Spe-130726-Recent Developments and Updated Screening Criteria of Enhanced Oil Recovery Techniques

7/27/2019 Spe-130726-Recent Developments and Updated Screening Criteria of Enhanced Oil Recovery Techniques

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SPE 130726

Recent Developments and Updated Screening Criteria of Enhanced OilRecovery Techniques

Ahmad Aladasani1,2

, SPE; Baojun Bai2, SPE

1.Kuwait Oil Company, 2. Missouri University of Science and Technology

Copyright 2010, Society of Petroleum Engineers

This paper was prepared for presentation at the CPS/SPE International Oil & Gas Conference and Exhibition in China held in Beijing, China, 810 June 2010.

This paper was selected for presentation by a CPS/SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not beenreviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, ormembers. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print isrestricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abst ract

This paper reviews recent developments in enhanced oil recovery (EOR) techniques published in SPE conference

proceedings for 2007 to 2009. It also updates the EOR criteria developed by Taber et al. in 1996 based on field applications

reported in Oil & Gas Journal and at various SPE conferences. It classifies EOR methods into five main categories: gas-based,

water-based, thermal, others, and combination technologies. New developments in EOR techniques, chemicals, and mechanisms

are summarized to clarify advances in EOR criteria beyond previous limitations. Reservoirs that had previously been ruled out

based on specific reservoir conditions are now candidates under updated EOR screening criteria. To demonstrate this potential,

this work has established guidelines for the selection and optimization of chemical EOR methods for a specific reservoir.

Introduction

Crude oil is found in underground porous sandstone or carbonate rock formations. In the first (primary) stage of oil

recovery, the oil is displaced from the reservoir into the wellbore and up to the surface under its own reservoir energy, such as gas

drive, water drive, or gravity drainage. In the second stage, an external fluid such as water or gas is injected into the reservoir

through injection wells located in the rock that have fluid communication with production wells. The purpose of secondary oil

recovery is to maintain reservoir pressure and displace hydrocarbons towards the wellbore. The most common secondary recovery

technique is waterflooding

1

. Once the secondary oil recovery process has been exhausted, about two thirds of the original oil inplace (OOIP) is left behind. EOR methods aim to recover the remaining OOIP.2 Enhanced oil production is critical today when

many analysts are predicting that world peak production is either imminent or has already passed and demand for oil is growing

faster than supply. Of the total 649 billion barrels remaining in reservoirs in the United States (US), only 22 billion barrels are

recoverable by conventional means. However, EOR methods offer the prospect of recovering as much as 200 billion barrels of oil

from existing US reservoirs, a quantity of oil equivalent to the cumulative oil production to date.3


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2 SPE 130726

In the early 1980s, many researchers focused on EOR research because oil prices were rising unabated and there was a

dramatic need to extract oil from depleted reservoirs. During this time, most major oil companies had research centers and funded

major programs to develop new technologies. These programs resulted in production of more than 20,000 bbl/day as a result of

chemical EOR in the United States alone. However, oil prices collapsed in 1986 and hovered around $20 per barrel from 1986 to

2003. Most operators were concerned about the lower price of oil and simply did not invest in either new EOR technologies or

new ideas to extract incremental oil from existing reservoirs. However, oil prices have recently reached new highs of $60 to even

$140 per barrel, and many analysts believe that the price of oil may stabilize above $70 per barrel. In this new price environment

and under conditions of increasing world wide oil demand, few new-field discoveries, and the rapid maturation of fields

worldwide, EOR technologies have drawn increased interest. More than 400 papers on EOR have been presented at SPE

conferences within the last three years.

EOR has the potential to reclassify unrecoverable and contingent reserves. The demand for oil continues to grow, and oil

is predicted to dominate the world energy supply for the next three decades. It is more important than ever to understand lessons

learned from past EOR applications and to develop new technologies and methods. However, the application of EOR in many

major oil-producing countries remains in its conceptual stage, especially for chemical EOR methods. Taber et al. published the

EOR screen criteria in 1996 (SPE 35385 and 39234), and these have been widely cited. However, they must be updated to reflect

recent breakthroughs in conventional EOR methods as well as newly developed EOR methods such as surfactant imbibitions, in-

depth conformance-control technologies, and low-salinity water flooding. The work presented here describes the recent

development in EOR methods, updates EOR screening criteria, and provides guidance on the selection of EOR methods.

