H (I-4) Oil Displacement Concepts

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Basics of Reservoir Engineering – Module I

I.4 – Oil Displacement Concepts




Primary Recovery

Hydrocarbon production resulting from natural reservoirenergy

Natural reservoir energy sources

• Rock and fluid expansion

• Solution gas drive

• Gravity drainage

• Water influx




Conventional Improved Recovery (IOR)

Injection of immiscible fluid

• Water injection

• Nitrogen injection

• Casinghead gas reinjection

Often used in ‘secondary recovery’


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Enhanced Oil Recovery (EOR)

Using chemical, biological, or thermal action to improve oil

recovery• Steam, CO2, or hydrocarbon gas injection

• Polymer and/or micellar injection• Microbe solution injection

Usually used in ‘tertiary recovery’



Waterflooding

Injection of water into a reservoir

• Increases reservoir energy

• Sweeps oil towards producing wells

Most widely applied secondary recovery method

Accounts for about 50% of U.S. oil production



History of Waterflooding

1865

~~

1920 1930 1940 1950 1960 1970 1980 1990

Waterflood projects in Oklahoma and Texas

Widescale waterflood

implementation

Infill drilling

Tertiaryrecovery

* First recorded waterflood



Goal of Waterflooding

Increase the amount of oil recovered from the reservoir by

• Maintaining reservoir pressure

• Displacing (sweeping) oil with water



Pressure Maintenance

Water treatment

plant

Water

injection

OWC

Sealing

fault

Gas

OilProduction

well



Gas Phase Effects

Reduction in reservoir pressure can cause

• Gas-cap expansion

• Secondary gas cap creation

• Gas saturation creation in pore spaces

Water injection can prevent or reverse these effects



Reservoir Performance

G

a s / o i l r a t i o

P r e s s u r e

Cumulative oil production

GOR

Too depleted for

WF success

pi

pb

Rsi

Pressure Gas

saturation G a s s a t u r a t i o n

P i D i M h i



Primary Drive Mechanisms

Most applicable:

• Solution-gas drive• Gas-cap drive

• Weak water drive

• Gravity drainage

Not applicable

• Strong water drive

E l 1



Example 1

Rate as good or fair or poor reservoirs as to theapplicability of waterflooding

E l 1 S l ti




Example 1 Solution

1. Fair 2. Fair

3. Poor 4. Good

5. Poor

6. Good7. Fair

W t I j ti T S Oil




Water Injection To Sweep Oil

Five - spot

Production well

Injection wellFuture inj. well

P i h l Fl di




Peripheral Flooding

Injectors

Producers

Line Drive Patterns




Line Drive Patterns

Direct Drive Staggered Drive

Injection

Well

ProductionWell

No-flow

Boundary

5 Spot Pattern




5-Spot Pattern

Injection well

Production

well

No-flow

boundary

7 Spot Pattern




7-Spot Pattern

InvertedNormal

InjectionWell

Production

Well

No-flow

Boundary

9 Spot Pattern




9-Spot Pattern

Normal

Nine - Spot

Inverted

Nine - Spot

Injection

Well

Production

Well

No-flow

Boundary

T i l I iti l Oil Fi ld D l t




Typical Initial Oil Field Development

1 Mile

1 Mile

Producing well

Dry hole

Typical Peripheral Waterflood Development




Typical Peripheral Waterflood Development

Producing well

Injection well

Dry hole

Typical Center-Line Injection Waterflood




Typical Center-Line Injection Waterflood

Development

Producing well

Injection well

Dry hole

Typical 160-Acre Inverted 9-Spot Waterflood




Typical 160-Acre Inverted 9-Spot Waterflood

Development

Producing well

Injection well

Dry hole

Typical 80-Acre 5-Spot Development




Typical 80 Acre 5 Spot Development

Existing injection

well

New conversionto injection

Producing wellDry hole



Typical Infill Drilled 40-Acre Direct




Typical Infill Drilled 40 Acre Direct

Line Drive Development

Existinginjection well

New conversion

to injection

New infill

producing well

Dry hole

Existingproducing well

Factors in Pattern Selection




Factors in Pattern Selection

Current well locations

Fracture azimuthsPermeability anisotropy

Field geometry

Injectivity

Infill drilling plans

Casing integrity of conversion injection candidates Adjacent lease considerations

