue box

-To run the conveyor from the interface application, you can access to the belt speed set point

(bottom left) and to the ON / OFF switch (bottom right). Click in the window to pop up input

value dialogue box (Fig. 9).

-Type a value in the range from 0.15 to 0.75 ft/min and validate with OK.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 20

-Click on button labeled “Click to start the belt” to start the conveyor. When facing the electrical

cabinet, the belt moves from left to right. To stop the conveyor, click on button labeled “Click to

stop the belt”.

-You can start the spectral acquisition by clicking on GO. The spectral radioactivity (counts in Y axis,

energy in X axis) is refreshed continuously. Equivalent values of Uranium, Thorium and K

(potassium) and total activity are directly displayed at the bottom of the window, according to

calibration data. The Y axis is auto ranged and the scale is displayed in the top left corner.

-Click in the spectrum trend window (Fig 10): a vertical line is drawn at the mouse position. The

energy level (X value) is displayed and the total counts (Y value) is refreshed continuously.

-You can stop the spectral acquisition by clicking on the button Stop. The spectral trend remains

displayed as the relevant concentration of U, Th, K and the total activity.

Note: When you click on clear, the curve, the relevant concentration of U, Th, K and the total

activity are cleared out from the memory.

Figure 10: Illustration of the spectrum trend window

Automatic operation:

-To start the spectral acquisition, click on the button “Start Measure”. After a few seconds, you are

requested to name the file that will be used for your report. Here we select "MyReport". If this

name does not exist yet, this file will be created as a copy of the master GammaLogger.xls. The

file is opened. If a file with this name has already existed, it will be open. You are prompted to

check the parameters and to press start. It is time to edit the core identification and check the

belt speed as follow (Fig 11).

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 21

Figure 11: Illustration of the spectral gamma ray report file

-You can edit the yellow cells only (column B). For instance, you cannot edit the belt speed directly.

The belt speed is calculated from the Sample Increment and the Sample Duration that you can

edit. In this example the current depth is 1,004 ft, and the initial depth is 1,000. This illustrates

how to go on with a file used earlier. In this case, the previous data from 1,000 to 1,003 will be

kept and the core scan starts from 1,004. Therefore, the Active Line (calculated by Excel) is 17;

in front of the Sample Depth 1,004. Note: In case you set the current depth to 1,002 ft, and the

core scan starts from 1,004. The data from 1,000 to 1,002 (excluded) will be kept, and the data

from 1,002 (inclusive) will be overwritten with new data. Moreover, changing the sample

increment or duration, will change the belt speed and the sample depth (automatic

recalculation).

-In our example the Sample Increment is 1 foot. We can skip 1, 2, 3 feet or any multiple of the

Sample Increment. To skip a missing core section, just enter "1" in the suitable cell(s) in the

column B in regard of the relative depth. In our XLS illustration, we skip the samples l,006

and 1,007. Finally we scan the sample beginning at depth 1,005, then we go on with the

sample beginning at 1,008 depth.

Page 22: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 22

-Once the previous steps are completed, click on start to run the experiment.

-Confirm the sample depth read at current depth in the XLS file. If you want to change, click on NO.

-On the experiment is completed, the XLS file is automatically saved and closed. Open the

MyReportxls (in our example, the report file was named by the operator "MyReport"). The path

is: C:\AppliLab\Project\NGL200\Excel Files\MyReport.xls.

-Open the tab GammaLog. We can see the values of equivalent U, Th, K and total gAPI interpreted

from the calibration versus the sample depth (Fig 12).

Figure 12 : Illustration of the values of equivalent U, Th, K and total gAPI interpreted from the

calibration versus the sample depth in the report

-Open the tab Graph. We can see the values of equivalent U, Th, K and total gAPI interpreted from the

calibration versus the sample depth (Fig 13).

Page 23: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 23

Figure 13: Illustration of the variation of equivalent U, Th, K and total gAPI interpreted from the

calibration versus the sample depth

Maintenance • Check that nothing can obstruct the belt motion.

• Check that drums and rollers are aligned to drive the belt in straight line.

• A lateral drift of 2 - 3 cm is not a problem if the belt comes back to the initial position.

• Avoid to load the cores far from the longitudinal axis

• Check the belt and chain tension once a month.

• Check that the motor fan is still efficient to cool the motor once a year.

Page 24: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 24

2-Cleaning and saturation determination After preparing the core plugs samples, the core samples must be cleaned of residual fluids and

thoroughly dried. The cleaning process may also be apart of fluid saturation determination. Let us

first define the fluid saturation as the ratio of the fluid volume in a given core sample to the

pore volume of the sample. Mathematically this is:

1

gw ow o g

p p p

w o g

VV VS S SV V V

S S S

= = =

+ + =

where wV , oV , gV and pV are water, oil, gas and pore volumes respectively and , ,w o gS S S are water, oil

and gas saturations. Note that fluid saturation may be reported either as a fraction of total porosity or as

a fraction of the effective porosity. Since fluid in pore spaces that are not interconnected can not be

produced from a well, the saturations are more meaningful if expressed on the basis of the effective

porosity. The weight of water collected from the sample is calculated from the volume of water by:

w w wW Vρ=

Where wρ is water density in g/cm3. The weight of oil removed from the core may be computed as,

o l wW W W= −

Where lW is the weight of liquids leaving the core sample in gr. Oil volume may then be calculated as

/o oW ρ . Pore volume pV is determined by a porosity measurement, and oil and water saturation may be

calculated by the above equation. Gas saturation can be determined using the summation equation.

There are several methods to clean and evaluate the fluid saturation within a core plug sample. Here we

briefly review some of them:

1-Direct Injection of Solvent

The solvent is injected into the sample in a continuous process. The sample is held in a rubber sleeve

thus forcing the flow to be uniaxial.

2-Centrifuge Flushing A centrifuge which has been fitted with a special head sprays warm solvent onto the sample. The

centrifugal force then moves the solvent through the sample. The used solvent can be collected and

recycled

Page 25: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 25

3-Gas Driven Solvent Extraction The sample is placed in a pressurized vessel of solvent containing dissolved gas. The solvent fills the

pores of sample. When the pressure is decreased, the gas comes out of solution; expands, and drives

fluids out of the rock pore space. This process can be repeated as many times as necessary

4-Soxhlet Extraction A Soxhlet extraction apparatus is the most common method for cleaning sample, and is routinely used

by most laboratories. As shown in Fig. 14a, toluene is brought into a slow boil in a Pyrex flask, its

vapors move upwards and the core becomes engulfed in the toluene vapors (at approximately 110 C).

Eventually the amount of water within the core sample in the thimble will be vaporized. The toluene

and water vapors enter the inner chamber of the condenser; the cold water circulating around the inner

chamber condenses both vapors to immiscible liquids. Recondensed toluene together with liquid water

falls from the base of the condenser onto the core sample in the thimble; the toluene soaks the core

sample and dissolves any oil with which it conic into contact. When the liquid level within the Soxhlet

tube reaches the top of the siphon tube arrangement, the liquids within the Soxhlet tube are

automatically emptied by a siphon effect and flow into the boiling flask. The toluene is then ready to

start another cycle. A complete extraction may take several days to several weeks in the case of low

API gravity crude or presence of heavy residual hydrocarbon deposit within the core. Low permeability

rock may also require a long extraction time

Figure 14: Schematic diagram of (a) Soxhlet and (b) Dean- Stark apparatus

Page 26: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 26

5-Dean-Stark Distillation-Extraction The Dean-Stark distillation provides a direct determination of water content. The oil and water area

extracted by dripping a solvent, usually toluene or a mixture of acetone and chloroform, over the plug

samples. In this method, the water and solvent are vaporized, recondensed in a cooled tube in the top of

the apparatus and the water is collected in a calibrated chamber (Fig. 14b). The solvent overflows and

drips back over the samples. The oil removed from the samples remains in solution in the solvent. Oil

content is calculated by the difference between the weight of water recovered and the total weight loss

after extraction and drying.

6-Vacuum Distillation The oil and water content of cores may be determined by this method. As shown in Fig. 15, a sample is

placed within a leak-proof vacuum system and heated to a maximum temperature of 230oC. Liquids

within the sample are vaporized and passed through a condensing column that is cooled by liquid

nitrogen.

Figure 15: Vacuum distillation Apparatus

7-Retort Oven The retort oven is used to determine the porosity and total saturation of water (Sw) and residual

saturation of oil (Sro) in core samples, either fresh or preserved ones.

Page 27: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 27

Comparison of these methods: The direct-injection method is effective, but it is slow. The method of flushing by using centrifuge is

limited to plug-sized samples. The samples also must have sufficient mechanical strength to withstand

the stress imposed by centrifuging. However, the procedure is fast. The gas driven-extraction method is

slow. The disadvantage here is that it is not suitable for poorly consolidated samples or chalky

limestones. The distillation in a Soxhlet apparatus is slow, but is gentle on the samples. The procedure

is simple and very accurate water content determination can be made. Vacuum distillation is often used

for full diameter cores because the process is relatively rapid. Vacuum distillation is also frequently

used for poorly consolidated cores since the process does not damage the sample. The oil and water

values are measured directly and dependently of each other.

In each of these methods, the number of cycles or amount of solvent which must be used depends on

the nature of the hydrocarbons being; removed and the solvent used. Often, more than one solvent must

be used to clean a sample. The solvents selected must not react with the minerals in the core. The

commonly used solvents are: acetone/benzene, benzes/methol alcohol, carbon/tetrachloride,

chloroform, methylene dichloride, mexane, naphtha, tetra chloroethylene, toluene, trichloro ethylene

and xylene. Toluene and benzene are most frequently used to remove oil and methanol and water is

used to remove salt from interstitial or filtrate water. The cleaning procedures used are specifically

important in special core analysis tests, as the cleaning itself may change wettabilities. The core sample

is dried for the purpose of removing connate water from the pores, or to remove solvents used in

cleaning the cores. When hydratable minerals are present, the drying procedure is critical since

interstitial water must be removed without mineral alteration. Drying is commonly performed in a

regular oven or a vacuum oven at temperatures between 50°C to 105oC. If problems with clay are

expected, drying the samples at 60°C and 40 % relative humidity will not damage the samples.

2-1 Dean Stark The distillation extraction (Dean stark) method for determination of the fluid saturation depends upon

the distillation of the water fraction, and the solvent extraction of the oil fraction from the sample. The

sample is weighed and the water fraction is vaporized by boiling solvent. The water is condensed and

collected in a calibrated receiver. Vaporized solvent also condenses, soaks the sample, and extracts the

oil. The sample is oven dried and weighed. The oil content is determined by gravimetric difference.

Page 28: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 28

Machine Description This consists of a distillation / extraction glassware unit and a heating mantle with thermostatic

controller. The glassware for one sample is composed of boiling flask with extractor, a sample support

screen, volumetrically graduated water receiving tube of 5 or 10 ml, condenser and desiccant drying

tube. A soft tubing is also used to connect the condenser to the water cooling unit. All these devices are

mounted on a frame rack (Fig.16).

Figure 16: Dean Stark apparatus model (left) DS_1.5”x6 and (right) DS_4”x3

Experiment operation: The objective of the experiment is to determine the oil, water and gas saturation of a core sample. The

procedure is as foolow:

1. Weigh a clean, dry cellulose thimble. Use tongs to handle the thimble.

2. Place the cylindrical core plug inside the thimble, then quickly weigh the thimble and sample.

3. Fill the extraction flask two-thirds full with toluene. Place the thimble with sample into the long

neck flask.

4. Tighten the ground joint fittings. Start circulating cold water in the condenser.

5. Turn on the heater and adjust the rate of boiling so that the reflux from the condenser is a few

drops of solvent per second. The water circulation rate should be adjusted so that excessive

cooling does not prevent the condenser solvent from reaching the core sample.

Page 29: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 29

6. Continue the extraction until the solvent is clear.

7. Read the volume of collected water in the graduated tube. Turn off the heater and cooling water

and place the sample into the oven (from 105°C to 120°C), until the sample weight does not

change. The dried sample should be stored in a desiccater.

