Zeta potential changes at mineral-brine and oil-brine interfaces control improved oil recovery during ‘smart’ waterflooding
Matthew JacksonDawoud Al-Mahrouqi, Shuai LiDepartment of Earth Science and Engineering, Imperial College London
Low salinity (‘smart’) waterflooding successesIn sandstones………
Example from RezaeiDoust et al. (2011) reproduced in Jackson et al., Fuel, (2016)
© Imperial College London
Low salinity (‘smart’) waterflooding successes
(Yousef et al., 2010)
In carbonates………
© Imperial College London
All looking rosy……but……
Example from Nasralla and Nasr-El-Din (2014) reproduced in Jackson et al., Fuel, (2016)
© Imperial College London
All looking rosy……and……
© Imperial College London
0
10
20
30
40
50
60
0 3 6 9 12 15
FMB 100dFMB
Cum
ulat
ive o
il re
cove
ry %
PVs injected
0% incremental
(Austad et al., 2011)
‘Smart’ waterflooding: what we don’t know
• Why it doesn’t always work and/or is not always repeatable
• How to identify candidate reservoirs without conducting numerous costly core-flooding experiments
• How to predict the optimum modified (controlled) injection brine composition
Jackson et al., Fuel, (2016)
© Imperial College London
Why zeta potential?Measure of electrical charge at an interface (mineral-brine, oil-brine, gas-brine etc…..)
Controls the electrostatic interactions between mineral surfaces and polar species in aqueous and non-aqueous solution
Probes mineral surface so sensitive to wetting state
Mechanisms invoked to explain improved recovery during smart waterflooding cause changes in zeta potential at mineral-brine interface
• Concentration of ‘potential determining ions’ (PDIs)• Ion exchange on mineral surfaces• Double layer expansion
Jackson et al., Fuel, (2016)© Imperial College London
Zeta potential at mineral-brine interfaces
Glover and Jackson (2010)
© Imperial College London
Sandstones and potential determining ions (PDIs)
© Imperial College London
• Zeta potential depends on pH for metal oxides (protonation and deprotonation reactions at mineral surface)
• Zeta potential also depends on adsorption of salt species onto mineral surfaces (e.g. Ca2+, Mg2+)
• ‘Indifferent’ ions do not directly interact with surface
Ishido and Mizutani, 1981
Zeta potential and double layer expansion
© Imperial College London
• Generally assumed zeta potential at mineral-brine interfaces increases in magnitude during dilution
• Zeta potential also depends on adsorption of salt species onto mineral surfaces (e.g. Ca2+, Mg2+)
Example from Vinogradov et al. (2010) reproduced in Jackson et al., Fuel, (2016)
Carbonates and potential determining ions (PDIs)
© Imperial College London
• Zeta potential depends on pH in unbuffered experiments (pCa allowed to vary)
• Zeta potential constant in buffered experiments (pCafixed)
• Proton is not a PDI for the carbonate mineral surface
Foxall et al., 1979
Carbonates and potential determining ions (PDIs)
-20
-15
-10
-5
0
5
0 0,5 1 1,5 2 2,5 3 3,5
Zeta
pot
entia
l (m
V)
pPDI
Ca Mg SO4
FMB SW
• Identical behavior of Ca and Mg within experimental error• Sensitivity to SO4 much lower (not a PDI?) AlRoudhan et al., Col. Surf. A, 2016
Carbonates and potential determining ions (PDIs)
-14
-12
-10
-8
-6
-4
-2
0
2
4
0 0,5 1 1,5 2 2,5 3 3,5
Zeta
pot
entia
l (m
V)
pCa
0.05M
2M
0.5M
• Sensitivity to pCa and pMg decreases with increasing total ionic strength
AlRoudhan et al., Col. Surf. A, 2016
Increasing ionic strength
Similar to 10x dilute seawater
Similar to typical formation brine
Carbonates and potential determining ions (PDIs)
0 0.5 1 1.5 2 2.5 3 3.5-12
-10
-8
-6
-4
-2
0
2
4
6
8Ze
ta P
oten
tial (
mV)
pCa
NaCl = 0.5 M
NaCl = 2 M
NaCl-EQ experiments
Estaillades
Ketton
Portland
• Different carbonates exhibit different behaviourAlMahrouqi et al., Adv. Col. Int. Sci., 2017
Ketton and Portland
Estaillades
Measurement of zeta potential: The zetameter
Example from Malvern