Oil Recovery Mechanisms

Two thirds of crude oil is left behind, due to both microscopic and macroscopic factors. Microscopic factors include the

various effects of oil-water interfacial tension (IFT) and rock-fluid interaction (wettability) that give rise to oil in pores and

crevices; this oil cannot be dislodged under even large applied pressures.4,5 The reservoir pore size maybe as small as 0.1 m or

less; therefore it is not surprising that IFT influences oil mobilization. The oil that is left behind after a sweep is called residual oil

saturation, expressed as Sor. Macroscopic factors include reservoir stratification with some strata showing varying permeabilities.

Thus, the displacing fluid channels through the high-permeability zones leaving oil in the low-permeability zones unswept.6,7 Even

in a uniformly permeable reservoir, uniform displacement can break down when the displacing fluid is less viscous than the crude,

a situation known as adverse mobility ratio. In places, the less viscous fluid penetrates the oil, a feature called viscous fingering.

Another important reason why oil remains unswept is the negative capillary force in oil-wet formations; this force impedes water

imbibition into pore spaces in the reservoir rock. It often occurs in carbonate reservoirs, more than 80% of which are said to be oil

wet. Other factors, such as areal heterogeneity, permeability anisotropy, and well patterns, also leave some oil unswept by water.

The oil that is unswept is called remaining oil, and its corresponding saturation is called remaining oil saturation.


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SPE 130726 3

Oil recovery is the multiplication of displacement efficiency (ED) and sweep efficiency (ES). EOR methods focus on

increasing either displacement efficiency by reducing residual oil saturation in swept regions or sweep efficiency by displacing the

remaining oil in unswept regions. Residual oil saturation is a function of capillary number, which is the ratio of viscous force to

capillary force. Typically, the capillary number for water flooding is confined to below 10-6, usually to 10-7. The capillary number

increases in effective EOR application by three magnitudes to about 10-3 to 10-4. The capillary number can be significantly reduced

by either lowering the interfacial tension or altering the rock wettability to a more water-wet surface. Although the capillary

number can be reduced by increasing the viscous forces, the reservoir fracture gradient and pressure drops across the wells are

limiting factors.2 Oil in unswept regions can be recovered by (1) increasing the viscosity of the displacing fluid, (2) reducing oil

viscosity, (3) modifying permeability, and/or (4) altering wettability.

Field Applications and Updated Screening Guidelines for EOR Techniques

The EOR criteria published by Taber et al. in 1996 are updated here in Table 1 based on 633 EOR projects reported in

TheOil and Gas Journal from 1998 through 2008 and SPE publications. It tabulates a range of oil and reservoir properties for the

various EOR methods. Updates to the EOR criteria include the addition of porosity and permeability ranges; microbial EOR,

Water Alternating Gas (WAG) miscible, and hot-water flooding as EOR methods, along with subcategories of immiscible gas

flooding. Oil property and reservoir characteristic fields were queried to determine the range of each reservoir property and the

average value of each EOR method. Boxed figures in Table 1 represent the values adopted from Taber et al. (1996). Table 1

provides guidelines; it is not intended to represent threshold limits, which can be developed only through scientific development.

Table 1:A Summary of EOR Projects - Oil Properties and Reservoir CharacteristicsSource line: [Taber et al. (1996), Anonymous (1998, 2000, 2002, 2006) ; Mortis (2004); Kottungal (2008);

Awan et al. (2006); Cadelle et al. (1980); Demin et al. (1999)]

OilProperties ReservoirCharacteristics

SN EORMethod#

Projects

Gravity

(API)

Viscosity

(cp)

Porosity

(%)

Oil

Saturation

(%PV)

Formation

Type

Permeability

(md)

Net

ThicknessDepth(ft)

Temperature

(F)

MiscibleGasInjection

1 CO2 139

28[22]

45

Avg.37

350

Avg. 2.1

337

Avg.

14.8

1589

Avg.46

Sandstone

or

Carbonate

1.54500

Avg.201.1

[Wide

Range]

1500a13365

Avg.6171.2

82250

Avg.136.3

2

Hydrocarbon

70

2357

Avg.

38.3

18000

0.04

Avg.286.1

4.2545

Avg.

14.5

3098

Avg.71

Sandstone

or

Carbonate

0.15000

Avg. 726.2

[Thin

unless

dipping]

4040[4000]

15900Avg.

8343.6

85329

Avg.202.2

3 WAG 3

3339

Avg.

35.6

0.30

Avg.0.6

11 24

Avg.

18.3

Sandstone1301000

Avg.1043.3 NC

75458887

Avg.8216.8

194253

Avg.229.4

4 Nitrogen 3

38[35]

54

Avg.

47.6

0.20

Avg.

0.07

7.514

Avg.

11.2

0.76[0.4]

0.8

Avg. 0.78

Sandstone

or

Carbonate

0.235

Avg.15.0

[Thin

unless

dipping]

10000[6000]

18500

Avg.14633.3

190325

Avg.266.6


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4 SPE 130726

ImmiscibleGasInjection

5 Nitrogen 8

1654

Avg.