Pattern Orientation




Pattern Orientation

Unfavorable

orientation

Favorable

orientation

Permeability

or

fracture

orientation

Pattern Selection/Orientation Problem




Pattern Selection/Orientation Problem

NNENW

W E

SESWS

Existingproducer

Existing

injector

New

producer

New

injector

Convert to

injector

Solution - Pattern Selection/Orientation Problem




NNENW

W E

SESWS

Existingproducer

Existing

injector

New

producer

New

injector Convert to

injector

Frontal Advance Theory




y

Water Oil

Swi

Sor

• Piston - like displacement

Connate water





y

Water

S a t u r a t i o n

Distance

Connate water

Initial oilsaturationInjected

water

bank

Oil

• ‘Leaky piston’





y

S a t u r a t i o n

Distance

Water bank Oilbank Unaffectedreservoir

Water Oil

Trapped gas

Initial

free gas

Connate water

Fractional Flow Equation




q

w

o

o

w

c

o

o

t

w

k k

L

P k

q

A x

f

µ µ

α γ µ

+

∆−∂∂+

=

−

1

sin433.010127.1

13





( )

w

o

o

w

c

o

o

wo

w

k k

L

P k

qq

A x

f

µ µ

α γ µ

+

∆−∂∂

++

=

−

1

sin433.010127.113





( ) L

P k

qq

A x c

o

o

wo ∂∂

+

−

µ

310127.1Capillary pressure term

(usually ignored)

Gravity term( ) ( )α γ

µ sin433.010127.1

3

∆+

−

o

o

rwro

k qq

A x





Horizontal reservoir

rw

ro

o

ww

k

k f

µ

µ += 1

1

Fractional Flow of Water is Affected by:




Increased Valueof Term

Effect on FractionalFlow of Water

injection rate increasecapillary pressure gradient increase

permeability to oil decreaseko /kw decreasecross sectional area decrease

µw /µo decreasefluid density difference decreasedip angle decrease

Fractional Flow Curves




0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

SW

f W

Information From the Fractional Flow Curve




1-Sor

f WF

Fraction of water

flowing at theflood front

SwSw at the

flood front

Average reservoir

water saturation

at breakthrough

T a n g e n t L i n

e

Tangent point

1

0

wBTSf w=1

f W

0Swi



Example 2




Solution

• Fractional Flow Curve

1. Sw = 55%

2. f w = 82.5%

3. = 63%

4. 5375.02.01

2.063.0E

D

wBTS

Waterflood

P f Effi i i




Performance Efficiencies

Recovery efficiency

ER = Ep EI ED

= Ev ED

= E A EI ED

Performance Efficiencies




Displacement efficiency (ED)

wi

wiwBT D

S S S E

−−=

1

Areal Sweep Efficiency (E A)




Areal Sweep Efficiency (EA)

EA

Water invaded

area

Producer

Injector

Areal Sweep Efficiency (E A)




Fraction of the horizontal plane of the reservoir that is

behind the flood front at a point in time

Factors affecting E A

• Mobility ratio• Well spacing

• Pattern geometry• Areal heterogeneities

Mobility Concept




Mobility

viscosityfluid

fluidtorock of ty permeabilimobility =

Mobility Ratio




wro

orw

o

ro

w

rw

k

k

k k

k k

Oil of MobilityWater of Mobility M

µ

µ

µ

µ

*

*==

=

Mobility Ratio Effects




M = 1 Neutral Water and oil moveequally well

M < 1 Favorable Oil will move easier than water

M > 1 Unfavorable Water will moveeasier than oil

Areal Sweep Efficiency




Pattern geometry influences areal sweep efficiency

Correlations exist for common pattern geometries as a

function of mobility ratio.

Vertical Sweep Efficiency




INJECTION PRODUCTION

EI

=

Factors Affecting Waterflooding




Gravity

Barriers to vertical flow

Lateral pay discontinuitiesCompletion interval inconsistencies



Barriers To Vertical Flow




Depositional

• Shale streaks

• Lithology changes

• Evaporite streaks

Diagenesis

• Cementation

• Dolomitization

Lateral Pay Discontinuities




Producing

well

Injection

well

Trapped oil

Lateral Pay Discontinuities




Effect of infill drilling

Producing

well

Injection

well

Infill

well

Completion Interval Inconsistencies




Producing

well

Injection

well

TrappedOil - Completions

Trapped oil -

lateral pay

discontinuities

Prediction Methods




Analytical methods

• Typically single-layer, single-pattern, iso-properties• Requires scale-up of answers to get full field results