8. Obtain the weight of the thimble and the dry core.

9. Calculate the loss in weight Wl , of the core sample due to the removal of oil and water.

10. Measure the density of a separate sample of the oil.

11. Calculate the oil, water and gas saturations after the pore volume Vp of the sample is

determined.

Table 2: Data sheet for Dean Stark experiment

Worg

gr

Wdry

gr wρ

gr/cc

gr/cc

Vw

cc

Wo

gr

Vo

cc

Vp

cc So Sw Sg

Worg = Weight of original saturated sample

Wdry = Weight of desaturated and dry sample

2-2 Retort Oven The retort oven is used to determine the porosity and total saturation of water (Sw) as well as the

residual saturation of oil (Sro) in the fresh or preserved core samples (Fig. 17). Note that the saturations

which are determined in a laboratory are generally different from the field saturations. These

differences come from:

• Invasion of drilling mud, or of mud filtrate

• Expansion of gas due to pressure drop during upraise of core to surface

• To some errors of manipulations, as core sample washing with water or drying without cares

Page 30: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 30

Figure 17: A retort oven device

Machine Description The retort oven is composed of following items:

• Insulated oven with heat control with a maximum operating temperature of 700 °C.

• 12 traps and stainless steel screens

• stainless steel tank for condensed water

The procedure of the test is as follow:

• Install water supply to each end of bath which has a baffle in centre, ie each end independent of

other end.

• Set required temperature using UP and DOWN arrows buttons only.

• Heat the chamber (cover closed) to 540-650 °C (1000–1200 °F). When retort cups are placed in

the heated enclosure, the temperature will fall down about 400 °C, and then will go up again.

• The fresh sample is roughly crushed, weight = 125 grams, and placed in the retort cup.

• Volume of the crushed sample = VT with VT = Weight / Natural density

Note : measurement must be realized on an another piece of core whatever is its form, about 30

cm3, weighed with its fluids, water, oil, gas and with total volume will have been determined

with a volumetric pump.

• Place all the retort cups (12 max) in the retort, even there is no sample to analyze in each of

them and close the retort which is under voltage. The receiving graduated 20 cc tubes clean are

in place.

Page 31: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 31

• Read the volume of water “INI.W” collected after “T” minutes. This time “T” corresponds

exclusively to the water contained into the pores of the sample and not to the water contained

into the clays. It is determined in pointing out according to the time (or to the temperature) the

volume of water collected into the receiving tubes. It is the value of the time which corresponds

with the middle of the plateau, or of the inflection point (in case of clayey samples).

• Read the volume of water “FINAL W” collected when temperature reaches 650 °C.

• Read the volume of oil “OBS.O” collected when the temperature reaches 650 °C. This quantity

of oil collected is by default because oil is lost by cracking during heating, from which a

calibration is needed.

Calibration In sands samples contained in retort cups, one places growing known quantities of oil from Occ to

10cc. Using normally the retort oven, one notes the “OBS.O” volumes. Then plot working curves of

correction: see correction table (for example a retort oven and crude oil 45° API)

Table 3: calibration table

Reading observed,

“OBS.O” cc

Reading corrected,

“CORR.O” cc

0

traces

0.05

0.1

0.2

1.0

0

0.1

0.15

0.25

0.35

1.40

For reading higher then 1.0 cc, add 0.4 to determine the corrected volume. Correction of the volume of

oil collected. Use the precedent table. It is determined “CORR.O”.

Calculation Amount of oil in the sample:

. 100CORR OObVT

= ×

Page 32: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 32

Amount of water in the sample:

. 100INIT WWbVT

= ×

Amount of gas contained in the sample Gb is determined by volumetric mercury pump.

Porosity : Ob Wb Gbφ = + +

Total saturation of water : 100TWWbSφ

=

Residual saturation of oil :

100ROObSφ

=

2-3 Core Saturator Prior to perform any core flood experiment, we need a saturated rock sample. Automatic saturator is

a device used to prepare samples for such experiments. The automatic saturator is used to inject water

or brine into the sample.

Machine Description This machine can either work on automatic mode and semi-automatic mode. Although standard

parameters fulfil most of applications, the operator can easily change the duration steps of the

automated mode. Furthermore, it is possible to shift to semi-auto or manual mode for any specific

process. In the semi automated mode the operator controls the Electro-Valves, as in the manual mode

where the operator work with the manual valves. In semi-auto and manual mode the steps duration and

valve sequence is custom. For very low permeability samples, you can increase the "additional sample

evacuation" step to evacuate the samples longer than the saturant (and avoid vaporization and salt

concentration change or precipitation). This system is composed of the following items as shown in

Fig. 18 and its main feature is summarized in Table 4.

• A console with injection pump, valves and PLC (Programmable Logical Controller)

• 2 jars (one saturant TANK, one vacuum TRAP)

• A pressure vessel

• A vacuum pump

Page 33: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 33

Figure 18: Main components of the automatic saturator

Table 4: Main features of automatic saturator

psi 2000 Maximum saturating pressure

mm 58 Cell diameter

mm300 Cell height

VAC, 50 Hz 220 Power supply

To achieve a good quality saturation on a low permeability sample, thoroughly evacuation (sample and

test brine) is followed by saturation at pressure controlled via a turn-key unattended program.

Experiment operation: To do the experiment, some pre-steps to prepare the system are necessary before using either

automatic, semi-auto or manual modes. These are four main steps to prepare the system:

i)Setting the target pressure. For setting the target pressure you can use the knob on the pressure gauge.

You can change the set point by rotating the knob to move the red tip needle to the requested value.

(Fig. 19)

Page 34: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 34

Figure 19: Setting the target pressure

ii)Setting the pump. The pump panel is located at the right low corner of the console (Fig. 20left).

Screw the knob to reduce the flow rate. The setting must be at least higher than 30% of the range (Fig.

20right). Before starting an automatic process, switch “On” the pump. If you plan to run a semi-

automatic mode or manual mode, you will switch on the pump on request.

Figure 20: Illustration of: (left) setting the pump and (right) pump flow rate

iii)Sample loading. Discharge the pressure in the unit by setting the manual valves MV3 to by-pass and

MV2 to vent. Disconnect the tubing from the lid. Then open the cell by unscrewing the lid. After you

are checking the sample identification, install the sample with the tray into saturator cell. Eeventually

complete the volume with some plain plugs in order to reduce the volume of brine to inject (Fig. 21).

Figure 21: Illustration of sample loading

Page 35: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 35

Check the lid seal. Screw the lid to the pressure vessel. Connect back the tubing. Install the tray with

samples into the saturator cell. Check the lid seal. Figure 22 shows a home-made hook to lift the tray.

Figure 22: Illustration of hooking to lift the tray

iv)Jars preparation. Poor the saturant (brine) into the tank jar (2 ports model). Let enough free space for

bubbling during degassing. Empty the water trapped in the jar (1 port) connected to the vacuum pump.

Close the two jars. (Fig. 23)

Figure 23: Illustration of jar preparation step

1-Automatic mode

• Switch the selector in horizontal position to Automatic option. The green bulb is lightening.

• Press on the button START, the green bulb "IN PROGRESS" is lightening.

Page 36: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 36

• There are six steps (sample and saturant evacuation, sample additional saturation, saturant to atm

pressure, by-pass opens, pump priming, saturation under pressure) that are processed automatically.

• Once the cycle is completed, the green bulb "COMPLETE" is lightening.

• You can abort the cycle at any time by pressing on the STOP button. Check the pressure and the

pumps status.

Figure 24 shows the switch time table with default time span. The global duration is about 3 1/2 hour.

The long durations are respectively T6 (saturation under pressure), T2 (additional saturation), T1

(sample and saturant evacuation) and for 2, 1½ and 1 hours. Others durations are similar to a

commutation time. Note that any of these durations can be modified. The sample and saturant

evacuation step start simultaneously with T2 but as soon as T2 is elapsed, the saturant is isolated while

the sample goes on to be evacuated until T1 is elapsed. This allows evacuating the saturant for a shorter

time T2 than the sample evacuated during T1 and to prevent from potential saturant evaporation (in

case of brine etc). Make sure that no manual valve is set open during semi-auto process.

Stop

End

of S

tep

# 1

End

of S

tep

# 2

End

of S

tep

# 3

End

of S

tep

# 4

End

of S

tep

# 5

End

of S

tep

# 6

Start

Sam

ple

and

Satu

rant

evac

uatio

n

CompletedIn progress

Sam

ple

addi

tiona

lev

acua

tion

Satu

rant

to a

tm. p

ress

.

By-

pass

ope

n

Pum

p Pr

imin

g

Satu

ratio

n @

pre

ssur

e

ONEV4 EV4ONEV5 EV5

ONEV6 EV6ONEV7 EV7

ONEV8 EV8Pump run Pump

T5 : 1'T4 : 2'T3 : 1' T6 : 120 '

afterabout3 1/2 h

T2 : 60 '

T1 : 90 '

Figure 24: The time duration of six steps used in the automatic mode

Step1: Samples and brine evacuation with T2 = 60 min (note that T1 starts simultaneously)

• The valves EV4 and EV5 are open to the vacuum pump during T2 (not T1)

Page 37: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 37

• Check that the vacuum pump is running and bubbles appear immediately in the saturant jar (as for

boiling water). If no bubble comes after the first minute elapsed, stop the process and fix the leak.

• Check that no saturant (brine) is going out from the trap jar to the vacuum pump.

Step 2: Relieving vacuum in the brine jar with T1 = 90 min, ends 30 min after T2

• The valve EV5 is closed to isolate saturant brine jar from the vacuum pump. T2 (1 minute default

value) is devoted to these operations (see Fig. 25 for the steps 1 & 2)

Vacuum

Vent

85

6

7

4

By-Pass

Pump(stopped)

Vacuum

Vent

85(open)

6

7(closed)

4

By-Pass

Step#1 Sample & Saturant evacuation T2=60 min Step#2 Sample additional evacuation T1-T2=30 minT1=90min starts at same time as T2

Figure 25: Illustration of the schematic connections used in the steps 1 and 2

Step 3: Saturant to atmosphere pressure with T3 = 1 min

• The valve EV8 is open: the vacuum is relieved in the desaturant jar. The brine pressure builds up to

atmospheric but stay degassed.

• You can stop the vacuum pump.

step 4: By-pass opens with T4 = 2 min

• The by-pass EV6 is open, thus the saturant invades the sample vessel under push-pull action of

atmospheric pressure at valve EV8 and vacuum at valve EV4 (see Fig. 26 for the steps 3 & 4)

Page 38: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 38

Vacuum

Vent

85

6

7

4

By-Pass

Vacuum

Vent

85

6

7

4

By-Pass

Step# 3 Saturant to atm. pressure T3 = 1 min Step#4 By-pass open T4 = 2 min Figure 26: Illustration of the schematic connections used in the steps 3 and 4

Step5: Pump priming with T5 = 1 min

• Ev7 is open to feed the pump with the saturant

• The pump starts and is primed.

Vacuum

Vent

85

6

7

4

By-Pass

Pump run

Vacuum

Vent

85

6

7

4

By-Pass

Step#6 Saturation @ pressure T6 = 120 minStep#5 Pump priming T5 = 1 min Figure 27: Illustration of the schematic connections used in the steps 5 and 6

Page 39: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 39

Step6: Pressuring the sample vessel with T6 = 120 min.

• Ev6 is closed. The saturant path is through the pump only.

• The injection pump hold on (stops temporarily) as the pressure set point ("target") is reached.

If the pressure decreases before T6 is elapsed, the pump restarts to build-up the pressure up back to the

target value. This ensures the saturation of low permeability samples (see Fig. 27 for the steps 5 & 6)

2-semi automatic mode

Semi auto mode is a custom process where operator uses the appropriate switches, as in manual mode.

For this switch the selector to Manual. To operate the electro-valves: press once the button of a valve,

the green bulb switches lightening as the valves open. Press once again to close the valve. (Fig. 28)

Figure 28: button of valves panel from which the operating mode can be changed

Note that you run a single mode at once (e.g. semi-auto, automatic or manual). Also when an automatic

mode is running, just press the STOP button before starting a manual mode.

3-Manual mode

Manual mode is a custom process where operator adjusts the EV valves manually. Make sure that no

electro-valve is set open during manual process. Switch the selector to Manual. You can open as many

valves as you want at the same time and run any step of yours as long as required. Figure 29 shows the

various status of tank.