34.6

180000

Avg.

2256.8

1128

Avg.

19.46

4798.5

Avg.71Sandstone

32800

Avg. 1041.7

170018500

Avg.7914.2

82325

Avg.173.1

6 CO2 16

1135

Avg.

22.6

5920.6

Avg.

65.5

1732

Avg.

26.3

4278

Avg.56

Sandstone

or

Carbonate

301000

Avg.217

11508500

Avg.3385

82198

Avg.124

7

Hydrocarbon

2

2248

Avg.35

40.25

Avg.2.1

522

Avg.

13.5

7583

Avg.79 Sandstone

401000

Avg.520

60007000

Avg.6500

170180

Avg.175

8Hydrocarbon

+WAG14

9.341

Avg.31

16000

0.17

Avg.

3948.2

1831.9

Avg.

25.09

Avg.88Sandstone

or

Carbonate

1006600

Avg.2392

2650 9199

Avg.7218.71

131267

Avg.198.7

(Enhanced)Waterflooding

9 Polymer 53

1342.5

Avg.

26.5

4000b

0.4

Avg.

123.2

10.433

Avg.

22.5

3482

Avg.64Sandstone

1.8e5500

Avg.834.1[NC]

7009460

Avg.4221.9

74237.2

Avg.167

10

Alkaline

Surfactant

Polymer

(ASP)

13

23[20]

34[35]

Avg.

32.6

6500c11

Avg.

875.8

2632

Avg.

26.6

68[35]

74.8

Avg. 73.7

Sandstone596[10]

1520[NC]

2723

3900[9000]

Avg.2984.5

118[80]

158[200]

Avg.121.6

11Surfactant+

P/A3

2239

Avg.31

15.63

Avg.9.3

1616.8Avg.

16.4

43.553

Avg.48Sandstone

5060

Avg.55[NC]

6255300

Avg.2941.6

122155

Avg.138.5

Thermal/Mechanical

12 Combustion 27

1038

Avg.

23.6

2770

1.44

Avg.

504.8

1435

Avg.

23.3

5094

Avg.67

Sandstone

or

Carbonate

[Preferably

Carbonate]

10 15000

Avg.1981.5[>10]

40011300

Avg.5569.6

64.4230

Avg.175.5

13 Steam 271

830

Avg.

14.5

5E63d

Avg.

32971.3

1265

Avg.

32.2

3590

Avg.66Sandstone

1e15000

Avg.2605.7[>20]

2009000

Avg.1643.6

10350

Avg.105.8

14 HotWater 10

12 25

Avg.

18.6

8000

170

Avg.

2002

2537

Avg.

31.2

1585

Avg.58.5Sandstone

9006000

Avg.3346

5002950

Avg.1942

75135

Avg.98.5

15[Surface

Mining]

[7]

[11]

[Zero

cold

flow]

[NC][>8wt%

Sand]

[Mineable

tarsand][NC] [>10]

[>3:1

overburdento

sandratio]

[NC]

Microbial

16 Microbial 4

1233

Avg.

26.6

89001.7

Avg.

2977.5

1226

Avg.19

5565

Avg.60 Sandstone180200

Avg.190

15723464

Avg.2445.3

8690

Avg.88

ThefollowingreportedEORreservoircharacteristicshaveextremevaluesthat impacttherespectiveaverageandrangeinTable1.

aMinimumCO2misciblefloodingdepthreportedinSaltCreekField,U.S.A.14

bMaximumpolymerflooding viscosityreportedinPelicanLake,Canada.14

cMaximumASPfloodingviscosityreportedinLagomar,Venezuela.12

dMaximumsteamInjectionviscosityreportedinAthabascaOilSands,Canada.14

eMinimumsteamInjectionpermeabilityreportedinNorthMidwaySunset,U.S.A.14

To provide a concise representation of the EOR criteria, Figures 2 through 8 show reservoir property distributions.

Extreme minimum and maximum values could adversely impact the EOR guidelines, even when averages are reported; therefore,

boxed charts to illustrate reservoir property distribution for the main EOR methods. Figures 2 through 8 show the range in which

the majority of EOR projects are located, plotted against selected reservoir properties. Light shading indicates a favorable

reservoir property range.


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SPE 130726 5

Figures in parentheses indicate number of projects.

