docx
THE CORRELATION BETWEEN POROSITY, SATURATION, PERMEABILITY AND
ACID SOLUTIBILITY ON CORE SAMPLES OF LIMESTONE ROCKS IN THE
KEMADANG AREAKorea National Oil Team
AbstractPetrophysics is the study of rock properties and their
interactions with fluids (gases, liquid hydrocarbons, and aqueous
solutions). The geologic material forming a reservoir for the
accumulation of hydrocarbons in the subsurface must contain a
three-dimensional network of interconnected pores in order to store
the fluids and allow for their movement within the reservoir. Thus
the porosity of the reservoir rocks and their permeability are the
most fundamental physical properties with respect to the storage
and transmission of fluidsRock core analysis in the laboratory is
used to determine the petrophysical properties of rocks. Rock core
analysis procedure basically consists of two parts, they are
routine rock core analysis and special rock core analysis. Routine
rock core analysis porosity in general is about porosity
measurement, absolute permeability measurement and fluid saturation
measurement. Whereas special rock core analysis can be grouped into
two, they are the measurements in static condition and measurements
in dynamic conditions. Measurements in static conditions including
capillary pressure, electrical properties and the speed of sound
propagation, grain density, wettability, rock compressibility,
permeability and porosity function of pressure (net over burden)
and petrographic studies. And the measurements on dynamic
conditions include: the relative permeability, thermal recovery,
residual gas, water flood evaluations, liquid permeability
(completion evaluation, work-over and the injection fluid includes
surfactant and polymer).From the laboratory experiments that we
did, there is the some results. The are measurements of porosity,
permeability, saturation, acid solutibility of formation samples.
Core that we used for research was limestone because limestone is a
carbonate rock that will react with acid, and it is also porous
rock according to the physical properties of reservoir rocks in the
field. We took that core in the Wonosari area, because Wonosari is
an area of limestone mountains.
Keywords : Porosity, Saturation, Permeability, Acidizing.1.
PREFACE1.1. Background Issues Rock core analysis is the analysis
steps after core sampel of formation in the subsurface, obtained in
which the purpose of the rock core analysis is to determine
directly the information of the physical properties of rocks to be
carried out exploration. Core analysis is divided into two
activities, The are Routine Core Anaysis and Special Core Analysis.
Routine Core Analysis include the measurement of porosity,
saturation and permeability. Porosity measurements or samples of
reservoir rocks is to know the size of the cavity in the rock by
rock bulk volume and pore volume of the rock. Measurement of Fluid
Saturation aim to determine the pore space of reservoir rocks
containing fluid especially oil. Permeability measurements to
determine the ability of a fluid reservoir rocks passed without
damaging the structure of the constituent rocks. Determination of
Levels of Sample Solution Formation in Acid Solution, determine the
concentration of acid-soluble formations in solution, in order to
obtain important information prior to stimulation.
1.2. Methodology The method used to determine the porosity is
Mercury Method Injection Pump, with materials used Hg or mercury as
a guide. It is also used weighing method. But we only use the
weighing method. The method used for the measurement of saturation
is a method of distillation and retort method. But this time only
just introduced distillation method. To determine the permeability
of a reservoir rock that is supported by a tool consisting of a
liquid permeameter permeameter and gas permeameter. This tool can
only identify a single fluid, the rest of this tool can not be
read. For samples soluble levels, we calculate the solubility as%
by weight and material dissolved in 5N HCl. In experiments sieve
analysis, we determined the type of screen or filter to be used to
fix the sand problem.
2. THEORETICAL 2.1. Porosity Discussed from the point of
reservoir engineering, porosity divided into two, namely: Absolute
porosity, defined as the ratio between the whole pore volume to the
total volume of rock, or can be written:
abs=Vp/Vbx100%........................ (1)
abs = (Vb-Vg)/Vb x 100 % .......... (2)
Vp = volume of rock pores, cm3 Vb = the total rock volume, cm3
Vg = volume of grain, cm3
Effective porosity, defined as the ratio of the pore volume is
related to the total volume of rock or written:
eff = (Vp related)/Vb x 100 % .... (3)
Therefore, the oil can only flow through interconnected pores.