The valves and pump sequence to reproduce the automatic process in the manual mode is as follow:

• Check that the vacuum pump is running and bubbles appear immediately in the saturant jar (as if

the water was boiling). If no bubble comes within the first minute, stop the process and fix the leak.

• Check that no desaturant (brine) is going out from the trap jar to the vacuum pump.

Page 40: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 40

Figure 29: Illustration of tank status by setting it to: the vent, the vacuum pump, be isolated

There are 7 steps with various the ellipse(s), point(s) and the valve(s) actions. You can set custom

duration for each step. The default duration is summarized in Table 5:

Table 5: A summery of the default durations for 7 steps

Step Duration

(min)

Process

1 30 Global evacuation,

2 60 Sample additional evacuation

3 1 Relieving vacuum in saturant tank

4 2 By-pass open

5 1 Pump priming

6 120 Sample saturation at pressure

7 ∝ Release vessel pressure

These are the description of various steps. Also Fig. 30 show the connections at each step.

step 1: set V2 to the vacuum (global evacuation).

step 2: set V2 to the close and set V1 to the vacuum (sample additional evacuation).

step 3: set V3 to the vent (relieving vacuum in saturant tank)

step 4: set V3 to the By-pass (by-pass open)

step 5: set V3 to the pump (pump priming)

step 6: stop the vacuum pump and set V1 to the close (pump brine into core vessel for 120 min)

step 7: Finally, cycle is completed.

Page 41: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 41

Manual Step 2:Sample Evacuation

Manual Step 1:Global Evacuation

Vent 2 1

3

Vent2 1

3

Vacuum

Closed

Closed

Stop

Vacuum Vacuum

(Action )

Vent 2 1

3

Manual Step 3: Relievingvacuum in the brine tank

Vent 2 1

3

Manual Step 4:By-pass open

Vent

Vacuum Vacuum

By-pass

Pump

Manual Step 5:Pump priming

Vacuum

Vent2 1

3Run

Vent2 1

3

Manual Step 6:Sample saturation @pressure

Vacuum

Vent2 1

3

Manual Step 7:Release the vessel pressure

By-passStop

Vacuum

Figure 30: Illustration of the schematic connections used in the steps 1-7

Page 42: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 42

3-Porosity From the viewpoint of petroleum engineers one of the most important property of a reservoir rock is

porosity. Porosity is a measure of storage capacity of a reservoir. It is defined as the ratio of the pore

volume to bulk volume, and it may be expressed as either a percent or a fraction,

PoreVolume BulkVolume Grain VolumeBulkVolume BulkVolume

φ−

= =

Two types of porosity are total or absolute porosity and effective porosity. Total porosity is the ratio

of all the pore spaces in a rock to the bulk volume of the rock while the effective porosity eφ is the ratio

of interconnected void spaces to the bulk volume. Thus, only the effective porosity contains fluids that

can be produced from wells. For granular materials such as sandstone, the effective porosity may

approach the total porosity, however, for shales and for highly cemented or vugular rocks such as some

limestones, large variations may exist between effective and total porosity.

Porosity may be classified according to its origin as either primary or secondary. Primary or original

porosity developed during deposition of the sediment. Secondary porosity is caused by some geologic

process subsequent to formation of the deposit. These changes in the original pore spaces may be

created by ground stresses, water movement, or various types of geological activities after the original

sediments were deposited. Fracturing or formation of solution cavities often will increase the original

porosity of the rock.

Figure 31: Cubic packing (a), rhombohedral (b), cubic packing with two grain sizes (c), and

typical sand with irregular grain shape (d).

Grain size distribution and sorting can influence the porosity. For a uniform rock grain size,

porosity is independent of the size of the grains. A maximum theoretical porosity of 48% is achieved

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 43

with cubic packing of spherical grains, as shown in Fig. 31a. Rhombohedral packing, which is more

representative of reservoir conditions, is shown in Fig. 31b; the porosity for this packing is 26%. If a

second, smaller size of spherical grains is introduced into cubic packing Fig. 33c, the porosity

decreases from 48 to 14%. Thus, porosity is dependent on the grain size distribution and the

arrangement of the grains, as well as the amount of cementing materials. Not all grains are spherical,

and grain shape also influences porosity. Typical reservoir sand is illustrated in Fig. 31d.

Moreover, the rock compaction can affect the porosity. This is the process of volume reduction due

to an externally applied pressure. For extreme compaction pressures, all materials show some

irreversible change in porosity. This is due to distortion and crushing of the grain or matrix elements of

the materials, and in some cases, recrystallization. The variation of porosity with change in pressure

can be represented by, 2 1( )

2 1fC P Peφ φ −=

Where 2φ and 1φ are porosities at pressure 2P and 1P respectively, and Cf is formation

compressibility. Formation compressibility is defined as summation of both grain and pore

compressibility. For most petroleum reservoirs, grain compressibility is considered to be

negligible. Formation compressibility can be expressed as, 1f

dVCV dP

= where dP is change

in reservoir pressure. For porous rocks, the compressibility depends explicitly on porosity.

Porosity measurement on core plugs: The porosity of reservoir rock may be determined by using core analysis, well logging technique or

well testing. The question of which source of porosity data is more reliable can not be answered

without reference to a specific interpretation problem. These techniques can all give correct porosity

values under favorable conditions. The porosity determined from core analysis has the advantage that

no assumption needs to be made as to mineral composition, borehole effects, etc. However, since the

volume of the core is less than the rock volume which is investigated by a logging device, porosity

values derived from logs are frequently more accurate in the case of heterogeneous reservoirs.

From the definition of porosity, it is evident that the porosity of a sample of porous material can be

determined by measuring any two of the three quantities: bulk volume, pore volume or grain volume

from core plugs (Fig. 32).

Page 44: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 44

Figure 32: representation of the different volumes in a plug

i) Bulk volume: Although the bulk volume may be computed from measurements of the dimensions of a uniformly

shaped sample, the usual procedure utilizes the observation of the volume of fluid displaced by the

sample. The fluid displaced by a sample can be observed either volumetrically or gravimetrically. In

either procedure it is necessary to prevent the fluid penetration into the pore space of the rock. This

can be accomplished by:

(1) coating the sample with paraffin or a similar substance,

(2) saturating the core with the fluid into which it is to be immersed, or

(3) using mercury.

Gravimetric determinations of bulk volume can be accomplished by observing the loss in the weight

of the sample when immersed in a fluid or by change in weight of a pycnometer with and without

the core sample.

ii) Pore volume: All the methods measuring pore volume yield effective porosity. The methods are based on either the

extraction of a fluid from the rock or the introduction of a fluid into the pore spaces of the rock. One

of the commonly used methods is the helium technique, which employs Boyle's law. The helium gas

in the reference cell isothermally expands into a sample cell. After expansion, the resultant

equilibrium pressure is measured. The Helium porosimeter apparatus is shown schematically in

Error! Reference source not found.

Helium has the following advantages over other gases:

(I) Its small molecules rapidly penetrate into small pores.

(2) It is an inert gas and does not adsorb on rock surfaces (air may do),

(3) It can be an ideal gas (i.e., z = 1.0) for pressures and temperatures usually used in the test,

Page 45: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 45

(4) It has a high diffusivity so affords a useful mean for determining porosity of low

permeability rocks.

Figure 33: Schematic diagram of helium porosimeter apparatus.

The schematic diagram of the helium porosimeter shown in Fig. 33 has a reference volume V1, at

pressure P and a matrix cup with unknown volume V2, and initial pressure P2. The reference cell and

the matrix cup are connected by tubing; the system can be brought to equilibrium when the core holder

valve is opened, allowing determination of the unknown volume by measuring the resultant equilibrium

pressure p. (pressure P1 and P2 are controlled by the operator; usually P1 = 100 and P2=0 psig). When

the core holder valve is opened, the volume of the system will be the equilibrium volume V, which is

the sum of the volumes V1 and V2. Boyle's law is applicable if the expansion takes place isothermally.

Thus the pressure-volume products are equal before and after opening the core holder valve:

( )1 1 2 2 1 2PV PV P V V+ = +

Solving the equation for the unknown volume, V2 gives,

1 12

2

( )P P VVP P−

=−

Since all pressures in above equation must be absolute and it is customary to set P1= 100 psig and P2=0,

the equation may be simplified as follows:

12

(100 )V PVP

−=

where V2 in cm3 is the unknown volume in the matrix cup, and V1 is the known volume of the

reference cell. p (psi) is pressure read directly from the gauge. Small volume changes occur in the

Page 46: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 46

system, including the changes in tubing and fittings caused by pressure changes during equalization. A

correction factor may be introduced to correct for the composite system expansion. The correction

factor is determined for porosimeters before they leave the manufacturer, and this correction is built

into the gauge calibration in such a way that it is possible to read the volumes directly from the gauge.

Another method of pore volume determination is to saturate the sample with a liquid of known density,

and noting the weight increase (gravimetric method).

When a rock has a small fraction of void space, it is difficult to measure porosity by the mentioned

methods. In this case, mercury injection (Fig. 34a) is used which has the principle of forcing mercury

under relatively high pressure in the rock pores. A pressure gauge is attached to the cylinder for reading

pressure under which measuring fluid is forced into the pores. Fig. 34b shows a typical curve obtained

from the mercury injection method. The volume of mercury entering the core sample is obtained from

the device with accuracy up to 0.01 cm3.

Figure 34: Mercury injection pump (a) and porosity through mercury injection (b).

iii) Grain volume: The grain volume of pore samples is some times calculated from sample weight and knowledge of

average density. Formations of varying lithology and, hence, grain density limit applicability of this

method. Boyle's law is often employed with helium as the gas to determine grain volume. The

technique is rapid and is valid on clean and dry sample. The measurement of the grain volume of a core

sample may also be based on the loss in weight of a saturated sample plunged in a liquid.

Grain volume may be measured by crushing a dry and clean core sample. The volume of crushed

sample is then determined by (either pycnometer or) immersing in a suitable liquid.

Page 47: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 47

3-1 Hg porometer The Mercury Pump is designed to measure the bulk volume of a sample and also pore volume in a dry

core sample. By measuring these two parameters, porosity of the sample can be calculated. The

Mercury Pump has the advantage to allow very rapid measurements of regularly or irregularly shaped

core samples. However, students should consider the following saftey notices:

• Any doubt must be resolved before performing a test or maintenance.

• Protect yourself from any mercury contact by wearing overall.

• The pycnometer lid has a rapid lock closure with O'ring seal. This O'ring ensures the tightness

of the system. Make sure it is not damaged and installed in the groove correctly.

• Do not let other liquids in the system.

• Make sure the sample is removed after each experiment

Machine Description: The Hg porometer is based on a volumetric pump attached to a sample vessel. The vessel is used as a

pycnometer. The pycnometer lid has a rapid lock closure with O'ring seal. A needle valve (also named

drain plug) in the lid opens the chamber to atmosphere. The movement of the pump metering plunger

is indicated on a volume gauge. The pressure in the pycnometer is read on the vacuum gauge or on the

pressure gauge (according to the sequence).

The main machine parts are shown in Fig. 35.

Figure 35: Hg porometer

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 48

The hand wheel dial is graduated in 0.01 of rotation subdivisions and permits estimation of plunger

displacement to 0.005 rotation. Due to mechanical transmission, each rotation is equivalent to 1.375 cc.

Fig. 36 shows an example of reading rounded to 0.01 rotation. The red figure of the counter is reported

on the clock dial. When you can read 56.1 on the counter ("56" in black color, "1" in red color) and the

clock dial displays 1.3, the global reading is 56.13 rotations.

Figure 36: Volume gauge

The reading on the volume gauge multiplied by 1.375 gives the actual volume. Some features of the

system are mentioned in Table 6.

Table 6: Some features of Hg porometer apparatus

Maximum pressure 1,500 psi (approx. 100

bar)

Pump volume 100 cc

Core sample maximum size Diameter 1"½

Length 3"

Wetted part Stainless steel

Experiment operation The following steps must be performed:

1. Make sure the pycnometer is empty (no sample inside).

2. Lock the lid and open the drain plug by one turn.

3. Inject the mercury (turn the wheel anticlockwise) until the first bead of mercury appears at the drain

outlet.