0 10 20 30 40 50 60

MiscibleFlooding

(#212)

ImmiscibleFlooding

(#40)

SteamFlooding

(#271)

Combustion(#27)

ChemicalEOR(#70)

Figure 2 : EOR Method API Gravity DistributionSource line: [Taber et al. (1996), Anonymous (1998, 2000, 2002, 2006) ; Mortis (2004); Kottungal (2008);


ProjectConcentration

73%

66%

78%

50%

52%

48%

48%

64%

51%

51%

0 5000 10000 15000 20000

Miscible

Flooding

(#212)

Immiscible

Flooding(#40)

Steam

Flooding

(#271)

Combustion

(#27)

ChemicalEOR

(#70)

Figure 3 : EOR Method Depth DistributionSourceline:[Taberetal.(1996),Anonymous(1998,2000,2002,2006);Mortis(2004); Kottungal(2008);

Awanetal.(2006);Cadelleetal.(1980);Deminetal.(1999)]


48%

48%

64%

51%

55%


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6 SPE 130726

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Miscible

Flooding

(#212)

Immiscible

Flooding(#40)

Steam

Flooding

(#271)

Combustion

(#27)

ChemicalEOR

(#70)

Figure4:EORMethodsOilSaturationSourceline:[Taberetal.(1996),Anonymous(1998,2000,2002,2006);Mortis(2004); Kottungal(2008);



62%

67%

64%

70%

65%

0.1 1 10 100 1000 10000 100000

MiscibleFlooding(#212)

ImmiscibleFlooding(#40)

SteamFlooding(#271)

Combustion(#27)

ChemicalEOR(#70)

Figure 5: Permeability Distribution Vs EOR MethodsSource line: [Taber et al. (1996), Anonymous (1998, 2000, 2002, 2006) ; Mortis (2004); Kottungal (2008);



60%

52%

56%

53%

64%


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SPE 130726 7

0.0001 0.01 1 100 10000


ImmiscibleFlooding(#40)

SteamFlooding(#271)

Combustion(#27)

ChemicalEOR(#70)

Figure6:EORMethodsViscosityDistributionSourceline:[Taberetal.(1996),Anonymous(1998,2000,2002,2006);Mortis(2004); Kottungal(2008);



64%

58%

51%

67%

69%

0 10 20 30 40 50 60 70


ImmiscibleFlooding

(#40)

SteamFlooding

(#271)

Combustion(#27)

ChemicalEOR(#70)

Figure 7: EOR Methods Porosity DistributionSource line: [Taber et al. (1996), Anonymous (1998, 2000, 2002, 2006) ; Mortis (2004); Kottungal (2008);

Awan et al. (2006); Cadelle et al. (1980); Demin etal.(1999)]


62%

69%

76%

55%

67%


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8 SPE 130726

Figures in parentheses indicate number of projects.

Advances in EOR Technologies

Traditionally, EOR methods have been classified into four major categories: gas, thermal, chemical, and other.2 This

paper classifies EOR methods into five principle categories: gas-based, water-based, thermal-based, other, and combination

methods. It introduces the water-based methods to replace the chemical methods because of two promising technologies included

in this category low-salinity water flooding and wettability alteration. It also introduces combination methods that involve two

major EOR methods because such methods break through the limitations of single-mechanism EOR methods. Figure 9 illustrates

the various EOR methods.

Tables 3 through 5 summarize advances in EOR technologies mainly based on SPE conference proceedings for 2007 to

2009. They list EOR limitations reported by Taber et al. in 1996, and developments in EOR technologies that either break through

previous limitations or result in favorable oil recovery conditions.

0 50 100 150 200 250 300 350 400

Miscible

Flooding(#212)

Immiscible

Flooding(#40)

SteamFlooding

(#271)

Combustion

(#27)

ChemicalEOR

(#70)

Figure8:TemperatureDistributionVsEORMethodsSourceline:[Taberetal.(1996),Anonymous(1998,2000,2002,2006);Mortis(2004); Kottungal(2008);



52%

65%

64%

77%

68%


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10 SPE 130726

Table:3 GasEORMethods

Limitation(s):(Taber,J.J.,etal.1996)

Asteepdippingreservoirispreferredtopermitsomestabilizationofthedisplacingfront.

SN AdvancesinEORTechnologiesReservoirProperty

(Oil/Lithology)

Application

Studies Pilot Commercial

1

Infill

drilling

extends

the

production

plateau,

improves

existing

(MiscibleCO2Flooding)andfutureEORmethods(MiscibleWAG)

becausethedisplacingfrontremainsstabilizedinshort

distances.20,21,22

Light /SandstoneSPE108060

SPE106575

SPE

114199

CombinationsofwaterbasedEORmethodswithgasEORmethodstoovercomevolumetricsweepefficiencylimitations

2WAGisusedtoovercometheinherentlyunfavorablegasinjection

mobilityratios,whichresultinpoorsweepefficiencies.23,24,25,26

Light&Heavy/

Sandstone&

Carbonate

SPE89353

SPE25075

SPE

106575SPE113933

3

ModifiedWAGmethodsincludesimultaneouswaterandgas

injection(SWAG)andamodifiedSWAGtechniqueinwhichwateris

injectedontopofthereservoirandgasisinjectedatthebottomto

improvesweepefficiency.27,28

SPE105071

SPE124197

4

SAG,foamisinjectedintothereservoirbyalternatingslugsof

surfactantsolutionandgasinjectiontoimprovethemobilityratio

andsweepefficiencybydecreasingthegasvelocityandplugginghighpermeabilityzones.