(Buckley-Leverett, Stiles, Craig-Geffen-Morse, Dykstra-

Parsons)

• Largely replaced by numerical methods such as 3-

dimensional, 3-phase computer reservoir simulation

Development Philosophy




Understand the reservoir

Start waterflooding early

Infill drill to reduce effects of lateral pay discontinuities

Develop field on pattern waterflood

Open all of the pay in all wells

Operating Philosophy




Keep producing wells pumped off

Inject below formation parting pressure

Inject clean water

Manage waterflood by injection well tests

Conduct a surveillance program

Producing Well Operations




PWF = 1000 psi

Well notpumped off

Wellpumped off

PR = 1500 psi

PR = 500 psi

PWF = 100 psi

Minimal production/crossflow Maximum production

Injection Well Operations




Inject at 50 psi below formation parting pressure

Inject clean water Keep wellbore cleaned out

• Scale

• Fill

Maintain good injection conformance



Injection Well Testing




Waterfloods are water injection projects

Therefore: manage the project by managing the water

injection wells

Injection Well Testing




Conduct periodic injection well tests to determine:

• Skin damage

•Formation parting pressure

• Injection conformance

Waterflood Surveillance




Accurate data collection

• Monthly 3-phase production well tests – Measure oil, water, & gas production during test

• Daily injection volumes & pressures

• Maintain & properly use instruments

Reservoir pressure history

References




1. Craig, F.F. Jr.: The Reservoir Engineering Aspects of Waterflooding, SPE AIME, New York (1971).

2. Dake, L.P.: Fundamentals of Reservoir Engineering , Elsevier Scientific Publishing Company, Amsterdam, Oxford, NY (1978).

3. Petroleum Engineering Handbook , H. B. Bradley (ed.), Society of Petroleum Engineers, Richardson, TX (1987).

4. Willhite, G. P.: Waterflooding, SPE Textbook Series, 3, SPE Richardson, TX (1986).

5. Driscoll, V. J.: “Recovery Optimization Through Infill Drilling – Concepts, Analysis, and Field Results,” paper SPE 4977 presentedat the 1974 SPE AIME Annual Fall Meeting, Houston, 6-9 October.

6. Barbe, J.A. and Schnoebelen, D.J.: “Quantitative Analysis of Infill Performance: Robertson Clearfork Unit,” JPT (December 1987)

1502-1601.

7. Lemen, M.A., Burlas, T.C., and Roe, L.M.: “Waterflood Pattern Realignment at the McElroy Field: Section 205 Case History,”

paper SPE 20120 presented at the 1990 SPE Permian Basin Oil and Gas Recovery Conference, Midland, TX, 8-9 March.

8. Wu, C.H., Laughlin, B.A., and Jardon, M.: “Infill Drilling Enhances Waterflood Recovery,” JPT (October 1989) 1088-1095.9. Suttles, D.J. and Kwan, G.W.L.: “Pattern Size Reduction: A Reservoir Management Tool for Prudhoe Bay Waterfloods,” paper

SPE 26117 presented at the 1993 SPE Western Regional Meeting, Anchorage, 26-28 May.

10. Kern, C.A. and Schepel, K.J.: “Formation Evaluation Aids Application of Sequence Stratigraphy to Optimize Production of the

Means San Andres Unit, Andrews Co., TX,” 1991 SPWLA Annual Logging Symposium, 16-19 June.

11. George, C.J. and Stiles, L.H.: “Improved Techniques for Evaluating Carbonate Waterfloods in West Texas,”JPT

(November1978) 1547-1554.

12. Patton, C.C.: Applied Water Technology , Campbell Petroleum Series, Norman, OK (1986).

13. Patton, C.C.: “Water Quality Control and Its Importance in Waterflooding Operations,” JPT (September 1988) 1123-1126.

14. Robertson, D.C. and Kelm, C.H.: “Injection-Well Testing to Optimize Waterflood Performance,” JPT (November 1975) 1337-

1342.

15. Kelldorf, W.F.N.: “Radioactive Tracer Surveying – A Comprehensive Report,” JPT (June 1970) 661-669.

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H (I-4) Oil Displacement Concepts