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 49

4. Write down the dial read at the volume gauge.

5. Withdraw the plunger a short to empty the pycnometer.

6. Make sure to allow enough void space to prevent from overflow when closing the lid with the

sample in place.

7. Open the drain plug by one turn.

8. Open the pycnometer.

9. Install the sample into the pycnometer. Make sure that the sample dimensions are compatible with

the specification.

10. Close and lock the lid, leaving the drain plug open.

11. Inject the mercury until the first bead of mercury appears at the drain outlet.

12. Write down the dial read at the volume gauge. The pycnometer is full: the void space is

occupied by mercury and the sample. The pressure is atmospheric; the pore volume is not invaded.

13. Close the drain plug.

14. Turn the hand wheel in order to build up the pressure up to the reference value (typically 750 psi).

15. Write down the final volume .

Calculations and Report: Having done the above mentioned steps, we now are able to determine the porosity of the sample.

( )

( )1 0

1 2 where c is the volume coefficientbV c V V

c V Vφ

= −

= −

The porometer internal volume expands by a volume called correction factor when building the

pressure up to the reference pressure. The correction factor must be calibrated before any measurement

campaign. It is easy to determine this by calculating the difference of the two volume reading:

1) at atmospheric pressure and,

2) at reference pressure with the empty porometer (no sample inside).

Based on a recommended reference pressure of 750 psig (approximately 50 bar), an additive 2%

correction of the pore volume reading is necessary. Finally we determine the bulk and pore volume

Page 50: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 50

of sample by considering correction factors and fill the following table.

Table 7: Data sheet for Hg porometer experiment

V0 V0P V1 V2 C

3-2 KeyPhi instrument The KEYPHI instrument is a fully automated porosimeter (and also permeameter) used to determine

properties of plug sized core samples at reservoir confining pressure. In addition to the direct

measurement of interested properties, the instrument offers some reporting and calculation facilities

(thanks to its user-friendly windows operated software) including:

1-Direct measurements: Core length and diameter/ Pore volume/ Gas permeability

2-Calculated parameters: Sample bulk volume / Grain volume/ porosity / Grain density (if sample is

weighed)/ Klinkenberg slip factor "b"/ Klinkenberg corrected permeability/ Inertial coefficient

The gas permeability determination is based on the unsteady state method (pressure falloff ) whereas the

pore volume is determined using Boyle’s law technique. Length and diameter of the core sample are

measured with digital caliper and subsequently bulk volumes are determined automatically. The

instrument is also provided with a unique automatic core sample loading mechanism which can process

up to 20 samples. A summary of operational conditions of this instrument is given in Table 8.

Table 8: Operational conditions of KeyPhi

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 51

Moreover, the initial and final conditions are shown in Fig. 37.

At the initial condition, total numbers of gaseous moles are:

n(total) =n (helium) + n(air)

( ) ( )1

1

a d p

He a

P V VP Vr Vvntotal

Z RT Z RT

++= +

At the final condition, total numbers of gaseous moles are:

n(total )= n(helium& air)

( )2 2

2 2

r v d p r v d pHe air

total He total a

P V V V V P V V V Vn nntotal

n Z RT n Z RT

+ + + + + + = +

Figure 37: Initial and final conditions in KeyPhi

Now assuming the assumptions: P1>> Pa , and: n He >> n air thus it comes as

1 and 0He air

total total

n nn n

≅ ≅

Hence, the final material balance that gives after simplifications:

( )2

2

r v d ptotal

He

P V V V Vn

Z RT

+ + +=

Page 52: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 52

The pore volume can be easily deduced from this relationship

1 2

2 1

2

2 2

1

1

Her v

Hep d

a He

He

P ZV VP Z

V VP ZP Z

×− − × = −

×−

×

And the porosity is given by:

100 /pV BVφ =

and apparent volume of the sample is,

( )2 / 4BV D Lπ=

Experiment operation: 1. Connect the keyphi to the main power supply. Connect the air to the air inlet. Connect the N2 or

He cylinder to the gas inlet.

2. Connect the 3 way valve of the confining pump to refill position. Start the pump in Start/Empty

mode, piston is in the top position. Connect a reservoir containing the driving oil to the valve Start

the pump in Refill mode until the pump is full.

3. Connect the 3 way valve of the confining pump to confining position. The pump is ready to

transfer driving fluid into the coreholder.

4. Select the carousel corresponding to the core diameter. Put the core samples in the carousel up to

20 max. Mount the carousel on its position and screw the crank of the carousel and then close the

door.

5. Open the calibrated file you want to use to make your measures in the directory

C:\APPLILAB\PROJECT\KEYPH[\EXCEL FILE\

6. Select the "Info" sheet.

7. Fill the fields Sample ID, Weight, Atmospheric Pressure, Sample Position (in the Sample Holder),

Confining Pressure, Inlet pressure, Stability Set Point and Vacuum Time Set Point

8. Choose the measures you want to do on each sample (porosity or permeability or both)

Page 53: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 53

9. In case for a sample you only want to perform a permeability measure you have to fill the field

pore volume.

10. Save and close your file.

11. Start the measurement from software.

Figure 38: Keyphi instrument

Page 54: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 54

4-Resistivity Porous rocks, which are comprised of solid grains and void space, with the exception of certain clay

minerals are nonconductors. The electrical properties of a rock depend on the geometry of the voids

and the fluid with which those voids are filled. The fluids of interest in petroleum reservoirs are oil,

gas, and water. Oil and gas are nonconductors while water is a conductor when it contains dissolved

salts, such as NaCl, MgCl2, KCl that are normally found in formation water. Current is conducted in

water by movement of ions and can therefore be termed electrolytic conduction. The resistivity of a

porous material is defined by,

2 with: r = resistance (Ohm-meter), A = cross-sectional area (m ), L = length (m)rARL

=

For a complex material like rock containing water and oil, the resistivity of the rock depends on various

factors including water salinity, temperature, rock porosity, composition, pore geometry and formation

stress.

The resistivity of an electric current in porous rock is due primarily to the movement of dissolved ions

in the brine that fills the pore of the rock. The resistivity varies with temperature due to the increased

activity of the ions in solution as temperature increases. Due to the conductivity properties of reservoir

formation water, the electrical well-log technique is an important tool in the determination of water

saturation versus depth and thereby a reliable resource for in situ hydrocarbon evaluation. An empirical

relation for this was developed by Archie in 1942, the so called Archie’s equation for clean water-wet

sandstones over a reasonable range of water saturation and porosities. In practice, Archie’s equation

should be modified according to the rock properties: clay contents, wettability, pore distribution, etc.

The first equation to express the electrical properties of rocks is the formation factor F, defined as,

rock resistivity when saturated 100% with water, .mwater resistivity, .m

oo

ww

RRFRR

= Ω=

= Ω

Obviously, the factor depends on the pore structure of the rock. The second equation to express the

electrical properties of rocks is the resistivity index I, defined as,

rock resistivity when saturated partially with water, .mtt

o

RI R

R= = Ω

Wyllie has developed a relation between the formation factor and other rock properties, such as

porosity φ and tortuosity τ defined as ( )2/aL L where L is the length of the core and aL represents

the effective path length through the pores. Based on simple pore models the following relationship has

Page 55: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 55

been derived, /F τ φ= . Moreover, Archie has suggested a slightly different relation between the

formation factor and porosity by introducing the Archie’s cementation factor, m as: mF φ −= with the

cementation factor in the range [1.8-2.0] for consolidated sandstones and about 1.3 for clean

unconsolidated sands. The famous Archie’s equation gives the relationship of resistivity index with

water saturation of rocks through saturation exponent, n as:

ntw

o

RI SR

−= = with the saturation exponent in the range [1.4-2.2].

Rt and Ro can be obtained from well logging data while the saturation exponent n is experimentally

determined in laboratory. Therefore, the in situ water saturation can be calculated by using Archie’s

equation. Based on the material balance equation, Sw + So + Sg = 1.0, the hydrocarbon reserve in place

may then be calculated.

4-1 Electrical properties system atmospheric (EPS-A) The EPS-A system is designed to measure the brine resistivity as well as core sample resistivity

determination.

Machine Description: The system includes:

♦ An atmospheric Electrical Core Holder

♦ An ambient Brine Resistivity cell

♦ A RFL meter (Fluke make)

The apparatus consists of :

1. A plastic cover which contains the electrodes and the sample during measurement.

2. Two electrodes, one fixed, one movable to enable measurements on cores of size 2" to 3".

3. A piston and integral valve to facilitate the movement and ensure repeatable contact pressure on the

electrodes.

4. Connectors and cables for connection to the RFL measuring device.

5. A special plug for connection trimming (for 1" and 1½" diameter samples)

Experiment operation

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 56

1-sample loading and unloading The first step is core sample loading in which we take a core sample from the brine and roll it once

over paper towel to remove the surface brine. Ensure that the piston is fully retracted (rotate the valve

switch command in the appropriate direction).Lye and balance the core sample on the cradle (Fig. 39).

Figure 39: Illustration of core sample loading

Then slide the platen until the sample touches the conductive pad at left side. Notice the locking pin

(Fig. 40). Topple the lid over the sample. Next slide the pin to lock the lid until the ball thrust is

engaged. If you cannot slide easily the pin, unscrew the knob by one or two turns and lock the lid.

Finally, tight the knob to ensure a good contact of the sample with the inner electrodes.

Figure 40: Illustration of system under locked pin and tighten the knob

Close the cover to prevent evaporation of the liquid from the sample. Rotate the valve in the

appropriate direction to actuate the piston jack (Fig. 41). This will cause the core sample to be firmly

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 57

held between the 2 pads. The piston is now held against the sample. Allow equilibrium conditions to be

reached and record the experiment temperature.

Figure 41: Illustration of the cover and the valve on it

After the measurement do the sample unloading and retract the conductive pad by rotating the valve

command in the appropriate direction. Open the cover and the lid over the sample. If necessary, you

can help the pads to open out by sliding the piston by hand to the far right, and then remove the core

sample. Dry the pads electrode and wetted parts thoroughly of all brine with a cloth. Repeat theses

steps for each sample.

2-Ambient condition brine cell Prior to use the core holder, constant for the brine being used must be found at actual temperature. This

is accomplished by filling the cell with brine solution of known concentration chosen to be similar to

the brine to be used in the sample test. The brine cell consists of a plastic cylinder with electrodes and

temperature probe embedded. A stop valve and a syringe allows for loading / unloading the brine. A

digital indicator displays the brine temperature. The cell electrodes can be connected to a RFL meter to

determine resistance in 4 leads pattern. Connect the power supply cord and switch button at the

back of the unit (Fig.42). Here beside is the temperature display once the unit is switched on.

Before performing any measurement, allow the unit to warm up for at least 30 minutes and to

ensure good temperature reading (Fig. 42).

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 58

Figure 42: Illustration of power supply cord and the temperature display

3- Rinsing of cell The actual brine can be incompatible with previous brine and leads to contamination or chemical

precipitation in case some previous brine remained in the cell. Hence, you must rinse thoroughly the

cell and the syringe with distilled water and empty the tubing from liquid before performing calibration

or measurement. Set the flexible tubing into the calibration brine contained in a beaker. Open the valve

(handle vertical), drive the piston down to the lower position, then lift slowly the piston to draw some

brine into the cylinder (Fig. 43). If some bubbles are generated in the cylinder, empty and refill the

cylinder until getting clear liquid. When all the electrodes are immersed in clear liquid, close the valve

(handle horizontal).

Figure 43: Illustration of rinsing of cell

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 59

4- Phase angle In addition to resistance, the phase angle will be measured to check if there was a poor contact between

the core sample and the electrodes. Good contact between the core sample and the electrodes is usually

achieved for phase angle less than 2 degrees. However, abnormal phase angle can also indicate unusual

effects such as pyrite in the core. To fix elevated phase angle and ensure good contact between the core

sample and the electrodes: reload the core and then re-measure the core sample.

5- Frequency In addition by varying the frequency, you can achieve the lower phase angle, i.e. the closer the circuit

is to a pure resistive component. The resistance value at the lowest phase angle should be

used as the actual measurement. Proceed by starting the frequency as low as possible and

increase the frequency until getting the lowest phase angle.