29,30,31,32

Light /

Sandstone&

Carbonate

SPE114800

SPE110408

SPE113370OTC19787

5 ASParecoinjectedwithCO2toenhanceWAGflood.33

SPE123866

6ConformancecontrolbyapplyinggeltreatmenttoimproveCO2

floodingsweepefficiency.34,35

SPE35379 SPE35361

Table:4 ChemicalEORMethods


(a) Anarealsweepefficiencyofatleast50%onwaterfloodisdesired.

(b) Relativelyhomogenousformationispreferred.

(c) Formationchloridesshouldbe


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SPE 130726 11


(Oil/Lithology)

Application


8

IndepthconformancecontrolbyinjectingalowviscositypH

triggeredpolymersintothereservoirtoblocksweptfractures

andhighpermeabilityzones.45

Sandstone&

CarbonateSPE124773

9Preformedparticlegel(PPG)isusedforlargevolume

conformancecontroltreatments.Sandstone

Reference

(95)

Surfactants

10

SuperandviscoelasticsurfactantsprovidebothIFTreduction

andmobilitycontroloverawidetemperatureandpressure

range.46

Light/

Sandstone&

Carbonate

SPE106005

11

Thecostofchemicalsurfactanthasalwaysbeenadrawbackin

actualfieldapplication. Theuseofagriculturaleffluentto

generatebiologicalsurfactantsprovidesapossiblelowcost

alternative.47

Light/

Sandstone&

Carbonate

SPE106078

Alkaline,AlkalineSurfactant(AS),ASP

12Applicationofalkalinesurfactant(AS)floodinginahigh

temperature(119C)andhighsalinity.48

Light/

SandstoneSPE109033

13

Adverseeffectsofalkalineinjectionaremitigatedbyusing

organicalkaline,ceramiccoatingsonprogressingcavitypumps

(PCP),andweakASPsystems.49,50,51,52

Light/

SandstoneSPE109165

SPE107776

SPE104416

SPE114348

14Olefinsulfonateswhenusedwithappropriatecosurfactants,cosolvents,andalkaliyieldresultsrequiredfornear100%oil

recoveryincores.53

Heavy/

SandstoneSPE113432

Table:5 ThermalEORMethods


(a) Combustionsustainabilityisalimitation.

(b) Porositymustbehightominimizeheatlossesintherockmatrix.

(c) Sweepefficiencyispoorinthickformations.

(d) Steaminjectionislimitedtoshallowreservoirswiththick(20ft)payzonestolimitheatloss.

(e) Steaminjectionhasahighcostperincrementalbarrelandthusisnotusedforcarbonatereservoirs.


(Oil/Lithology)

Application


1

Steamassistedgravitydrainage(SAGD)followuptocyclicsteam

stimulation improveddailyoilproductioncapacityofsingle

horizontalwellfromtheinitial2040t/dto7080t/d.54

Heavy/

SandstoneSPE104406

2

RedevelopmentofanabandonedoilfieldwithSAGD.Thepower

plantwouldgeneratesteamanddeliversurpluselectricitytothe

nationalpowergrid. Wastewaterfromnearbysewageplantwill

usedtoproduceboilerfeedwater,andSAGDisexpectedto

delivermorethan100millionbblsofoil.55

Light/

SandstoneIPTC11700

3

Steaminjectionusedtoimproverecoveryofamature

waterfloodingreservoir. Steamoverridingcanimprovevertical

sweepefficiencyandthereforeenhancerecoveryto50%from

14%.56

Light/

SandstoneSPE116549

Combinations

of

water

based

EOR

methods

with

thermal

EOR

methods

to

overcome

volumetric

sweep

efficiency

limitations

4

Thermoreversiblegelformingsystemimprovestheefficiencyof

cyclicsteamtreatments. Steaminjectionconformanceis

achievedsincegelationoccursathightemperatures. Duringoil

drainage,thereservoirtemperaturedecreasesandthegel

convertsintoliquid.57

Heavy/

SandstoneSPE104330

5

Ahightemperatureslagblockingagent(withsilicateasthemain

component)wasdevelopedforsteaminjectiontopluggas

channelingpathsandimprovesweepefficiency.58

Heavy/

SandstoneSPE104426


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12 SPE 130726


(Oil/Lithology)

Application


6

ChemicaladditivesincludingSEPAareincorporatedintothe

steamtoimprovetheefficiencyofthestimulationprocessand

increaseoilrecoveryfactors.59,60

HeavySPE108398

SPE104404

7

Catalystsareusedforinsitucombustionincarbonatereservoirs

togenerateafastercombustionfront,highercombustion

efficiencyand

higher

initial

temperatures.

