an overview of likely mechanisms - university of wyoming · low salinity waterflooding an overview...

Low Salinity Waterflooding

An Overview of Likely Mechanisms

Jill Buckley

EORI contractorAdjunct, Dept. of Chem. and Petroleum Eng.

15 January 2009

http://eori.uwyo.edu

• Additional oil recovered from some (but not all) sandstone cores.

• In studies with high permeability Berea sandstone cores, additional oil was recovered if and only if:

core contained connate water

oil phase was a crude oil

core was not “fired” to remove clays

Observations on Low Salinity Waterflooding

Recovery (% OOIP)Connate HS MS LS

Injected

HS 50 65 80

MS 50 71

LS 56 80


0

20

40

60

80

100

0 5 10 15 20 25 30 35

Brine injected, PV

Rf,

%O

OIP

0

2

4

6

8

10

12

14

ΔP (p

si) o

r pH

Test A:R1/C1WP crude oil, Swi = 40.6%q = 2.6 ft/D

R

ΔP

pH

RIB(29,690 ppm)

LSB(1,480 ppm)

16.2%



Low Salinity Flooding MechanismsUniversity of Wyoming Mechanism Workshop

12 – 23 May 2008Laramie, WY

Outside Experts:

Geoff Mason U Loughborough

Koichi Takamura BASF

Andrew Fogden Australian Nat U

Norman Morrow, Xina Xie, Li Yu, Jill BuckleyNina Loahardjo, Wang Wei, Pu Hui, Xiuyu Wang


Suggested Mechanisms• Osmotic pressure

• Limited release of mixed-wet particles

• Salinity shock

• Mineral dissolution

• Emulsification/snap-off

• Saponification

• Particle-stabilized interfaces/lamellae

• Multicomponent ion exchange

• Surfactant-like behavior

• Wettability alteration (more water-wet)

• Wettability alteration (less water-wet)

• Viscosity ratio


In a porous medium, there are multiple solid and fluid phases.

Properties of interfaces between these phases change as brine composition changes.


Proposed Mechanism

Description: Evidence for:

Evidence against: Experiments needed:


Osmotic Pressure



Rock may act as a semi- permeable membrane.

+ΔP usually associated with low salinity injected brine and increased recovery.

Increase only observed for crude oils--no increase in recovery with mineral oil

Low salinity of both connate and injected water gives very high recovery even though there is no change in salinity.

high salinityoillow salinity

Tube with corners:

Flow of oil plug depends on whether water can flow around the oil drop or high salinity phase expands.


Limited Release of Mixed-Wet Particles



Tang and Morrow (1999)p

oil

water

solid

clays

oil

clay

oil

oilwater

solid

Fines not seen in all experiments, especially BP reservoir conditions tests.

Tests to find and identify mixed-wet particles.


Salinity Shock



Changes in flowing aqueous phase composition can be amplified by step changes in injected compositions.


Vaiyda and Fogler, 1992


Salinity Shock



Changes in flowing aqueous phase composition can be amplified by step changes in injected compositions.

Often see increase ΔP and recovery with step decrease in salinity.

Secondary recovery is better for low salinity, without salinity shock.

Additional investigation of salinity gradient effects.


Mineral Dissolution



Reducing salinity increases solubility of some minerals.

Tensleep core, which does not contain clay, responds to low salinity waterflooding. Cement dissolution may release dolomite particles.

Micro CT visualization and AFM force measurements are in progress at ANU.


Tensleep rock

quartz

dolomite

Swi =20% φ=14% k=14md (HSB); 9.5 md (LSB)


Registration[1]Size 762x460x573Dry: P=7.7%; Q=79.6%; D+A=12.6%Wet: P=7.6%; Q=79.6%; D+A=12.7%

[1] Latham, S, Varslot, T & Sheppard, A. P., 2008. Image registration in Micro-CT experiments, to be submitted to the Proceedings of the Society of Core Analysts