4-2 Electrical properties system 700 (EPS-700) This is similar to EPS-A more capabilities. This is used for overburden pressure up to 10,000 psi and

pore up to 150 psi (Fig.44).

Figure 44: Electrical properties system 700

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 60

5-Surface and interfacial tension Surface and interfacial tension of fluids result from molecular properties occurring at the surface or at

the interface of two phases. Surface tension is the tendency of a liquid to expose a minimum free

surface. Surface tension may be defined as the contractile tendency of a liquid surface exposed to

gases. The interfacial tension is a similar tendency which exists when two immiscible liquids are in

contact. In the following, interfacial tension will be denoted for both surface and interfacial tension.

Figure 45 shows a spherical cap which is subjected to interfacial tension σ around the base of the cap

and two normal pressures P1, and P2 at each point on the surface. The effect of the interfacial tension is

to reduce the size of the sphere unless it is opposed by a sufficiently great difference between

pressures, P1, and P2.

Figure 45: capillary equilibrium of a spherical cap

Young-Laplace equation for the mechanical equilibrium of an arbitrary surface is:

+=−

2112

11rr

PP σ

Where r1, and r2, are the principal radii of curvature. Introducing the mean radius of curvature defined

by 1 21/ 1/ 2 1/ 1/mr r r= + makes the Young-Laplace equation, 1 2 2 / mP P rσ− = . Note that the

phase on the concave side of the surface must have pressure P2 which is greater than the pressure P1,

on the convex side. The surface tension of a liquid surface in contact with its own vapor or with air

is found to depend only o n the nature of the liquid, and on the temperature. Usually, surface

tensions decrease as temperature increases.

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 61

Methods of Interfacial Tension measurements: There are various methods for measuring interfacial tension which have their own limitations and

applicability ranges. In this section, we will review the most common methods/techniques used for

measuring the interfacial tension.

1-Capillary Rise Method This method is based on rising of a liquid in a capillary tube and the fact that the height of the liquid,

depends on interfacial tension. Let us consider a circular tube of radius r, wetted by the liquid to be

tested. The liquid with density ρ immediately rises to a height h above the free liquid level in the

vessel (Fig. 46). The column of liquid in the capillary must be held up against the gravity pull by a

force, the so-called capillary suction. We may write the balance as:

2πrσ cos θ(capillary suction) = gρhπr2(gravity pull)

Where θ is contact angle between liquid and glass tube and g is acceleration of gravity.

Figure 46: Capillary rise method

Hence the value of σ calculated by, θθ

ρσ

cos2cos2Prhrg ∆

== where P∆ is the hydrostatic pressure of

the column of liquid in the capillary.

2-Wilhelmy Plate Method A thin plate of glass or platinum will "carry" or hold up part of liquid which is in contact with the plate.

The dynamic measurement of interfacial tension is shown in Fig. 47. In this method, the necessary

force to break the liquid film at this position will be determined as,

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 62

( )σyxWF P ++= 2

Where 2(x+y) is the contact area between the liquid and the plate, and F is the weight of the plate.

Figure 47: Wilhelmy plate methods: (a) dynamic, and (b) static method

In the static method the plate is held at the position shown in Fig. 47b and the equation will be

( ) θσ cos2 yxbWF P ++−=

Where b is buoyancy force of immersed part of the plate in the liquid and θ is contact angle.

This instrument can be calibrated such that the interfacial tension reads directly.

3-Ring Method The ring (or Nouy) method of measuring surface and interfacial tension is commonly used and the

apparatus is called a ring tensiometer. To measure interfacial tension, a platinum ring is placed in the

test liquid. The force necessary to withdraw it front the liquid is determined (Fig. 48).

Figure 48: Ring method

When the ring is completely wetted by the liquid (θ = 0), this equation is obtained from

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 63

)2(2 σπrbWF r +−=

where F is measured force, r is radius of the ring at centre (the radius of the platinum thread is

negligible compared to r), Wr is weight of the ring in air and b is buoyancy force of the ring immersed

in the liquid. For interfacial measurements, the ring is placed in the interface and the force necessary to

break the interfacial film with the ring is determined.

The instrument can be regulated in such a way that the ring weight and buoyancy effect are taken care

of with a correction factor C given by,

)2(2 rFCπ

σ =

4-Drop Weight Method The drop weight method of measuring the interfacial tension of liquid with respect to air consists in

determining the number of drops falling from a capillary. The drops are allowed to fall into a container

until enough have been collected so that the weight per drop can be determined accurately. The

principle of the method is that the size of the drop falling from a capillary tube depends on the surface

tension of the liquid (Fig. 49).

Figure 49: Drop weight method

The maximum amount of liquid W, which can hang from a capillary tube with radius r without falling

depends on the surface tension as

σπrmgW 2==

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 64

where m is the mass per drop. Observations of falling drops show that a considerable portion of the

drop (up to 40%) may remain attached to the capillary end. This effect will be compensated with a

correction factor f.

rmgfπ

σ2

=

The correction factor f varies in the region of 0.5 to 1.0. The drop method can be used for the

determination of both gas-liquid and Iiquid-liquid interfacial tensions.

5-Pendant Drop Method Small drops will tend to be spherical because surface forces depend on area. In principle, one can

determine the interface tension from measurements of the shape of the drop. In the case of the pendant

drop, the most convenient and measurable shape dependent quantity is es ddS = indicated in Fig. 50,

de is the equatorial diameter and ds is the diameter measured distance de, from the bottom of the chop.

The interfacial tension can be calculated by the following equation,

Hgd e

2ρσ =

where H is a shape determining variable. The relationship between the shape dependent quantity H and

the experimentally measured shape dependent quantity S is determined empirically. A set of 1/H versus

S values is obtained in form of tables (Table 9). The quantity of S is calculated after measuring de and

ds from shape of the pendant drop, and then 1/H can be determined from Table 9.

Figure 50: Relationship between dimensions of a pendant drop

The pendant drop method is widely used and has good accuracy.

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 65

Table 9: Values of 1/H versus S

Page 66: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 66

6-Spinning Drop

In this method, a drop of a less dense fluid is injected into a container of the denser fluid, and the whole

system is rotated as shown in Fig. 51. In the resulting centrifugal field, the drop elongates along the

axis of rotation. The interfacial tension opposes the elongation because of the increase in area and a

configuration which minimizes system free energy is reached. The method is similar to that for the

pendant drop with the gravitational acceleration g replaced by the appropriate acceleration term for a

centrifugal field.

If the fluid densities are aρ and bρ , and the angular velocity ω of rotation are known, then interfacial

tension can be calculated from the measured drop profile. When drop length is much greater than the

radius rm the following approximate expression holds

4)( 32

mBA rωρρσ

−=

Figure 51: Schematic diagram of spinning drop

The spinning drop device has been widely used in recent years to measure very low interfacial tensions.

Unlike the other methods, no contact between the fluid interface and a solid surface is required.

5-1 IFT 700 instrument The IFT 700 provides the determination of the interfacial tension, contact angle and also the

observation of heat and mass transfer phenomena. The experiment can be conducted at high pressure

(up to 69 MPa, 10000 psi) and high temperature (up to 180°C).

The flow sheet of this machine is illustrated in Fig. 52. The IFT 700LL includes basically:

• Two pressure generators (PG1 and PG2)

• Temperature indicator (TI)

• Pressure indicator (PI)

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 67

• Rupture disc and support (RD); the (safety) burst pressure is given on the plate attached to the

support. Actual burst pressure may vary by ± 5%.

• Two supply tanks for liquid (TL1, TL2).

• Capillary tubes (CT): dosage of liquid for pendant drop, type “CT-A” and another one for

standing bubble/drop, type “CT-B”, outer diameter 1/16” (1.59 mm), inner diameter 0.8 mm.

• Video system: 1 CCD camera

Figure 52: Flow sheet of IFT 700 machine

Gas-liquid systems: For generating liquid drops in gas atmosphere, the view chamber needs to be filled with the desired gas

up to the designated pressure. Therefore, the gas supply needs to be connected to valve G.

• shut all valves.

• open all suitable valves of the gas supply line (not belonging to the IFT 700).

• open G shortly and shut right away (allowing a small amount of gas to enter).

• open D for venting the system and displacing the air inside the view chamber (Purging).

• shut valve D.

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• open G carefully. Listen for whistling noises indicating escaping gas. In case of leakage,

depressurize respective part of the equipment. Fasten connection. Eventually replace damaged

pieces.

Pressure increase must be taken into account when filling the chamber prior raising the temperature.

You can fill the capillary with liquid before pressurizing the chamber to ensure that no gas is trapped in

the capillary. For this purpose, follow the dedicated instructions for filling liquid (in a separate

chapter), then open valve B while valve C is closed. The pressure generator PG1 is operated clockwise

until liquid appears at the capillary tip inside the chamber. Then close valve B and proceed to fill the

chamber with gas. Note that previous filling of the capillary or liquid being present elsewhere in the

chamber may cause fog when gas enters the view cell.

1-View cell heating A thermocouple measures the temperature inside the wall of the view cell. A second one is installed as

safety probe. In case the first thermocouple fails or breaks, the second one will prevent the system

temperature from rising excessively.

It is recommended to adjust the temperature prior to pressurizing the system.

Adjust temperature stepwise. Allow some time for temperature stabilization and watch the pressure

carefully before setting further temperature increase.

Electrical heating is fast and may overshoot the set temperature. Never exceed specified maximum

operating temperature.

Be careful when touching surfaces around the view cell: it might be very hot.

2-Filling the capillary with liquid Prior to metering liquid, and generate droplets into the view chamber, the tubing needs to be filled with

the test liquid. Proceed as follow:

• displace the lid of the liquid supply tank (TL1).

• shut the valve B.

• open the valve A (liquid inlet valve) carefully. Be aware of pressure remaining in the system!

• operate the pressure generator (PG1) clockwise to drive the piston into the chamber, until

reaching the end of stroke IN.

• fill the supply tank (TL1) with the test liquid and wait for bubbles to rise.

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• operate pressure generator PG1 anti-clockwise to withdraw the piston until reaching the end of

stroke OUT. This load the cylinder with the test liquid.

• operate pressure generator clockwise until no bubbles rise anymore at the liquid supply tank.

• Eventually drive the piston IN and OUT until the tubing is completely filled with liquid and no

gas remains trapped. Finally, withdraw the piston to the end of stroke OUT to get the cylinder

completely filled with liquid.

• shut the valve A

• open the valve C

• operate the pressure generator clockwise until the liquid is discharged through valve C. Collect

the liquid with a small glass beaker or similar.

• shut valve C.

3-Generating a Pendant Drop Allow some time for pressure and temperature stabilization.

• Operate PG1 clockwise until the pressure reading at PI1 raises up to the pressure in the view

cell read at PI2.

• Open carefully B while watching simultaneously both pressure gauges.

(If the pressure PI2 clearly drops while opening B, this means that some gas has entered the

liquid capillary tubing.)

• Operate clockwise the pressure generator PG1 until the first liquid droplet appears at the

capillary outlet.

• Once the suitable droplet is generated, close the valve B during video recording.

Liquid-liquid systems: For measuring either liquid-liquid interfacial tension by the pendant-drop method or for measuring gas-

liquid interfacial tension by the standing-bubble method, the chamber must be filled with a second

liquid in the following named “liquid C”. The liquid forming the drop is called “liquid D”. Fill the view

chamber with liquid according to the following instruction:

• Shut all valves.

• Fill the tank TL2 with liquid C: open the valve E and operate the pressure generator PG2 anti-

clockwise until the piston reaches the end of stroke OUT.

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 70

• Operate the pressure generator clockwise until no bubble rises anymore in the liquid supply

tank.

• Eventually drive the piston IN and OUT until the tubing is completely filled with liquid and no

gas remains trapped. Finally, withdraw the piston to the end of stroke OUT to get the cylinder

completely filled with liquid.

• Close the valve E.

• Open the valves F and D.

• Hold a container (glass beaker) at the outlet of the valve D.

• Operate PG2 clockwise to inject the liquid C into the view chamber until producing at valve D

outlet.