61

Heavy/

CarbonateSPE107946

8Appliedreactiontechnologyusesmolybdenumoleateinsteam

stimulationtoeffectivelyreduceoilviscosity.62

Heavy/

SandstoneSPE106180

9

Thevaporizedsolventwhencoinjectedwithsteamcondenses

andmixeswithoil,creatingazoneoflowviscositybetweenthe

steamandheavyoil.63

Heavy SPE122078

CombinationsofgasbasedEORmethodswiththermalEORmethodstoovercomesteamgenerationdrawbacksorimproverecovery

10

NonthermalprocessesinvolvingCO2floodingisusedin

combinationwithsteamforoilrecoverytolimitthedrawbacksof

steamgeneration.64

Heavy SPE113234

11SAGDperformanceisimprovedbyairinjectionandgasassisted

gravitydrainage(GAGD).65,66

Heavy

SPE106901

SPE110132

Promising EOR Methods

Low-Salinity Water Flooding

Low salinity water flooding (LSWF) is a new technology developed about a decade ago to improve oil recovery.

Experimental work carried out by Tang, et al. (1997) concluded that a decrease in salinity favorably altered wettability and

improved spontaneous imbibition and oil recovery by waterflooding. Alotaibi, et al. (2009) concluded that optimal salinity

should be maintained to maximize oil recovery pg. #6. This concept was previously highlighted by Surkalo, (1990), who stated

that the effectiveness in reducing the interfacial tension depends on the where the surfactant forms. If the salinity is high or low

the surfactant forms away from the oil-water interface pg. #6.

The mechanism of LSWF oil recovery remains unclear despite several interpretations (Boussour et al. 2009). Karoussi

and Hamouda (2007) argue that oil recovery by spontaneous imbibition does not exclusively depend on the imbibing fluid

composition, but also on the composition of the initial reservoir fluid. Akin et al. (2009) note that favorable wettability

alternations have been associated with increased recovery temperatures, whereas Strand et al. (2005) associated favorable

wettability alternation in chalks with sulfate concentrations in the injection fluid as well as with temperature. Use of an injection

fluid high in sulfate ions, such as seawater, to favorably alter wettability may have adverse effects on reservoir permeability if the

formation water contains high concentrations of barium and strontium ions. Carageorgos et al. (2009) explains the adverse effects

on permeability of injection fluid that is incompatible with the formation water.


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SPE 130726 13

Table6LowSalinityWaterFlooding(LSWF)

Description

Decreasingtheinjectionwatersalinitybyreducingthetotalsuspendedsolids(TSD)hasbeenprovedtoincreaseoilrecovery.

Mechanisms

FavorablewettabilityalternationinsandstonecoresoccurswheninjectionwaterTSDisreducedbelow6,000ppm.67,75

InterfacialtensionisreducedincarbonatecoreswhentheinjectionwaterTDSwasreducedfrom214,943ppmdownto52,346ppm.76

Limitations&Challenges

ThemechanismofLSWFoilrecoveryremainsunclear,despiteseveralinterpretations.70

TheavailabilityoflowsalinitywatersourcesisalimitingfactorinLSWFapplication.

MaximizedoilrecoveryduringLSFWrequiresoptimalsalinity68,69

toeffectivelyalterwettabilitywithoutdecreasingreservoir

permeability.75,77

Water-Alternating-Gas

WAG is a combination of alternating water-flood and gas-flood to stabilize the displacement front. The breakdown of the

water-alternating gas interface mainly due to gravity segregation or low injection pressures offsets the favorable mobility ratio and

degrades the sweep efficiency. The critical design parameters in WAG are timing and water-to-gas ratio. If excessive water is

used or flooding is prolonged, capillary trapping occurs and solvent-oil banks are broken. In the opposite case, where inadequate

quantities of water and short alternating durations are used, gas channeling occurs and an unfavorable mobility ratio degrades

sweep efficiency. Therefore, well spacing, injection pressure, and reservoir permeability variations are key WAG candidate

selection criteria. Reservoir simulation should be used to determine the optimal WAG design parameters.