So that is important in the petroleum industry and that we measured
in this experiment is the effective porosity. In general, the
amount of porosity ranging between 5-30%. Theoretically, the
magnitude of the porosity of not more than 48%. On the field, we
can get an estimate visually, which is semi-quantitative
determination and is used as the following scale: 0%- 5%very bad
porosity (can be ignored)5%- 10%bad porosity 10%- 15%sufficent
porosity 15%- 20%well porosity > 25% excellent porosity
2.2. Saturation Reservoir fluid saturation is defined as the
ratio between the volume of a particular fluid (water, oil, or gas)
to total pore volume. Generally, the formation of the water content
in the oil zone is called interstitial formation water or connate
water. Water saturation is defined as:
...(4)
Oil saturation is defined as: ......................(5)
Gas saturation is defined as:
...........(6)
Sw + So + Sg = 1 .................(7)
2.3. PermeabilityBasis for determining the permeability of the
rock is from trials conducted by Darcy. In the experiments, Henry
Darcy using sandstone that is not compact by flowing water. The
porous sandstone saturated with 100% fluid viscosity,
cross-sectional area A, length L. Then, by applying pressure P1
entrance at one end, then the flow occurs at a rate of q, while the
external pressure P2. In this experiment it can be shown that q is
constant and will be equal to the price of the rock permeability is
independent of the fluid, the pressure difference and the
dimensions of the rock used. Because Henry is considered a pioneer
darcy permeabilitys investigation then is Darcy permeability for
the unit. Permeability itself is divided into two, namely: 1.
Absolut Permeability is the permeability where fluid flow in porous
media consists of only one phase, ex: only gas, oil, or water. 2.
Effective Permeability is a permeability where fluid is flowing
through a porous medium is more than one phase, ex: oil and water,
oil and gas, water and gas, or all three. 3. Relative Permeability
is the ratio between the effective permeability to absolute
permeability.
Definition API to 1 Darcy is a porous medium having a
permeability of 1 Darcy if single phase fluid with viscosity 1 cp,
flowing with a speed of 1 cm / sec, through the cross-sectional
area of 1 cm at a hydraulic gradient of 1 atm (76.00 mmHg) per cm
and the liquid fills the medium. Mathematically it can be written
as follows: ................. (8)Wherein:K = permeability, Darcyq =
flow rate, cc/sec = Viscosity, cpA = cross-sectional area, cmL =
length, cmP1P2 = pressure difference, atm
In Darcy's law itself there are assumptions that are used, as
follows: a) linear flow. b) in compressible fluid (can not breath /
full because if crowded / full it does not cause the volume
decreases. c) steady flow conditions (no change in the P and T). d)
homogeneous and isotropic porous media. In units of the field K is
expressed in miliDarcy. In the field estimate can also be made
semi-cumulative giving to the permeability (K scale), they
are:1.Tight: < 5 md2.Fair: 5 10 md3.Good: 10 100 md4.Very good :
100 1000 md
2.4. Acid solutibilityAcidizing is the way to stimulate the
reservoir consisting of limestone or dolomite reservoir rocks and
acid dissolvable rock. This is done by injecting acid into the
reservoir to get the price of the permeability and porosity of the
larger or more commercial in an oil field. The acid used is 15% of
the acid chloride reacts with carbonate rocks according to the
equation:
CaCO3 + 2 HCl CaCl2 + H2O + CO2Prior to stimulation with
acidizing must be planned precisely laboratory data obtained from
samples of formation fluid and the fluid reservoir stimulation so
that the information obtained from the laboratory can be used to
plan operations with proper stimulation. And, in turn, increase the
productivity of the formation can be obtained as expected. One of
the required information is the solubility of the acid rock samples
(acid solubility). This method uses a gravimetric technique for
determining the reactivity of the acid formation. Acidification
method (Acidizing) can be divided into two kinds:
1. Matrix Acidizing, in this method, the acidic solution is
pumped or injected in order to dissolve the rock and sediment
formations around the wellbore. The pressure used is smaller than
the fracturing pressure of the formation. Thus, the acid can react
with the walls of the pores of the rock and eventually will enlarge
pores. The maximum radial penetration and acid solution is
dependent on the speed of the acid in the pores. Some of the
assumptions used in the implementation of this method are as
follows: a. Homogeneous formationb. Uniform pore size c.
Penetration of acid solution uniformly and radially d. Reaction
speed decreases uniformly with decreasing acid concentration e. The
weight of limestone is dissolved on any additional distance
decreases uniformly until all the acid used. Based on the above
assumptions, the radial distance of the acid solution will
penetrate the formation before the acid solution used up entirely,
can be formulated by the following equation:
Injected acid volume = volume of pores invaded :
qi . t = . h . (ra2 rw2)...........(9)
ra = + rw2 .....(10)If qi is expressed in barrels / min and t in
seconds, then the equation can:ra = + rw2...(11)
where: ra = radial distance of acid penetration, ft. = porosity,
fraction. qi = acid injection rate, bbl / min. rw = radius of
wellbore, ft. h = thickness of the formation.