• Go on to operate PG2 clockwise, and follow liquid level in the view chamber.

• Watch for leakages inside the support.

• Close the valve D.

• Go on to operate the pressure generator PG2 clockwise until reaching the required pressure

controlled at the pressure indicator.

Note: If PG2 is easy going and no change in pressure is recorded; air may be trapped. Open the

valve D shortly for venting and restart at f.

If PG2 is increasingly hard-going but no change in pressure is recorded, look for closed valves,

or disconnected pressure indicators.

Evaluation of drop shapes pendant/sessile drop Run the program PAT by selecting “Main_PAT1-11-04_D.exe” or from the desktop shortcut to

“C/programs/PAT_exe”. The “Start- Window” appears.

The PAT software features some options especially for automatic drop generation that do not apply for

the high pressure equipment IFT-E700.

From the start window, general options can be set. For experiments using the high pressure equipment

all symbols “Check Opt.” and “Ctrl Options” should be deactivated (crossed out). This can be done

directly by clicking the mouse or by pressing the “Check/Ctrl” icon depending on the version released.

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 71

Figure 53: Start window

Select the pendant drop mode in the Start-Window when working with captured bubbles. The

“Camera” window can be selected in "portrait" or "landscape" orientation. The drop icon “Exper.”

allows for selection pendant/sessile drop or standing bubble (see Fig. 53).

The “CALIB.” icon opens the “Device Parameters” window for checking calibration of the complete

camera system. This calibration is checked automatically when starting a measurement from the main

window. Notice that the aspect ratio should be closed to 1.

Figure 54: Camera calibration

In the usual case the user carries out calibration by using the capillary (nozzle) diameter. For this

purpose, press the “PRGM” icon, choose “New/Edit” and select nozzle. Now, close the “Device

Parameters” window by clicking on “OK” and return to the start window. The position of the capillary

(nozzle) for calibrating is selected in the window opened by choosing the “FOCUS” icon.

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 72

A new window called “Focus &Light” opens containing a life image of the actual drop at the capillary

tip. This window should be checked frequently for right adjustment of light, focus and nozzle

calibration. The graph “light intensity” shows the gray values of the image ranging between 0 and 255.

The focusing marker must be positioned at the drop surface. Then, the graph shows the transition from

outside (high value=light) to inside the drop (low value = dark). By adjusting the values given in the

boxes called “white” and “black” the graph must be adjusted in order to show values of 200 – 250

outside the drop (white) and 0 – 50 inside the drop once the adjustments are completed, press “OK” to

return to the start window.

Figure 55: Illustration of the calibration method

Now, you can press the “START” button to display the main measurement window.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 73

Figure 56: Main measurement window

Measurement window and determination procedure Before starting the measurement, the experimental parameters need to be set. This includes drop phase

(internal phase) and external phase densities, the measurement procedure and the calibration

parameters. For this purpose, select “PRGM” to open the following window:

Figure 57: Profile analysis system window

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 74

Click the “New or Edit” icon to open the “Time Line” window:

Figure 58: Time line window

The time program must be set. For example T = 0.00 sec …. dT=1.0, which means that starting at 0

seconds a measurement is carried out every second. With the high pressure equipment “CONTROL

Vol/Area” is not applicable. The “CALIBR.” cursor must be switched toward “NOZ.”

(nozzle/capillary).

Settings can be saved or loaded as ~.prg files. By choosing “Done” you can return to the parameter

window. After having chosen a file name to save the image data (~.prf), the parameter window is

closed and the main window appears once you click “OK”. Now, you can start the measurement by

selecting “START”. The calibration data is used during the interfacial tension determination. (Fig. 58)

The diagrams in the lower part of this window show the interfacial tension (as a rough estimate) and

the drop area in real time. These data are given for information only and are not saved.

A small picture at the right side of the life drop image named “Drop Dim.” Indicates whether the drop

has a suitable dimension (green) or is too small (red) for determination of the interfacial tension.

The symbol below named “Ctrl Loop” is not applicable with the high pressure equipment and should

be switched off.

Page 75: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 75

Figure 59: Illustration of determination procedure

The data acquisition in the “Main Measurement” window is stopped by pressing the “ABORT” button.

Afterwards, press “EXIT”. In case “Fitting Auto-Start” was switched on in the “Experimental

Parameter” window, the fitting procedure starts automatically. Otherwise, press “FITTING” in the

start window.

Press “LOAD” in the appearing “Fitting” window and select the ~.prf file containing the data of an

experiment performed earlier. All the available measurement points are computed to match the Laplace

equation, and then to determine the interfacial tension as a function of time. Data of the interfacial

tension, the drop volume and area etc. are saved in a ~.fit file to the hard disk. This file can be imported

to an excel sheet.

However, students should consider the following safty notices:

• Operation and maintenance may only be carried out after all necessary steps have been taken to

ensure the safety of people and equipment.

• Make sure that samples involved (liquids, gases, fluids and solids) do not interact with parts of

the equipment to which they are in contact.

• Aggressive organic solvents, e.g. aromatic substances can lead to a leakage in the view cell.

Page 76: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 76

• Handling highly volatile or toxic liquids requires suitable ventilation.

• Working at high pressure requires wearing safety glasses.

Calculation and Report: Use the notations given in Fig. 60 along with the following equations to fill Table 10.

HgDe

2ρσ

Λ= where g=981 cm/s2, and De (real size of de) = de (1.1/ d IMG), mm

Figure 60: pendant drop imaging picture

Table 10: Data sheet for IFT 700 experiment

1ρ 2ρ ρ∆ Image Picture Sizes Sample de

( mm)

ds

( mm) dIMG

( mm)

Page 77: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 77

6-Capillary pressure The coexistence of two or more immiscible fluids within the voids of a porous medium, such as a

reservoir rock, gives rise to capillary forces. As interfacial tension exists on the boundary between two

immiscible fluids in a pore space, the interface is curved and there is a pressure difference across the

interface. The pressure difference is termed the capillary pressure and can be expressed as:

PC = Po - Pw

where:

Po is the oil pressure (non-wetting phase)

Pw is the brine pressure (wetting phase)

Capillary pressure as a function of surface tension and radii of curvature r (for spherical cap) is,

( ) 2 coswoc w oP gh

rσ θ

ρ ρ= − =

Note that the free water level, FWL is the point where Pc=0. Oil-water contact OWC above FWL has

Sw=100% due to the capillary action. The zone of varying water saturation with height above OWC is

called the transition zone (Fig. 61).

Figure 61: Illustration of saturation distribution above OWC

The size of the transition zone depends on pore size distribution (PSD), grain sorting, interfacial

tension, rock characteristics (porosity/permeability) and also difference in fluid density. The saturation

Page 78: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 78

history of the rock can also affect the capillary pressure. Two processes usually considered are

drainage which is the replacement of the wetting phase (e.g. water) with non wet phase (saturation of

wet phase decreases). In this case, the saturation level is dictated by the capillary pressure associated

with the narrow pores and it is able to maintain water saturation in the large pore below. The second is

imbibition where wetting phase saturation increases by the expulsion of the non wet phase. The level

of saturation is determined by the large pore reducing the capillary pressure effect and preventing

water entering the larger pore. Figure 62 shows different process of this kind in a water wet system

where A, B, C shows respectively the primary, negative secondary and positive secondary drainage and

D and E shows positive and negative imbibition respectively.

Figure 62: Typical capillary pressures for in various stages of drainage and imbibition processes

Capillary pressure measurements are essential for the complete characterization of a hydrocarbon

reservoir. A plot of capillary pressure versus fluid saturation for a core plug can be used:

• to calculate reserves

• in reservoir simulation computer routines

• provides data on the irreducible water saturation of a reservoir rock

• shows the entry pressure of fluid into a water saturated reservoir or cap rock.

6-1 CAPRI instrument The The CAPRI system is dedicated to the determination of the capillary pressure curves (positive

and negative) and the electrical resistivity index as a function of core sample saturation at reservoir

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 79

conditions. Knowledge of the water-oil capillary pressure and resistivity index vs. saturation

relationship is necessary for many reservoir-engineering tasks:

(1) assess connate water saturation to calculate oil in place;

(2) calibrate resistivity logs;

(3) determine the height of the transition zone;

(4) model oil displacement either by free water imbibition and /or water injection.

The equipment measures the resistivity of core plugs at different brine saturations by a precise

resistivity meter having 4 electrode measurement system. The core plug is placed in a core holder

subjected to confining pressure and pore pressure equivalent to reservoir conditions. Temperature of

the core plug is raised to the reservoir condition. The brine saturation is changed from 100 % to lower

values by gradually increasing the pressure of an upstream metering pump which injects oil into the

core plug and displace the brine. The volume of the displaced brine is accurately determined by a

downstream metering pump which accumulates the displaced brine at a constant pressure. Both the

pumps are attached to the core holder through semi porous membrane saturated with respective fluid.

The resistivity of the pure brine used for the saturation of the core plug is determined with the help of a

Rw cell subjected to the reservoir pressure and temperature condition. The resistivity measurement of

a core plug at 100% brine allows for the evaluation of the Formation Factor (FF) whereas the

resistivity of a core sample at different saturations allows for the determination of the Resistivity Index

(RI) at simulated reservoir pressure and temperature conditions. The equipment has also the provision

for estimation of Resistivity of brine (Rw) at simulated reservoir temperature and pressure condition.

The user can run tests either in manual mode or in sequenced mode. In automatic mode, the operator

fills a table of pressure increments. Test data is graphically displayed on the screen and is logged on the

hard disk as a table file. Printouts of the input and test data are done using a printer.

Machine Description Sample Diameter 1” or 1” ½ or 30 mm (according to customer’s selection)

Sample Length from 2" to 3"

Sample: Square edge, Parallel faces and consolidated

Pressure:

Overburden: up to 10,000 psi

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 80

Pore: up to 9,000 psi

Capillary pressure: up to 150 psi

Ceramic pressure breakthrough: 150 psi

Temperature: ambient up to 150°C

A schematic connection diagram is shown in Fig. 63.

Figure 63: A schematic connection diagram of CAPRI instrument

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 81

Experiment operation: During the test, the temperature of the core plug is raised to the reservoir condition. The brine

saturation is changed from 100 % to lower values by gradually increasing the pressure of an upstream

metering pump which injects oil into the core plug and displaces the brine. The volume of the displaced

brine is accurately determined by a downstream metering pump which accumulates the displaced brine

at a constant pressure. Both the pumps are attached to the core holder through semi porous membrane

saturated with respective fluid. For this the following is done.

After setting up the core holder, the first step is to fill the pumps. This can be done through the panel

available in the software. Note that the pumps should be calibrated so that the volumes shown on the

panel is the true one. At the next step it is time to give the core holder some confining pressure. An

starting pressure on 500 psi should be sufficient. It is highly recommended that before any process the

air probably contained within the core holder and the pumps are removed. This should be done for the

three pressures. The two filled pumps then should be started one at each time with almost the same

pressure in order to make sure the core is intimately saturated with the fluids. The pressure of oil pump

is a little less then the brine pressure so that no flow into core occurs.

When all the steps are performed correctly it is time to start the test. The brine pump is always on and

the run mode is pressure. In this case the brine pressure is set to some value. The set mode on oil pump

is delta pressure and the test begins by setting a small delta pressure. It is good to check to see if the

delta pressure shown by the software is calculated correctly. The first steps of changing the delta

pressure should be done by care cause it might affect the accuracy of the result curve. The steps are

changed if the resistivity has become constant or if the displaced volumes of oil and brine pumps are

showing the same value. At the end of the experiment decrease the pore pressure by setting the water

pump in constant pressure with 15 psi set value with a pressure ramp of -50 psi/min and the oil pump in

constant delta pressure at zero psi set value. As the pore pressure decreases, the confining pressure by

opening slowly the isolating confining valve. Keep a difference of 300 psi between the confining

pressure and the pore pressure and decrease the temperature to room condition.

The process body is schematically composed of 5 stages. The end of a step is determined from

stabilisation of electrical measurement and volume in the pumps. Water pump is pressure controlled at

pore pressure set point. Oil pump is DeltaP controlled at capillary pressure.