Table7WaterAlternatingGas(WAG)Flooding

Description

WAGisaprocessofinjectinggasasaslugalternatelywithawaterslugtoovercometheinherentlyunfavorablegasinjectionmobilityratios.78

Mechanisms

NingandMcGuire(2004)stateImmiscibleWAGfloodinginsaturatedornearsaturatedreservoirsresultsinincrementalrecoverymainlyduetoanimprovementinsweepefficiency.Bycontrast,immiscibleWAGfloodinginundersaturatedreservoirsresultsinincrementalrecoverydue

toareduction inoilviscosityandoilswellingpg.#3. MiscibleWAGflooding insuitablecandidatereservoirsresults in incrementalrecovery

duetoareductionininterfacialtensionandimprovementinsweepefficiency.24

AppliedParameterRanges

MiscibleWAG ImmiscibleWAG

NumberOfProjectsReported:3

OilProperties

APIGravityRange: 3339

OilViscosity(cP):0.30.9

ReservoirProperties

Porosity:1124%

Permeability(md):1302000

Depth(feet):75458887

NumberofProjectsReported:11

OilProperties

APIGravityRange:9.341

OilViscosity(cP):0.17 16000

ReservoirProperties

Porosity: 1831.9%

Permeability(md):1006600

Depth(feet):26509090


Stone (1982) states WAG is often limited by vertical gravity segregation, which causes the injected gas to rise and the injected water to

migratetothebottomoftheformationpg.#2.Thislimitationcanbemitigatedbyusinghighinjectionratesorreducedwellspacing.79

Gorell(1988)suggeststhatMobilewatermayshieldinplaceoilfromcontractwiththeinjectedsolventpg.#227.Therefore,thewaterslug

sizeiscriticalinordertomaintainanoptimumbalancebetweenreducingtheoilinterfacialtensionandimprovingthesweepefficiency.80


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14 SPE 130726

Foam Flooding

Recent developments in gas-miscible EOR methods are based on mobility control. Bernard et al. (1980) cite laboratory

work conducted at New Mexico State University, concluding that foam viscosities can be expected to be proportional to gas

saturation. Therefore, gas over riding effects can be controlled during oil displacement. The same work suggested adapting this

concept to carbon dioxide-miscible flooding. Foam is a dispersed bubble in a liquid and can reduce reservoir gas permeability to

less than 1% of its original value.

Carbon Dioxide EOR and Sequestration

Recently there has been renewed interest in carbon-dioxide (CO2) EOR. Growing concerns about climate change and

greenhouse gas have increased interest in carbon capture and sequestration. CO2 EOR provides an added opportunity to increase

crude-oil production while sequestering substantial volumes of industrial CO2. The advantages of this approach in a hydrocarbon

reservoir include:82

favorable geological conditions.

seal and storage capacity.

infrastructure, available wells, and operation facilities.

more than 30 years of industry experience in CO2 injection.

The difference between the objective of CO2 EOR and that of CO2 EOR sequestration is that the former maximizes

recovery with a minimum amount of injected fluid, but the latter maximizes the amount of CO 2 retained in a reservoir by

increasing its physical trapping or solubility in reservoir fluids. Except for reservoir depth and oil viscosity, all screening

parameters specifically by Taber et al. (1996) can be used to screen a reservoir for CO2 EOR sequestration.83

Surfactant Imbibition

Surfactants can be used to lower the interfacial tension during water flooding.84,85 However, recent work has noted that

surfactants favorably alter wettability in oil-wet reservoirs. Tests reported by Flumerfelt et al. (1993) on the surfactant-based

imbibition/solution drive process for single-well treatment in low-permeability, fractured environment demonstrate that the

surfactant appears to alter the wetting state of the rock and promote imbibition significantly beyond that possible with water alone

or water with dissolved CO2 pg.# 67.

Babadagli (2003) conducted an analysis of oil recovery by spontaneous imbibition of surfactant solution on a variety of

rock types including sandstone, limestone, dolomitic limestone, and chalk; he concluded that for some rock samples the

imbibition recovery by surfactant solution was strictly controlled by the surfactant concentration pg.#1. However, the difference

in recovery rate and ultimate recovery rate between high and low interfacial tension samples can also be affected by wettability

alteration and adsorption that can vary with rock type.