In the above equation, the unknown factor is spending time,
which must be specified in laboratory.spending time depends on the
ratio of the rock with an acid solution, which is called the
surface area.For specific matrix acidizing the area are:S f = 102 x
102..(12)
where: K = permeability (darcy) Sf = specific surface (cm2 /
cm3) F = factor formation custody
To get the fluid penetration and good acid, necessary reduction
reaction rate and raise the rate of injection of acid solution into
the formation. Spending time acid depends also on the pressure,
temperature, speed and acid in retarding from the additives of the
rock.
3. EXPERIMENT PROCEDURE3.1. Porosity Porosity measurements by
weighing method. Started by weighing the dry cores in a bowl, for
example, the dry core weight = W1 grams. The second take a core
that has been saturated in kerosene kerosene then weigh them, eg
severity = W2 grams. Taking the third core (which is still
saturated with kerosene), then weighed in air, such as severity =
W3 grams. The latter calculate Vb, Vg, Vp.
3.2. SaturationSaturation measurements by the method of
distillation. First of all take a fresh core or that has been
saturated with water and oil. The second considers the core, for
example weighs a gram. The third insert the core into the Dean
& Stark flask filled with toluene. Then we fill with water trap
and a reflux condenser. The fourth heat for approximately 30
minutes until the water is no longer visible. Cool it and read the
fifth volume of water being stored in the water trap, the trap eg
cc = b = b g. Drying sixth sample in the oven for 15 minutes, then
cool it in exicator. Then weigh the dry cores, eg = c g. The
seventh Then we can calculate the weight of the oil to the equation
"a - (b + c) g = d g". Next calculate the volume of oil. And lastly
calculate oil saturation and water saturation.
3.3. PermeabilityTo measure liquid permeability, using a liquid
permeameter. First insert the core into the core holder. The second
filling burette with water (test liquid). The third open valve core
holder and burette filled. The fourth shut off valve. The fifth set
the desired pressure on the pressure gauge to set the pressure
regulator. Next restore the fill valve discharge to discharge. The
latter recorded the time required to drain fluid from the upper
limit to the lower limit burette, and calculate permeability. To
calculate the gas permeability, we use gas permeameter. First of
all make sure regulating valve closed, connect the gas line to the
gas entering inlet. Both cores on the core holder. The third play
flowmeter selector valve on the "large". The fourth open the
regulating valve, rotate until the pressure gauge shows the number
of 0.25 atm. The fifth pick in the reader flowmeter range between
20-140 division. Next if under 20, turn the selector valve to the
"medium" and raise the pressure to 0.5 atm. If the reader on the
flowmeter under 20, turning the selector valve to the "small" and
raise the pressure to 1.0 atm. If the flowmeter remains up from
number 20, stop the experiment and check cores in core holder. If
the flowmeter shows a number above 140 in the "large" cane, the
permeability of the core is too large. Experiments we stop or try
raising long cores or reducing the cross sectional area of the
core. Then record the temperature, pressure and flowmeter readings.
Do not forget to change the pressure to 0.25 atm with regulators.
The latter experiment repeated 3 times.
3.4. Determination of formation samples dissolved in acid
solutionThe first thing to do is prepare the carbonate rock samples
that have been dried and weighed.The second is to prepare a
solution of 5N HCl acid for the carbonate rocks. The third, insert
the carbonate rocks into HCl solution for 10 minutes. Next , insert
the stone into the oven for 20 minutes to dry. And than, weigh the
carbonat rock. Calculated the solubility as weight% and the
solubility of the material dissolved in 5N HCl
4. DISCUSSIONPorosity measurements or samples of reservoir rocks
is to know the size of the cavity in the rock by rock bulk volume
and pore volume of the rock. In the process of exploitation, rock
porosity criteria that will be produced is effective porosity rocks
or in other words the ratio of the pore volume that related to the
total volume of rock. In this experiment a reservoir rock porosity
measurements, carried out in two ways: with mercury injection and
by weighing. But we only use the weighing method only, due to
damage of mercury injection apparatus. Where in this experiment the
number of porosity obtained from experiments with the weighing
method obtained at 18.375% effective porosity, thus belonging to
the good porosity.Measurement of Fluid Saturation its purpose to
determine the pore space of reservoir rocks containing fluid
especially oil. The pores of the reservoir rock containing fluid
usually consists of oil, water and gas. This is related to the
estimated size of the reserve reservoir. In this experiment, fluid
saturation measurements performed by the method of distillation.