Page 82: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 82

1. Starting from a sample 100% saturated with brine, Primary drainage is applied by increasing

DeltaP in small steps. DeltaP is going positive. The maximum final DP can be 150 psi. Practically,

the drainage is completed when no more water production happens for an increase in DeltaP. Each

step can need from a few hours up to several days to reach equilibrium. When reaching equilibrium,

DP and pumps volume are recorded. From the reading of the pumps volume, the balance with the

sample content ("saturation" in oil and water) is determined. The DeltaP is the capillary pressure. A

graph can be plot of DeltaP vs water saturation.

2. Spontaneous imbibition is then conducted by reducing DeltaP in small steps, down to DeltaP

equal zero. There is an hysterisis, and the curve of DeltaP vs water saturation is different from the

curve obtained before. The saturation curve does not cross the pressure axis at for 100% water.

3. Going further, we run the Forced imbibition by reducing DeltaP in small steps, getting negative

values of DeltaP. The maximum final DeltaP can be -150 psi (theoretical value). Practically, the

imbibition is completed when no more water enters the sample for a change in DeltaP.

4. In the next step, we increase DeltaP by steps during Spontaneous drainage, until DeltaP is back

again to zero. There is an hysterisis, and the curve of DeltaP vs water saturation is different from

the curve obtained at previous stage.

5. Going on to increase DeltaP in positive value, we run the Secondary drainage. DeltaP is build up to

the previous maximum value during Primary drainage.

The process schematic to get whole pc curve is shown in Fig. 64.

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Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 83

Figure 64: Schematic illustration of various stages of the process of getting whole pc curve

Calculations and Report: The type of summarized information along with the formation factor results obtained from CAPRI is

shown in Fig. 65. Note: the core holder factor refers to the sample size 1" ½; with electrodes spaced

by 25.4mm (2 / 4

25.4 1000dm π

=× ). In red are the experimental data, in black are the calculated values.

Page 84: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 84

Figure 65: Summarized report of the formation factor results obtained from CAPRI

The type of report of Pc, Ir and n with core partially or totally desaturated is shown in Fig. 66.

Figure 66: A typical summarized report of Pc, Ir and n of a core partially or totally desaturated

Page 85: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 85

The equation used to calculate the parameters are shown in Fig. 67.

Figure 67: Illustration of equations used to calculate the parameters in CAPRI instrument

Moreover, a typical capillary pressure curve obtained is shown in Fig. 68.

PC curve

-5000

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 10 20 30 40 50 60 70 80 90 100

Brine Saturation (Sw), %PV

Cap

illar

y Pr

essu

re (P

o - P

w),

mba

r

Figure 68: Illustration of a typical capillary pressure curve obtained from CPAR instrument

Page 86: Core Lab New

Reservoir Rock Properties Analysis, Mohsen Masihi

Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 86

7-Permeability Permeability is a property of a porous medium which shows the ability of porous media to

transmit fluids. The reciprocal of permeability represents the viscous resistivity. The effective

permeability of a porous medium is a measure of the rock conductivity to a particular phase of a multi-

phase fluid system residing within the porous medium, where the saturation of each phase is specified.

Relative permeability is the ratio of the effective permeability of a particular fluid phase to some

arbitrary reference permeability (i.e. absolute permeability). Permeability has the unit of m2 in SI

system or Darcy in field unit with a conversion factor of -12 21D 0.986923 10 m≡ × . Note that a rock

sample has a permeability of one meter squared when it permits 1 m3/s of fluid of 1 Pa.s viscosity

through an area of 1 m2 under a pressure gradient of 1 Pa/m. Permeability is calculated using the

following equation:

Where:

k = permeability (Darcy)

q = flow rate (cm3/S)

= viscosity (mPa.s)

x = length (cm)

A = cross sectional area (cm2)

p = differential pressure across flow section (atm).

One of the quick methods to measure permeability is the “transient method”, which is used in KeyPhi

device. Transient measurements employ fixed-volume reservoirs for the gas. These may be located

upstream of the sample from which the gas flows into the sample being measured. The pressure falloff

apparatus (Fig. 69) employs an upstream gas manifold that is attached to a sample holder capable of

applying hydrostatic stresses to a cylindrical plug of diameter D and length L. An upstream gas

reservoir of calibrated volume can be connected to the calibrated manifold volume by means of a valve.

Page 87: Core Lab New

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Department of Chemical & Petroleum Engineering, Sharif University of Technology, Tehran, IRAN 87

Figure 69: schematic of pressure-falloff gas Permeameter.

Multiple reservoir volumes are used to accommodate a wide range of permeabilities. The

downstream end of the sample is vented to atmospheric pressure. An accurate pressure transducer is

connected to the manifold immediately upstream of the sample holder. The reservoir, manifold and

sample are filled with gas. After a few seconds for thermal equilibrium, the outlet valve is opened to

initiate the pressure transient. When the upstream pressure has decayed to about 85% of the fill

pressure, data collection is started. Pressures and times are recorded. This technique has a useful

permeability range of 0.001 to 20,000 md.

The use of liquids for permeability measurements eliminates the problem of gas slippage, and at

reasonable and usual flow rates, inertial resistance is generally negligible. Thus, Darcy’s Law can be

used directly to calculate permeability from a single flow rate measurement. However, potential

permeability alteration from interaction of rock constituents and liquids (especially aqueous solutions),

fines movement, and microbial plugging requires special attention. Also, the liquid remaining in a

sample may have to be removed before other measurements can be performed. Because of these

problems, most routine permeability measurements have been made using gases. However, for some

samples, such as those sensitive to drying techniques, liquid permeability measurements are considered

to be the only acceptable alternative. BRP-350 is a device which can be used for absolute and relative

permeability measurement using both gas and liquids. The description of this instrument is given in

section 7.2.

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Klinkenberg effect: Klinkenberg (1941) has reported that there are variations in the permeability determined by using gases

as the flowing fluid compared to those obtained when using liquids. This has the following relation,

L

1

g

m

kk

bP

=

+

where Pm is the mean pressure, kg is the gas permeability and kL is the equivalent liquid permeability.

These variations were considered to be due to slippage, a phenomenon well known with respect to gas

flow in capillary tubes. The phenomenon of gas slippage occurs when the diameter of the capillary

openings approach the mean free path of the gas. Note that the mean free path of a gas is a function of

molecular size and the kinetic energy of the gas. Therefore, permeability of gas depends on factors

which influence the mean free path, such as temperature, pressure and the molecular size of the gas.

Figure 70 is a plot of the permeability of a porous medium as determined at various mean pressures

using three different gases. Note that for each gas a straight line is obtained for the observed

permeability as a function of the reciprocal of the mean pressure of the test. All the lines when

extrapolated to infinite mean pressure (1/Pm = 0) intercept to the same point kL.

Figure 70: Variation in gas permeability with mean pressure and type of gas

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7-1 KeyPhi instrument As described before KEYPHI instrument is able to measure directly the gas permeability as well as

calculating important parameters such as Klinkenberg slip factor "b", Klinkenberg corrected

permeability and Inertial coefficient. The gas permeability determination is based on the unsteady state

method (pressure falloff ). As can be seen in Table 8 the range of permeability measurement is from

0.001 md to more than 20d.

The detail conditionings and the operation procedures are as those described in chapter 3 (porosity).

7-2 Benchtop Relative Permeameter (BRP 350) The Benchtop Relative Permeameter system is designed to perform tests on core plug samples

in order to determine monophasic permeability, liquid/liquid relative permeability and optionally

liquid/gas relative permeability.

The determination of relative permeability allows comparison of the different abilities of fluids to flow

in the presence of each other. In many instances, relative permeability data selected to represent the

subsurface of reservoir fluid behavior have more effect on the ultimate answer than any other

parameter used in reservoir engineering equations.

These tests are performed at ambient temperature with the unsteady-state technique. Confining

and pore pressure can go up to 350 bars (5000 psi) maximum. All wetted components are made of

Stainless Steel 316 for chemical compatibility and corrosion resistance. This system includes a fluid

delivery pump, 2 piston accumulators, a core-holder, a back pressure regulator, a confining pressure

system, a pressure measurement system, and optionally a video tracker and a gas meter. Operation of

the system is controlled through a computer interface. The Applilab software included with the system

is designed to allow for automated data acquisition and pump control. Finally, the Cydar software

enables calculation of relative permeability. Table 15: General properties of BPR 350 instrument.

Working Confining Pressure Up to 5000 psi (option 10000 psi)

Working Pore Pressure Up to 5000 psi (option 10000 psi)

Core Sample Diameter 1’’ (option 1.5’’)

Core Sample Length 1’’ to 3’’

Confining Pump Pressure Up to 10000 psi

Video Tracker burette External Diameter 18.00 mm

Gas Meter Capacity per Revolution 250 cc

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Working Procedure The Applilab software has been developed by the programmers from VINCI in order to control the

process parameters simultaneously from one central unit. The graphical interface of Applilab is shown

below.

Figure 71: The graphical interface of the Applilab software.

Applilab allows to:

Ø Switch on/off the pump (A)

Ø Control the flow rate of the pump (A)

Ø Display the set parameters (pressure, volume,...) during remote control (B)

Ø Show the evolution of process graphically by trends display (C)

Ø Offset the pressure sensors (D)

Ø Log data (E)

Dead Volume Measurement The dead volume should be measured using a specific caliber, by the following procedure:

A

C

D

B

E

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1. Check that the caliber is mounted on the core holder. Saturate the tubing from the oil

accumulator to the core holder with oil. Then inject brine to saturate all the lines until the

burette with brine. Refer to the above picture to open/close the burette valves.

2. Inject oil (drainage) and simultaneously open the top burette valve and close the bottom burette

valve. When only oil is produced in the burette, measure the Volume of water produced. The

first drainage dead volume is equal to this volume minus the caliber void volume, i.e. 0.1 cc.

3. Inject brine (imbibition) and simultaneously close the top burette valve and open the bottom

burette valve. When only brine is produced in the burette, measure the Volume of oil produced.

The first imbibition dead volume is equal to this volume minus the caliber void volume, i.e. 0.1

cc.

4. Repeat the same operations until getting the same volumes (typically after 3 or 4 cycles). Dead

volume measurements for gas-liquid experiments are similar except that gas is injected instead

of brine.

Figure 72: Hydraulic schematic of the assembly with a caliber sample.

Preparation of the Test In order to perform any test using BPR 350, the following steps should be done carefully.

1. Select a suitable core sample Select a homogeneous core with square edges and parallel faces. Make sure that the length is greater

than 24 mm and smaller than 77 mm. (Write down all information about the core, especially the length,

diameter, dry weight and gas permeability. Then saturate the core with brine in case of liquid-liquid

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permeability, or oil in case of gas-liquid permeability. The saturation of the core can be done with a

saturator or with a vacuum bell connected to a vacuum pump. Then write down the wetted weight.)

2. Load the sample in the core-holder

3. Initiate the confining pressure Close the hand pump release valve. Open the confining valve HV06 and close the buffer valve HV08.

Operate the handle to increase the pressure up to around 700 psi. If needed, you can decrease the

pressure by opening the hand pump release valve. Close the confining valve HV06. Wait for stability

and adjust if necessary.

4. Initiate the back pressure Set the nitrogen pressure at your facility to around 250 psi, open back pressure valve HV07 and close

buffer valve HV08. Wait until back pressure reaches roughly 200 psi. If needed, you can decrease the

pressure by opening buffer valve HV08 and opening the hand pump release valve. When the set point

pressure is reached, close back pressure valve HV07 and close buffer valve HV08.

5. Purge the lines Before performing a test, you have to ensure that the inlet and outlet lines are correctly saturated and

that no gas is remaining in these lines. For the following explanations, refer to the below picture

concerning the mentioned numbers.

6. Pressure Control Open process valve HV01, open brine valve HV03 and close oil valve HV02. Start injection pump and

control that outlet pressure increases up to back pressure. Wait until inlet and outlet pressure are

stabilized.

At any time you must control the following relations true:

Back P < Outlet P < Inlet P < Confining P < 5000 psi

In the case Inlet P > Confining P, you can spoil the core by getting invasion of confining oil into the

core sample. Typically, Back P = 200 psi and Confining P = 700 psi.

