Formation Evaluation.ppt

5/22/2018 Formation Evaluation.ppt

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PETROLEUM ENGINEERING PETROLEUM GEOSCIENCE ENGINEERING

PEEG 151

PEEG151

Chapter 7:

Formation Evaluation

Material prepared by:

Dr. Karl Berteussen

Dr. John Williams

Richard Lau


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Chapter 7 - Formation Evaluation

Data Requirements

Rock/formation properties

Fluid properties

(hydrocarbon and water) Flow potential

There was

no oil here

when we

drilled!

Why Must We Evaluate the

Formation?

At least;

study the

cuttings.


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Chapter 7 - Formation Evaluation

Why Must We Evaluate the Formation? Data Requirements Rock/formation properties (thickness, lithology, porosity,

permeability, pressure)

Fluid properties (hydrocarbon and water, saturation)

Flow potential

Data While Drilling Drilling Operations Log (progress, mud, cuttings, etc.)

Cores

Flow Potential (Drill Stem Test)

(and today we have MWD or LWD or Wireline Formation Test)

After Drilling Open-Hole Well Logs (before casing!)

Cased-Hole Logs (CBL)

Initial Production

Reservoir Fluid Samples

Sometimes wells

are drilled only

to gatherinformation.


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Drilling Operations Log

Wellsite

geologist

Continuous record of the hole as it is being drilled;

cuttings, mud returns, drilling operations plotted against depth

Cuttings data:Lithology (correlation)

PorosityOil Shows

Gas Shows

Hydrocarbon Odor

Cuttings data Problem:Lag time

Disintegrated

Re drilled


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MUD DATA

Continuous monitoring

Gas shows

Oil shows


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Cores Provide Valuable Data

Core analysisPorosity (several methods)

Fluid saturations

Permeability

Vertical

Horizontal

Some fluid data

(often contaminated)

Conventional CORING

Diamond

or PDC bit


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Sidewall CoreGun:Typical sample 2

inch long half inch

diameter

Sidewall CORINGRun on wireline

Usually in soft unconsolidated

formation.

Cylinder impact might crush

core, i.e. porosity & permeability

might not be correct


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Productivity or Production Tests

(Important Information!) Potential flow rates,

Permeability,

Fluid properties, and in some cases

Reservoir boundaries.

Better Method than the alternatives

(Well logs give only indirect indications of

permeability and fluid saturations)Costly development mistakes have been made

using inadequate or no production tests

SPE definition of reserves as proved requires

confirmation through production testing


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Production Tests

1. Drillstem testing (DST)

2. Wireline formation testing (WFT)

Drillstem testing (DST)

Tool run on drillstring Fluid flow & pressure versus

time.

Good productivity data, fluidsamples

Indication of reservoir boundary(size)

Expensive, high risk of packerfailure


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12345

1. Both valves closed(Does not feel outside

pressure, ref figure.)

2. Open bottom valve

3. Open top valve4. Close top valve

5. Close bottom valve


hourorso

H

ighDrama

W

ant:Oiltosurface

Afterwards: String pulled wet --- meaning what?

Information stored in downhole sensors, brought up.Can get info immediately, how?


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Production Tests


Wireline formation testing (WFT)

smaller tool,

smaller test,

less fluid,

results less reliable

Can test multiple zones



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Wireline Formation Testing

Springforce

Electric conductingwireline

Test

tool

Formation pressureFlow samples



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Initial Potential (IP) test(discussed in detailchapter 9)

Well completed and load fluids removed

Typically 24 hours

Reports Produced barrels of Oil

Produced barrels of Water

Produced MCF of Gas

Tubing pressure Choke size

Marks the wells transition from drilling toproduction or other status

If artificial lift:

Parameters are described



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Production Testing Challenges

May be difficult to get the packer to seal(especially when dual-packers are used)

DSTs can also be run after wells have beencompleted, cased and perforated.

Wireline formation testing data are of less quality(small volumes of fluid involved)

WFT samples are usually contaminated to some

degree Gas reservoir productivity requires extended

production testing

Wireline results can be used to determine where

DSTs need to be run.



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Open-Hole Well Logs

Operations:

Sonde lowered to the bottom then

slowly retrieved as logging takes place.

Often several different measurements

are made in one run.



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Logging Tools

Spontaneous Potential (SP) - Lithology

Gamma rayLithology

Sonic or Acoustic

Porosity DensityPorosity

NeutronPorosity

Resistivity

Formation Fluids

CaliperHole diameter & Permeability



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Spontaneous Potential (SP)

Spontaneous Potential (SP):

Measures electrochemical

potential present in the

borehole at boundaries

between porous, permeable

zones and surroundingshales:

Lithology indicatorDepth

The potential difference (DC voltage)

between a movable electrode in the

borehole and a distant reference electrode

usually at surface. The voltage is due to

currents generated by the Electrochemicaland Electrokinetic potentials



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Gamma Ray Log

A common and inexpensive measurement

of the natural emission of gamma rays by a

formation. Gamma ray logs are particularly helpful

because shales and sandstones typically

have different gamma ray signatures thatcan be correlated readily between wells.

(shales emit more gamma rays)



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More logs

Density Logs (Gamma)

Emits gamma rays

Returned radiation (gamma source),

more absorbed implies greater density.

Neutron logs

Emits neutrons

Hydrogen (in water and oil) will capture them Returned neutron gives porosity

(gas exception, used to differentiate gas and oil (togetherwith density log))



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Resistivity Logs

Saltwater saturatedporous zones

conduct electrical

current better than

same zones with oil,

natural gas or freshwater.

Resistivity ~ potential/current

Resistivity

SP

More porous/

permeable

Note: This figure isa graphit does not

show the actual hole

dimension.

WellDepth



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Spontaneous Potential

(SP) - Lithology

Gamma ray

Lithology

Resistivity

Formation Fluids

Neutron

Porosity DensityPorosity

(emits gamma rays)

Sonic or Acoustic

Porosity

Caliper

Hole

Diameter &

Permeability

Log overview



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Reservoir Fluid Samples:

Hydrocarbons

Samples can be taken in the well (downhole or bottomhole sampling) or from surface production (well heador separator samples)

Fluid samples are used to perform Pressure-Volume-Temperature (PVT) studies which model reservoirdepletion and surface production processes

Samples are analysed to provide a detailed fluidcomposition, which is used as a basis for reservoirsimulation, facilities design, and determination of sales

values



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Reservoir Fluid Samples:

Formation Water Samples of reservoir water also give

valuable data

They can help in the interpretation of logs.

In many cases no formation water is

produced in a DST.



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Chapter 7

FINISHED

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