Oil and Gas Production Surveillance Techniques

PRODUCTION SURVEILLANCE TECHNIQUES

Cedric KimloazID#: 107000908

INTRODUCTION Production Surveillance refers to the procedure of

measuring and monitoring fluid properties over the life of the well.

This can be useful for: Identifying production and mechanical problems Generating flow profiles to determine gas, oil, and

water holdup Monitoring changes in fluid saturation during

production Comparison with expected well performance

Ultimate purpose is to provide info. which can help to maximize oil recovery, extend life of well, reduce operating cost.

SCOPE AND OBJECTIVES Mention of science, logging procedure,

interpretation, applications, and tools used to measure the following fluid properties: Pressure Temperature Fluid density Fluid velocity Photoelectric Absorption Capacity Radioactivity Sound Transmission Characteristics Dielectric constant

SCOPE AND OBJECTIVES Gas and Oil Well Deliverability Testing

Productivity Indicator (AOFP) Inflow Performance Relationship (IPR)

Prediction of future production at any stage in the reservoir life

Influence of changes in drawdown, tubing size, and stimulation on production.

Productivity Index test for oil wells (simplest form of deliverability test)

Transient pressure analysis - not considered a Production Surveillance technique, but can help in well problem diagnosis.

SCOPE AND OBJECTIVES

Fluid Sampling TechniquesDrill Stem Testing – determines the

potential of the formation. Involves simultaneously recording formation pressure while taking fluid samples.

Repeat or Wireline Formation Tester – confirms the presence of formation fluid, while giving an indication of productivity and formation pressure.

PRODUCTION LOGGING TOOLS Can be run in cased-hole production or

injection wells – Cased hole Production Logging.

In wells with tubing, the tool may be run through the tubing – Through-Tubing Production Logging.

Tool can be run on electric wireline and records taken at surface, or on a slick wireline and records taken on BH charts or magnetic tape.

A lubricator is installed on the WH Will only function properly at a maximum

Ph of 15,000 psi and max wellbore temp. of 350°F

PRODUCTION PROBLEMS Production Log data can be interpreted to help identify some

of the following: Mechanical condition of the well

Csg, tubing, and packer leaks Wellbore restrictions Corrosion damage

Anomalous Fluid Movements Between Zones Channel due to poor primary cement job. Flow into thief zones

Evaluation of Completion Efficiency (Producing Well) Negligible or no contribution from some zones Zones contributing only water or gas, when oil is expected Zones producing below forecasted potential Location of points of fluid entry

PRODUCTION PROBLEMS Evaluation of Completion Efficiency (Injection

Well) Indentify zones to which the injected fluid is

enteringQuantifying of injected fluid entering zone(s)

Design and Evaluation of Stimulation Treatment Indentify zones requiring stimulationZones to which stimulation fluid is enteringMonitor reservoir performance after stimulation

Reservoir Management Initial fluid saturations in each zoneSaturation changes due to production or fluid

movement

TYPICAL BREAKDOWN OF SOME RANDOM PL OPERATIONS BY REASON FOR JOB

BH PRESSURE GAUGES

Quartz Pressure Single (QPS) Gauge is the typical tool used.

Measurements can be made at one depth (Pwf) or several depths with the well flowing. Pressure change with depth (pressure gradient) indicates fluid density.

Measurements can also be made with the well shut in (Pws).

The measurement is made at the midpoint of the perforations (MMP).

THEORY OF OPERATION OF THE QPS

Bellows

•Receives hydrostatic pressure

•Transmits to QPC via piston-like displacement of silicone oil

Quartz Pressu

re Crysta

l

•Oscillates at its natural frequency, which changes proportionally Ph.

Reference

Temperature Crysta

l

•Not exposed to well pressure.

•Measures the temp. of the pressure crystal and reduces output frequency.

SPINNER FLOWMETER LOGGING

Measures well fluid velocity using a turbine impeller.

There are different variations of the tool for different logging and wellbore conditions.

Rate at which spinner rotates is proportional to fluid velocity, and a flow log of velocity vs. depth is produced.