From the experiment, obtained oil saturation (So) of 0.8824, water
saturation (Sw) of 0.1176, and gas saturation (Sg) of 0. This
indicates that the core sample saturated by two kinds of fluids,
oil and water. Where there is no gas saturation, so that the gas
saturation is 0.Permeability measurements are used to determine the
ability of a fluid reservoir rocks passed without damaging the
structure of the constituent rocks. With permeability measurements
we can determine the fluid flow rate. In experiments using the
absolute permeability permeameter measurements were performed with
two methods: liquid permeameter and gas permeameter which each
method performed 3 times in order to get the price of permeability
K1, K2 and K3. Getting a number of permeability with Liquid
permeameter method as follows K = 0.0236 darcy. Whereas the gas
permeameter method obtained price = 0.01235 darcy permeability K1,
K2 and K3 = 0.01395 = 0.0125 darcy darcy. Where K is the value of K
that has not been corrected by the effect Klikenberg. When the
amount of permeability is inserted into the table K vs. 1 / P then
expressed in the graph. From the graph obtained linear equation y =
0,0004x + 0.0126. The equation used to find the factors Klikenberg
permeability (K *). K * generated at 0.1329.
Determination of formation samples dissolved in acid solution,
determine the levels of soluble formation in acid solution, in
order to obtain important information prior to stimulation. In this
experiment the aim to clean up or dissolve impurities reservoir
rocks with an acid solution, can also increase the average rate of
production. Acidification is done in this experiment using 5 N HCL
with concretration due to the nature of HCL that reacted with
carbonate. From this experiment price percent solubility obtained
was 15.78% or mean pore blockage in the core of 15.7% acid.
5. CONCLUTION
Of all the experiments that have been carried out in general it
can be concluded that:
1. Analysis of the core is an attempt to get information about
the physical properties of rocks. In its application is very useful
for a lot of help in the withdrawal of oil and gas, particularly in
deciding how best to do the production.
2. Porosity shows the amount of pores in the rock cavities that
can be occupied by the fluid. The surface obtained is effective
porosity. In experiments obtained 18.375% porosity sandstone with
the weighing method. Some factors affecting the porosity is:
quantity or temperature which is composed of rock, grain
uniformity, shape and structure of the rock, cementation,
compaction, angularity, packing, fracture due to secondary
processes.
3. Definition of fluid saturation, fluid saturation is the ratio
of the pore volume occupied by a particular fluid with the rock
pore volume. Saturation is composed of water saturation (Sw), oil
saturation (So), gas saturation (Sg). From the obtained trial So =
0.1176; Sw = 0.8824; Sg = 0.
4. The larger permeability of the reservoir rock, the less time
needed to fluid through the pores rock which are interconnected, so
that the production rate will be expand. In the experiment get
permeability (K) in the gas permeameter tool that is: P = 0.25 atm
to K = 0.01235; P = 0.5 atm K = 0.01395 Darcy,; P = 1 atm K =
0.0125 Darcy. In liquid permeameter, P = 1 atm obtained K = 0.0236
Darcy. Permeability is closely related to the porosity, so it can
be concluded that permeable rock shaft but not necessarily always
the opposite. Several factors influence permeability
5. The solubility degree of the sample in acid solution is
15,78%. So, if we do the acidizing using HCl, most of the
depositions will be soluble in acid solution. It is proper to do
the acidizing using HCl.storage by reinjection into reservoir
formations. Above measuring petrophysics, we can indicates that
limestone which we take is bad to be a reservoir rock
6. The rock samples have high porosity values and permeability
values are low because of the rock sample is included in the
classification of clastic limestone carbonates where porosity is
usually obtained intergranuler porosity type, which is sometimes
also enlarged by the dissolution. Porosity can reach as high as
18,375 %, but only has K = 0.0236 darcy permeability.
Reference1. Buku Petunjuk Praktikum Analisa Inti Batuan,
Laboratorium Fakultas Teknologi Mineral, Jurusan Teknik
Perminyakan, Universitas Pembangunan Nasional Veteran
Yogyakarta.2013.2. Tiab , Djebbar and Donaldson Erle C.
Petrophysics : theory and practice of measuring reservoir rock and
fluid transport properties. United States of America, 2004.
Appendix
Rocks in the field (Kemadang area) and core samples
Korea National Oil Team in Kemadang area
Kemadang Village Map
Laboratory tools
Porosimeter, analog scale, and digital scale
Dean & Stark aparatus, gas permeameter, liquid permeameter,
and oven.
Graphic 1/P vs K