Emulsifcation/Snap-off


5

10

15

20

25

30

35

40

45

50

55

5 15 25 35 45 55

Predicted API

°API

1.4

1.42

1.44

1.46

1.48

1.5

1.52

1.54

1.56

1.58

1.6

5 15 25 35 45 55

RI@

20°C

0

2

4

6

8

10

12

0 10 20 30 40 50 60

API Gravity

mg

KO

H /

g oi

l

0

2

4

6

8

10

12

0 10 20 30 40 50 60

API Gravity

mg

KO

H /

g oi

l

Crude Oil Composition ~ 300 Samples

ACID NUMBER

BASE NUMBER

RI vs °API

SARA vs °API


5

10

15

20

25

30

35

40

45

50

55

5 15 25 35 45 55

Predicted API

°API

1.4

1.42

1.44

1.46

1.48

1.5

1.52

1.54

1.56

1.58

1.6

5 15 25 35 45 55

°API

RI@

20°C

0

2

4

6

8

10

12

0 10 20 30 40 50 60

API Gravity

mg

KO

H /

g oi

l

0

2

4

6

8

10

12

0 10 20 30 40 50 60

API Gravity

mg

KO

H /

g oi

l

Wyoming Crude Oil Composition (20 samples)

ACID NUMBER

BASE NUMBER

RI vs °API

SARA vs °API


The Way Forward

Can we find a model rock?Reservoir cores often respond to low salinity waterflooding, but are hard to obtain, limited in quantity, heterogeneous, and sometimes poorly consolidated.

Outcrop rocks have some advantages, but have been exposed to oxidation and to low salinity rainwater. Some Berea cores (higher permeability) respond to low salinity waterflooding, but the core material that is currently available from the quarry is lower in permeability and does not respond consistently.


The Way Forward

Address baseline problem in reservoir cores

Response to low salinity my be greater in a secondary waterflood than in tertiary mode, but the baseline is shifting.


The Way Forward

Fundamental studies

Can we create a micromodel that includes kaolinite?

Force measurements in low and high salinity environments.

Micro CT visualization of particle movement.


The Way Forward

Suggestions for improved laboratory procedures

Add back pressure regulation

Add pressure measurements in imbibition tests


An Overview of Likely Mechanisms

Jill Buckley

EORI contractorAdjunct, Dept. of Chem. and Petroleum Eng.

15 January 2009


Viscosity Ratio



Is kaolin dispersed in brine or formation of emulsions increasing viscosity and sweep efficiency?

Use glycerol to viscosify brine or toluene to reduce oil viscosity.

Use a back pressure regulator to facilitate use of low viscosity oils.


Saponification



If pH of flowing aqueous phase is high enough, saponification of esters from the oil phase can cause mass transfer from oil to water and decrease IFT.

We are not seeing consistent increases in pH and pH never gets high enough to release fines or reduce IFT significantly.

An increase in pH was observed in early low salinity tests.

ester + NaOH = alcohol + organic acid

Characterization of effluent brine composition.

Crude oil compositional information.


Surfactant-like Behavior



Increasing temperature should have the same effect.

Tor Austad says adsorbed materials are surfactants, salted out by high salinity that comes off the surface in low salinity water, forms micelles or is transferred to the oil phase. Calls this “salting in.”

mixed wettingsolid

water

oil

decreasesalinity


Multicomponent Ion Exchange



BP patent: [Ca2+]inj / [Ca2+]connate < 1

Lager et al., 2006; BP patent, 2007

Secondary results for Injected = Connate.Recovery is better with low salinity even though ion exchange has already taken place.

Evidence of Ca2+ in oil? Difficult to measure.

0

5000

10000

15000

20000

25000

0 1 2 3 4 5 6 7Pore volume

Chl

orid

e co

ncen

trat

ion

(ppm

)

0

10

20

30

40

50

60

70

Mag

nesi

um c

once

ntra

tion

(ppm

)

Chloride Mg


0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

bene

fit c

ompa

re to

w

ater

flood

resu

lts (%

)

1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18

Low Salinity WaterfloodingSlide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Tensleep rockRegistration[1]Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Low Salinity WaterfloodingSlide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28

an overview of likely mechanisms - university of wyoming · low salinity waterflooding an overview...

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