The main reasons for measuring flowrate downhole :To determine which intervals are

producing.How much they are producing?To locate any possible thief zones

SPINNER FLOWMETER LOGGING Can be run in a static mode for stationary readings,

or in a dynamic mode for a profile of flow. Dynamic operation offers the following advantages

over static operation: Covers more of the well ,shows precise location of flow

entry or exit. Data is collected faster. Flow test resolution is increased. They are less prone to depth errors.

Static spinner tests are easier to quantify since correction for logging speed is not required.

Ideal practice - profile the well in dynamic mode, and collect stationary readings at selected zones e.g. perforation depths.

TYPES OF SPINNER FLOWMETERS

1500bpd in 7” csg

No upper limit on flow velocity

Min 65bpd in 51/2” csg

Upper limit of 400 bpd in 51/2” csg

TYPICAL SPINNER FLOWMETER

TEMPERATURE LOG High Resolution Thermometer A platinum resistor sensor (temperature sensitive)

is enclosed in an probe tube exposed to the wellbore fluid.

Resistance of the sensor is affected by temperature changes which causes a differential voltage across the probe.

Differential voltage converted to a frequency and output as a temperature measurement.

The measurement is then amplified electronically to give very high resolution.

SCHEMATIC OF THE HIGH RESOLUTION THERMOMETER

APPLICATIONS OF THE TEMP. LOG Identification of points of gas entry, or gas

channelling – gas expansion results in significant cooling.

Identification of points of liquid entry – liquid expansion results in a slight heating effect.

Static fluid temp is primarily affected by conduction. Hence if the geothermal grad. is known, the temperatures displayed on the log can be compared to calculated temps to distinguish between gas or liquid flow.

FACTORS AFFECTING GEOTHERMAL GRADIENT

Geothermal gradient in a particular area is dependent on the conductivity of the formations.varies with lithologygeological features e.g. washouts

The greater mass of cement required to fill a washout provides insulation which tends to mask the temp readings.

Therefore the geology and borehole rogusity must be known.

NOISE/ACOUSTIC LOG A noise log is a recording of the amplitude of

audible sound frequencies generated by moving liquid or gas at various points in the well

The sounds/noises can be attributed to pressure drops as fluids enter the wellbore.

Can be used to determine: The presence of flow. The path of the flow. Fluid phases involved.

High-noise amplitudes indicate locations of greater turbulence e.g. leaks, channels, and perforations

NOISE/ACOUSTIC LOG

The noise tool is usually run in conjunction with the temperature tool, and they are the best tools for locating and defining flow behind casing.

Cooling areas are indentified on the temperature log, and the noise log is then used to analyze these cooling zones for indications of gas entry, or gas channelling.

TOOL DESCRIPTION

Tool is about 1.5” in diameter and 6’ in length.

The microphone detects the sound which is amplified and sent to surface for filtering.

At surface the noise amplitude spectrum is filtered .

A plot of amplitude versus frequency is then generated on an oscilloscope.

TYPICAL NOISE SPECTRUM Frequency ranges are

compared with known sound patterns developed in lab simulations.

At ∆P>100psi, most of the sonic energy above 100 Hz is created by gas movement.

Single phase liquid movement creates more energy below 1000 Hz

Two phase flow usually creates a peak in the 200-600 Hz band

GRADIOMANOMETER

Records the ∆P between two sensing bellows spaced 2 ft apart.

∆P = hydrostatic head + friction head + kinetic head.

However, for laminar steady state flow, friction and kinetic effects are negligible

Under these conditions ∆P = ρg(h2-h1)

APPLICATIONS OF THE GRADIOMANOMETER

Most effective for identifying gas entry and locating standing water levels

Water holdup can be calculated at various levels in the wellbore,

ρt determined from dynamic gradiomanometer measurements at various levels.

Slip velocity can be determined using an empirical chart, once ρw – ρo, and yw are known.

The oil and water velocity can then be determined using

EMPIRICAL CHART FOR DETERMINING VS

PULSE NEUTRON CAPTURE LOGGING

ApplicationsPorosity EvaluationSw at different stages of productionDetection of gas bearing zones

Formation water salinity must be at least

50,000 ppm and ø > 15%

OPERATING PRINCIPLE

Small-diameter through-tubing tool less than 2”.

Electronically activated neutron generator, and two detectors (sodium iodide scintillation).

The detectors cannot distinguish sources of 𝜰energy. As such the tool measures background count rate.