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SPE 130726 15

Table8SurfactantImbibition

Description

Oilisrecoveredfromfracturedcarbonatereservoirbywettabilityalternatingwithsurfactants.88

Mechanisms

Cationicsurfactantscanrecoveroilfromchalkcoresbyspontaneouscountercurrentimbibitions.89

Anionicandnonionicsurfactantsatlowconcentrations(


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16 SPE 130726

Microbial Enhanced Oil Recovery

Microbes can be used to improve oil recovery. Microbial EOR (MEOR) has always been an attractive EOR method due

to its low cost and potential to improve both microscopic and macroscopic displacement efficiencies. However, the uncertainties,

sensitivities, and time impact of biological agents have always limited their success and the application envelope. Nevertheless,

MEOR has introduced the use of organic substitutes for chemical EOR methods; these include alkaline (Guerra et al. 2007),

surfactants (Kurawle et al. 2009), and polymers (Jiecheng et al. 2007 and Sugai et al. 2007). In addition, MEOR continues to be

successful in some field applications (Town et al. 2009).

Table10MicrobialEnhancedOilRecovery(MEOR)

Description

Microorganisms and nutrients are injected into the reservoir so that the microorganism(s) multiply and their metabolic products such as

polymers,surfactants,gases,andacidsimproveoilrecovery.98

Mechanisms

Increaseinreservoirpressure,asaresultofmicrobialgasgeneration.

Reductioninoilviscosity.

Permeabilitymodificationduetoacidicdissolutionorplugging.

Decrease in interfacial tension resulting from microbial biosurfactant generation and a decrease in the population of sulfatereducing

bacteria.

BacteriaFunctionsinMEOR100

IFTReducers

(Surfactant)

Conformance

(Polymer)

ViscosityReducers PermeabilityModifiers

(Acid)

ParaffinDepositionReducers

(Gas) (Solvent)

Acinetobacter

Arthrobacter

Bacillus

Pseudomonas

Bacillus

Leuconostoc

Xanthomonas

Clostridium

Enterobacter

Desulfovibrio

Clostridium

Zymomonas

Klebsiella

Clostridium

Enterobacter

Pseudomonas

Arthrobacter

Biosurfactants (ReportedIFTMeasurementsin

mN/m)

Reference

MixedCulture

Rhamnolipid

LipopeptideSurfactin

0.020

0.006

0.080

(Kowalewskiet

al.

2005)

(Hung,Shreve2001)

(Makkar,Cameotra1999)


ThemajorityofsuccessfulMEORprojectshavebeenappliedtoreservoirswithtemperaturesbelow55 Celsius.104

MEORprojectsaresuitedforlowproductionrateandhighwatercutreservoirs.

Inthepasttenyears,thesuccessrateofMEORprojectshasbeenabout60%.104

SurfactantadsorptiontothereservoirrockandbiodegradationadverselyimpactMEORperformance.105

Steam-Assisted Gravity Drainage

Horizontal wells achieved commercially viability in the late 1980s.106 This milestone was preceded by the development of

steam-assisted-gravity-drainage (SAGD), which consists of two parallel horizontal wells. The shallower well is injected with

steam and, at times solvent to mobilize the oil. Gravity drains the oil to the bottom well for production. SAGD was originally

discovered by Dr. Roger Butler and proved commercially successful in 1992.107 Recent developments in SAGD include the use of

solvents (Galvo et al. 2009) and air (Belgrave et al. 2007) to enhance oil recovery.


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SPE 130726 17

Table11SteamAssistedGravityDrainage(SAGD)

Description

Reis (1992) states Steam is injected into the formation through a horizontal well, and oil drains into a separate, parallel, horizontal well

locatedbelowtheinjectionwellpg.#14.

Mechanisms

Steam injection reduces the oil viscosity and causes the oil to swell. The macroscopic displacement is further improved by the density

differencebetweenthesteamandtheoil,dependingonflowregimes.(Reis1992)Theoilinterfacialtensioncouldalsodecreaseasaresultofsteamdistillation.

110


Reservoirdepth.8

Formationnetthickness.8

Payzonenetthicknessshouldbedeepenoughtodrilltwoparallelhorizontalwellsoneabovetheother.

Albahlani, Babadagli(2008)statesthatSAGDischallengedbythehighverticalpermeabilityrequirementandhighenergyconsumptionpg.#1.

Summary

EOR methods are categorized into five groups: gas-based, water-based, thermal, other and combination technologies.

The EOR selection criteria published by Taber et al. in 1996 have been updated with additional project details.

Reservoir property distributions based on published field application data have been developed as a guidance tool for

selecting main EOR methods.

Novel EOR methods and combined EOR technologies have been provided as additional options to enhance oil recovery.

The breakthrough in EOR mechanisms and the resilience of new developed chemicals extend conventional EOR methods to

a wider range of reservoirs.


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18 SPE 130726

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Documents

Spe-130726-Recent Developments and Updated Screening Criteria of Enhanced Oil Recovery Techniques