I. Monophasic Permeability Once the different steps to prepare a test are realized, you can start the monophasic permeability

measurement. Refer to Darcy’s law for permeability calculation. Darcy’s law can be applied under the

following assumptions:

Ø The core plug is 100% saturated with the flowing fluid.

Ø The flowing fluid is incompressible.

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Ø The flow is horizontal, steady state and under the laminar regime.

Ø The flow of fluid through the porous medium takes place under viscous regime (i.e. the rate of flow is sufficiently low so that it is directly proportional to the pressure differential or the hydraulic gradient).

Ø The flowing fluid does not react with the porous medium because it may alter the characteristics of the porous medium thereby changing its permeability as flow continues.

Once the system is stabilized you can run brine injections at different flow rates. For each flow rate,

wait stabilization of the ΔP and complete the excel file “Permeability-template” provided with the

Applilab software as in the below picture.

Figure 73: software excel sheet during a monophasic permeability measurement.

On this excel sheet, monophasic permeability is automatically calculated once the data cells are filled.

II. Relative Permeability The gas, oil and water relative permeabilities are normally denoted by Krg, Kro and Krw, respectively.

Relative permeabilities are usually expressed by the ratio of effective permeability to absolute

permeability. Effective permeability is a relative measure of the conductance of the porous medium for

one fluid phase when the medium is saturated with multiple fluid phases. Absolute permeability can be

expressed as monophasic permeability or usually the effective oil permeability at irreducible water

saturation.

The Unsteady State Method for relative permeability is based on the Buckley-Leverett two phases flow

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model. This model can be applied under the following assumptions:

Ø Immiscible and uncompressible fluids

Ø No capillary pressure

Ø No gravity

Ø Unidirectional flow along the core axe. Preparation of the diphasic test

Ø Adjust the camera to the fluid interface. Use the video tracker software to calibrate the volume

and detect the interface.

Ø Turn the ΔP valve HV05 on bypass position. Then offset the ΔP thanks to the Applilab

software. Make sure that the actual Delta P is within the transmitter range (0-500 psi), then turn

the ΔP valve HV05 on measure position.

Ø Start data logging. You can adjust the time interval to your needs.

a) Oil injection (Drainage)

Reset the camera volume thanks to the Applilab software. Run the injection pump at medium flow rate

(example: 0.5 cc/min) and simultaneously open oil valve HV02 and close brine valve HV03. Refer to

the below picture concerning the position of the burette valves. Wait until ΔP and Vw stabilization.

Then complete the excel file “Permeability-template” provided with the Applilab software, especially

the “Drainage” part. From the pump flow rate, ΔP and Vw, the excel file will calculate automatically

the initial water saturation (Swi) and the permeability of oil at Swi, i.e. Ko(Swi).

Figure 74: Drainage configuration.

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b) Brine injection (Imbibition)

When the drainage is over, i.e. the ΔP and Vw are stabilized, you can prepare the imbibition. This is the

most important phase of the test. Before injecting brine, check the following points:

Ø Decrease the flow rate of the pump (example: 0.1 cc/min).

Ø Check that historical collect is running.

Ø Reset the camera volume thanks to the Applilab software.

Ø Offset the ΔP (refer to section 3.7).

Then do the following operations simultaneously:

Ø Start the Applilab chronometer

Ø Close oil valve HV02

Ø Open water valve HV03

Ø Close the top burette valve

Ø Open the bottom burette valve

Ø Write down the imbibition start time

Figure 75: Imbibition configuration.

On Applilab trend curves, you can control the evolution of the ΔP and oil production. The typical shape

of these curves is shown in the below picture.

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Figure 76: Typical curves for Delta P and Oil Production.

Stabilization usually occurs after 5 pore volume injections. Now, we can proceed to the treatment of

data to calculate the relative permeability curves using CYDAR software.

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8- Other Rock Properties

8-1 Acoustic Velocity System (AVS 700)

The measurement of the speed of sound through a rock yields an index called velocity. This velocity

depends upon both the elastic modulus and density of the rock. If the rock is isotropic, homogeneous

and linearly elastic then there are only two possible types of waves which can travel through the rock:

o a compressional, acoustic or sonic wave,

o a shear wave.

Vinci Technologies’ AVS 700 measure both compressional (Vp) and shear wave (Vs) velocities in the

borehole which are used to calculate Young’s modulus and Poisson’s ratio required in hydraulic

fracture design, to detect hydrocarbons and to estimate formation porosity.

Seismic exploration uses both compressional and shear waves to define and map reservoir boundaries,

detect hydrocarbons in place and monitor changes during production (4D-seismic reservoir

management). These technologies have the attractive feature of mapping petrophysical and fluid

variations on the scale of the reservoir. Elastic properties, moduli and velocities are also used to model

reservoir subsidence and assess borehole stability and sanding potential.

AVS 700 uses high frequency signals. To calculate velocities one then divides the sample length (m)

by the travel time (sec) to arrive at a velocity in m/sec. The speed of the P-wave is about twice that of

S-wave. The ramifications of this are that the shear wave arrives amidst reverberations of the earlier P-

wave making its detection more difficult.

AVS 700 uses transducers on both sides of the core. One transducer acts as a source and at the opposite

end, a second acts as a receiver.

Figure 77: General schematic of the AVS parts.

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AVS 700 uses three piezoelectric crystals. The crystals generate:

o Compressional wave (P)

o Polarized shear waves (S1 and S2)

The shear waves are orthogonally polarized. A matched set of transducers acts as a receiver array.

Transducers are activated such that five waveforms can be recorded at each pressure point. The five

waveforms are:

1) P wave;

2) S wave (S1 transmits and S1 receives)

3) S wave (S2 transmits and S2 receives)

4) S wave (S1 transmits and S2 receives)

5) S wave (S2 transmits and S1 receives)

If a material is isotropic, then there should be no signal recorded on the cross coupled transmitter /

receiver pairs. Signal is a positive indication of anisotropy. If a material is isotropic, then the signals

recorded on S1 and S2 should be equivalent. A difference between S1 and S2 signals shows the

anisotropy of the sample. If a rock is isotropic and linearly elastic then one can relate the velocities and

moduli through the following relationships:

Where:

VP: Velocity of P wave (in m/s)

VS: Velocity of S wave (in m/s)

ρ: Density (in kg/m3)

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ν: Poison’s ratio

E: Young’s modulus (in Pa)

K: Bulk modulus (in Pa)

μ: Shear modulus (in Pa)

λ: Lame’s constant (in Pa)

K: Compressibility (in Pa−1)

Al: Acoustic impedance (in kg·m−2·s−1)

Operational Parts

1. Core Holder AVS is provided with two core holders one to accommodate plugs of 1’’ diameter and one to

accommodate plugs of 1.5’’ diameter. The core holders are tri-axial and can accommodate cores of 1 to

3’’ length. It is made of stainless steel. Radial pressure, Axial pressure and Pore pressure can be applied

independently. The design of the vessel is so that when Radial and Axial pressures are identical the

core holder is hydrostatic.

The different elements of the vessel are shown on the pictures below. The main features of the device

are as follows:

o Core diameter: 1 & 1.5”

o Core length: 1 to 3”

o Material: stainless steel

o Pore pressure: up to 10,000 psi

o Confining pressure: up to 10,000 psi

o Radial pressure: up to 10,000 psi

The scheme below shows the 1.5’’ core holder.

Figure 78: Different elements of the vessel.

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2. Accumulator AVS includes a 100 cc pore fluid accumulator. This accumulator is connected to the hand pump and

permits to apply a pore pressure up to 10,000 psi. The accumulator is located on the rear side of the

panel. The process fluid is on the top side of the accumulator.

The accumulator is isolated on the pump side by the valve V5 and on the process side by the valve V1.

Figure 79: The fluid accumulator.

3. Electrical Connections The connections between the acoustic core holder, the switch box, the impulser and the oscilloscope

are shown below. The Oscilloscope is connected to the impulser via 2 BNC female / female cables. The

impulser is connected to the Switch box via 2 BNC female / female cables. The switch box is

connected to the core holder via 6 SMA male to BNC female cables.

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Figure 80: Type of connections between different parts.

Measurement 1. Overburden Set-up

1.1. Building up step by step procedure o Check the connection from the panel ports RADIAL and AXIAL to the core holder.

o Open Valve 3 “RADIAL INLET” and Valve 4 “AXIAL INLET".

o Check the oil level in the manual pump. Refill if necessary with specific oil (refer to specific

manual).

o Check the built-in valve of the manual pump: it must be closed.

o Operate the pump to build up the pressure in both radial and axial direction.

o Check the pressure on the 2 dedicated displays: upper central for RADIAL, upper right for

AXIAL.

o Optionally, close Valve 3 RADIAL INLET and operate the pump to build-up more axial

pressure.

o Once you have reached the axial and radial pressure, close Valve 3 and Valve 4 to isolate the

pump.

o When building up the process fluid pressure, it may interact with the axial and radial pressure.

Adjust them if necessary.

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1.2. Pressure Release o Before relieving the radial or the axial pressure, be sure to open the build-in valve of the manual

pump. Then, relieve the radial / axial pressure by opening the Valve ¾.

o Do not forget to close the build-in valve of the manual pump if you need to increase the axial

or/and radial pressure.

o Always check the pressure at RADIAL and AXIAL displays.

2. Transducers’ Orientation Whatever the relative positions of the transducers are, the signal of the P-waves displayed on the

oscilloscope should remain constant. The intensity of the signal of S waves should be maximum when

S1 transducers are parallel. If this is not the case, it means that the core is anisotropic (refer to the

“Theory” chapter). To adjust the relative positions of the transducers, the operator may rotate them

thanks to the tube guides H02-213 (long) and H02-224 (short).

The correct position is determined by a constant checking of the oscilloscope signal.

Figure 81: Adjusting the relative position of the transducers.

3. Time of Flight Determination The “time of flight” is the duration between the emission of the signal by one transducer and the

reception of this signal by another one. at the opposite end of the core. This time of flight should be

corrected since it includes the propagation in the core itself but also in the spreader (see Chapter

“Calibration”).

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3.1. P Waves Using an oscilloscope, calculating the time of flight of P-waves is very easy. It is possible to trig the

signal of the impulse. The time of flight is the difference between the pulse and the first detected signal

following the pulse. On the following screen copies, the time of flight of P-waves is of about 28.6 μs.

Figure 82: Schematic screen showing a P-wave time.

3.2. S Waves Calculating the time of flight of S waves is far more difficult than the one of P waves. S-waves will

generate P waves each time they encounter an interface (transducer /spreader, speader/core,

core/sleeve, etc.). Since the velocity of P waves is about twice as much as the one of S waves, the P

waves will reach the receiving transducer before the S-waves and blur the signal. The amplitude of the

unwanted P waves is usually lower than the one of the S waves. Another possible way to discriminate P

waves and S waves is to slightly modify the relative positions of the transducers. The amplitude of P

waves should remain almost constant while the amplitude of S waves should decrease. On the

following screen copies, the time of flight of S-waves is of about 42. μs.

Figure 83: Schematic screen showing a S-wave time.

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4. Calibration The instrument is provided with some calibration plugs: Two aluminum plugs of 1.5’’ diameter (1 and

3’’ of length respectively) and two nylon plugs of 1.5’’ diameter (1 and 3’’ of length respectively).

Those plugs can be used to calibrate the AVS system and to get the propagation

speed of S and P waves via the time of flight of those waves. The table below gives the propagation

speed of P and S waves in aluminum and nylon at ambient temperature.

Parameter Aluminium Nylon

Propagation speed of P waves (m/s) 6300 2700

Propagation speed of S waves (m/s) 3100 1700

The propagation speed of P and S waves can be calculated via the following equations:

With:

VPwave & VSwave : Propagation speed of P/S waves (m/s)

TPwave & TSwave : Time of flight of P/S waves (s)

CFPwave & CFSwave : Correction factor of P/S waves (s)

The correction factors correspond to the time of flight of the waves without any plug. They can be

directly measured by pressing the two spreaders one against each other. To get an accurate

measurement of those correction factors it is possible to measure the time of flight of the waves in a

calibration plug. Thus the correction factor can be calculated using the equations below:

The calibration factors of the AVS system should be of about 10 μs for P waves and 16 μs for S waves.

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References and further reading