It is essentially a TDT device -measures the time taken for neutron population to decrease to 65% of No.

NEUTRON CAPTURE THEORY

Tool emits a burst of high

energy neutrons

Lose energy quickly slowing down to thermal

state

Thermal neutrons

captured by the formation

and fluid in pore spaces

Gamma ray released

Detected by tool

•The measure of the atom’s ability to capture these neutrons is called the capture cross section (𝜮) = 4550/𝝉•The count rate of the gamma rays indicate the rate of neutron population decay. 𝜰count rate and rate of neutron decay yield a measurement of neutron CCS of the formation.•The neutron population decays exponentially according to the equation,

EVALUATION OF WATER SATURATION (SW) BEHIND CASING

• Porosity can be obtained from

the corrected øN, øD logs, or sonic log.

• Shale content can be obtained from the gamma ray log and a simple calculation.

FACTORS AFFECTING INTERPRETATION

Invasion – The TDT device has a relatively shallow depth of investigation. Fluids in the invaded zone would influence the CCS measurement, which would increase or decrease Sw depending on the type of the mud filtrate.

Lithology - Rock salt or other minerals with a high capture cross-section will cause high values, and 𝜮therefore high Sw.

OXYGEN-ACTIVATION

Detects water movement past the logging tool.

When the neutron burst occurs, O2 present in theH2O molecules becomes activated to an unstable isotope with a half-life of about 7 s. As isotope returns to its normal state, gamma rays are emitted which are detected by the near and far background count rate measurement.

INTERPRETATION OF COMPOSITE PRODUCTION LOGS

At top of well there is a drastic reduction in fluid density which is confirmed as pt. of gas entry into the wellbore.

There is also a reduction in temp. at the top which is caused by gas expansion.

The capacitance increased significantly at the bottom, which corresponding to a fluid type with a very high dielectric constant (80).

The flowmeter speed also increased at the bottom corresponding to oil and water flow.

GAS WELL DELIVERABILITY TESTING

Determination of productivity indicator, AOFP. Maximum rate at which a well can flow against a theoretical atm. Backpressure at the sandface. Used by regulatory bodies to limit production rate.

IPR – relationship between surface production rate and Pwf.

The three most common types of gas well deliverability tests are: Flow-after-flow or Conventional backpressure test Isochronal test Modified isochronal test

FLOW-AFTER-FLOW TEST

Each flowrate is established in succession without an immediate shut-in period.

ISOCHRONAL TEST

The well is not allowed to flow for long periods to achieve stabilized flow conditions.

MODIFIED ISOCHRONAL TEST

Pws is not allowed to build up to the stabilized shut in pressure after each flow period.

ANALYSIS OF CONVENTIONAL BACKPRESSURE TESTS

OIL WELL DELIVERABILITY TESTING

Oil well deliverability testing allows us to determine IPR which is used to: Forecast production at any stage in the life of the

well. Determine how production will change for a

particular drawdown. Determine qomax or absolute open-flow potential. Monitor how production changes with tubing

sizes. Monitor production changes after stimulation.

PRODUCTIVITY INDEX (PI) TEST

Involves the measurement of Pws , and at one stabilized producing condition, measurement of Pwf and corresponding surface flowrates.

This is a measure of the ability of a well to produce.

PI declines during the life of the well due to many factors e.g. flow restrictions and near wellbore damage. Hence its a useful indicator of wellbore conditions.

FOR UNDER-SATURATED OIL WELLS

For production where Pr >Pb, PI may be constant over a wide range of pressure DD.However when Pr<Pb, and gas now occupying a portion of the pore spaces, PI decreases with increased DD.

SATURATED OIL WELLS

DRILL STEM TESTING

Done on newly drilled exploratory wells.

Determines the potential of a producing formation, and involves simultaneously recording the formation pressure while taking samples of pristine formation fluid.

BHA – 2 isolating packers, surface operated DST valve

 REPEAT FORMATION TESTER (RFT)

Confirmation of formation fluid, indications of productivity, and formation pressure

Tool consists of – a packer, hydraulic piston, two sample chambers (2 ¾” gal), pre-test chambers (indicates whether or not a packer seal is obtained).

The piston creates the DD, while the 2 fluid samples are obtained simultaneously from prospective zones.