Formation Testng and Sampling

7/27/2019 Formation Testng and Sampling

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Wireline Logging

Formation Testing and Fluid

Sampling


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Overview

Formation: Reservoir quality Fluid: Oil, Gas or Water?

Borehole: Environmental factors


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Formation Properties

Radioactivity Porosity

Grain density Pore Size Stratigraphy

Bedding, Dip Sonic Velocity Seismic Velocity


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Fluid Properties

Salinity (Resistivity) Density

Saturation Pressure Temperature

Viscosity Mobility Bubble Point


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Borehole Properties

Depth Caliper

Spontaneous Potential Temperature Cable Tension Deviation, Azimuth


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History

First tools for sampling only (FIT) Next generation added pretest capability to

check permeability before committing tosampling (RFT)

Pressure tests became even more important thatsampling.

Latest tools are modular and permit manycombinations of probes, sensors and samplechambers (RDT, MDT).


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Tool Modules

Modern tools can be configured from a selectionof modules: Power Module (top of tool)

Hydraulic Module (top of hydraulic bus)

Probe /Dual Probe Module

Pump Out Module

Sample Chambers

Multisample (PVT) chamber carriers

Fluid Analyser modules (optical/NMR)

Inflate packer modules


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Example Configuration


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Probe Module (MDT)


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Gauge Types

Quartz Gauge Most accurate

Highest resolution

Slow temperature stabilisation Complex calibration

Measures absolute pressure (PsiA)

Strain Guage Lower accuracy

Fast response Easy calibration (dead weight tester)

Relative to atmospheric pressure (PsiG) = PsiA 14.7 psi


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RDT vs MDT

RDT has two probes on standard probemodule.

Each probe can be connected ordisconnected from the flowline. Each probe has its own Strain/Sapphire

gauge.

The Quartz gauge is in a separate moduleon the flowline.


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Pressure Testing Theory

We set the tool to lock it in position Next we extend a probe into the formation

sealed with a rubber packer

The formation fluid is sucked into the tool usinga pretest piston (0-100cc).

We then wait for the formation pressure to build

up to its true value. The speed of build up gives a measure offormation mobility (md/cp).


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Pretest Plot Features


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Pretest Types

If the pressure does not build up in a reasonabletime it is a dry test or tight test.

If the pressure returns to hydrostatic it is a sealfailure. If the formation pressure stabilises (slowly) to a

higher than normal value it is supercharged.

All other tests that yield a valid formationpressure are Normal Tests.


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Dry Test Example


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Seal Failure Example


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Pretest Applications

Pressure Gradients to determine fluidtype.

Looking for communication between wells. Checking for drawdown in producing

fields.

Estimating formation mobility /permeability.


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Pressure Gradients

Pressure must be plotted against depth TVD(not MD).

Mud gradient will depend on mud weight.

Fresh Water gradient will be approx 0.43 psi/ft Oil gradient 0.25-0.35 psi/ft Condensate gradient 0.15 0.2 psi/ft Gas gradient 0.01 0.1 psi/ft Density (g/cc) = Gradient (psi/ft) / 0.433 Density (lb/gal) = Gradient (psi/ft) * 19.27


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Gradient Errors

Gradient can be affected by errors inpressure and depth.

For example two water points 2 feet apartwill show 0.37 0.61 psi/ft for a totaldepth error of +/- 6

The same points will plot at 0.36 0.56psi/ft for a +/- 0.2 psi error in pressuredifference.


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Pressure Gradient Plot


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Real Pressure Data

y = 2.3131x - 61.504

R2

= 0.9956

y = 1.996x - 86.167

R2

= 0.9996

1500.0

1600.0

1700.0

1800.0

1900.0

2000.0

2100.0

2200.0

2300.0

2400.0

2500.0

2600.0

2700.0

2800.0

2900.0

3000.0

3100.0

3200.0

3300.0

3400.0

3500.0

700 800 900 1000 1100 1200 1300 1400 1500 1600 1700

Formation Pressure (PSIA)

TVDSS

(ft.)

Hydrostatic Pressure

Formation Pressure

Formation Gradient psi/ft

Hydrostatic Pressure


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Fluid Sampling


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Pumpout


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Bubble Point

The bubble point is the pressure belowwhich gas will start to come out of

solution. It is essential for good quality PVTsamples that the sample never passesthrough the bubble point.

This is accomplished by using low shockPVT sampling techniques.


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Low Shock Sampling

Following the pretest the formation fluid is pumped outto the borehole, maintaining pressure above bubblepoint.

Once the fluid contamination has dropped below anacceptable threshold the sample bottle is opened.

When the outlet port is closed the pressure increasesand the fluid is pumped into the bottle againsthydrostatic pressure.

When the bottle is full pressure rises again and thebottle is sealed at above hydrostatic pressure.

This is required so that at surface temperature thepressure will remain above the bubble point.


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Fluid Properties

All tools have a Resistivity sensor Resistivity should distinguish between

OBM filtrate and water (but not gas or oil). MDT has optional optical fluid detection

that can distinguish filtrate from oil/gasand detect CO2 (latest version LFA)

RDT has optional NMR module that canclearly differentiate oil and OBM filtrate.


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Formation Testing Test 1

1. Name the two modules that cannot beanywhere in the tool string but must be at thetop.

2. Of the two which must be above the other?3. Which gauge type has the highest accuracy

Quartz or Strain?

4. Which has the fastest response?5. What is the expected pressure differencebetween them?


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6. What are the primary uses for formationpressure measurements (pretests)?

7. What do we call a pretest that fails to build up?8. What do we call a pretest that builds up tohydrostatic pressure?

9. What do we call a pretest that slowly builds toan abnormally high pressure?

10.What are all other pretests called?


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11.What is a fresh water gradient?12.What is a typical gas gradient?

13.Why do we calculate gradients usingTVD depths?

14.How do we reduce contamination ofsamples from mud filtrate?

15.What is the point of low shocksampling?


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16.What is the bubble point?17.Describe how low shock sampling is

performed.

18.Why do we overpressure the sample beforesealing the bottle?

19.What fluid properties can we measure in the

standard tools?20.What additional fluid identification modules areavailable?

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Formation Testng and Sampling