• Measurement of zeta potential is routine in materials science
• Off-the-shelf commercial equipment available
BUT….• Require powdered samples• Limited range of
pressure/temperature/ionic strength
• Only one fluid phase present
IN NATURE……• Intact rocks• High P/T/I• Oil + water
© Imperial College London
Experimental setup
O
BB
O
Pump
Oil reservoir
Core holder
NI Data Acquisition
System
M
P1 P2
Manometer
Confining pressure
pump
Pressure transducer
SamplingSampling
V1
V2
V3V4
V5V6
Thermocouple
Metering valve
Oven
Coiled flowline
Vinogradov et al., 2010FP
VCrww
w
j σµςε
=∂∂
==0
Typical experimental results
AlRoudhan et al., Zeta Potential of Intact Natural Limestone: Impact of Potential-Determining Ions, Col Surf A 2016
-0,99
-0,94
-0,89
-0,84
-0,79
-800
-600
-400
-200
0
200
400
600
0 1000 2000 3000 4000 5000 6000
Volta
ge, m
V
Pres
sure
, kPa
Time, s
Synthetic Formation Brine (2M, c. 250,000ppm)
-30
-25
-20
-15
-10
-5
0
5
10
Zeta
pot
entia
l (m
V)
Sst Carbonates
FMB to dilute seawater
Zeta potential in brine-saturated (water-wet) carbonates and sandstones
Link between zeta potential and wettability
Increasing oil wetnessModified from Jackson et al., Sci. Rep. (2016)
-7
-5
-3
-1
1
3
5
7
9
00,20,40,60,81
Cha
nge
in z
eta
pote
ntia
l afte
r agi
ng (m
V)
Amott Water Wetting Index (-)
Link between zeta potential and wettability
Increasing oil wetnessModified from Jackson et al., Sci. Rep. (2016)
-7
-5
-3
-1
1
3
5
7
9
00,20,40,60,81
Cha
nge
in z
eta
pote
ntia
l afte
r agi
ng (m
V)
Amott Water Wetting Index (-)
+++
++++
+++
+
+
++++
+
+
+
+++
Water wet
Water wet
+ ++ +++ ++ ++ +++
Water wet
+
Link between zeta potential and wettability
Increasing oil wetnessModified from Jackson et al., Sci. Rep. (2016)
-7
-5
-3
-1
1
3
5
7
9
00,20,40,60,81
Cha
nge
in z
eta
pote
ntia
l afte
r agi
ng (m
V)
Amott Water Wetting Index (-)
Water
Oil wet
Oil wetOil wet
Water wet
Water wet Water wet
Oil
---
-
- - - -- - -- --- -+++++
-- - - - - - -
---
++
+
Link between zeta potential and wettability
Increasing oil wetnessModified from Jackson et al., Sci. Rep. (2016)
-7
-5
-3
-1
1
3
5
7
9
00,20,40,60,81
Cha
nge
in z
eta
pote
ntia
l afte
r agi
ng (m
V)
Amott Water Wetting Index (-)
Trend indicates negative zeta potential at oil-brine interface
Link between zeta potential and wettability
Increasing oil wetnessModified from Jackson et al., Sci. Rep. (2016)
-7
-5
-3
-1
1
3
5
7
9
00,20,40,60,81
Cha
nge
in z
eta
pote
ntia
l afte
r agi
ng (m
V)
Amott Water Wetting Index (-)
Water
Oil wet
Oil wetOil wet
Water wet
Water wet Water wet
Oil
+
+ +++++++++++++++ +
+
++++ + +
++++++
++++
++++++
Trend indicates negative zeta potential at oil-brine interface
Link between zeta potential and wettability
Increasing oil wetnessModified from Jackson et al., Sci. Rep. (2016)
-7
-5
-3
-1
1
3
5
7
9
00,20,40,60,81
Cha
nge
in z
eta
pote
ntia
l afte
r agi
ng (m
V)
Amott Water Wetting Index (-)
Trend indicates negative zeta potential at oil-brine interface
Trend indicates positive zeta potential at oil-brine interface
Link between zeta potential and wettability
Increasing oil wetnessModified from Jackson et al., Sci. Rep. (2016)
-7
-5
-3
-1
1
3
5
7
9
00,20,40,60,81
Cha
nge
in z
eta
pote
ntia
l afte
r agi
ng (m
V)
Amott Water Wetting Index (-)
Trend indicates negative zeta potential at oil-brine interface
Trend indicates positive zeta potential at oil-brine interface
Sandstone
Link between zeta potential and EOR in carbonates: Conventional LSW with –ve oil
0
10
20
30
40
50
60
0 5 10 15 20 25 30 35
SPM
1
ζ F
SPM
2
ζ i(sw
)
SPM
3
ζ i(20
dsw)
Cumulative incremental oil recovery
FMB SW 20dSWCum
ulat
ive
oil r
ecov
ery
(%)
Pore volume injected, ml
Oil D
Jackson et al., Zeta potential in oil-water-carbonate systems and its impact on oil recovery during CSW, Scientific Reports 2016
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35
SP
M1
ζ F
SP
M2
ζ i(sw
)
SP
M3
ζ i(20
dsw)
FMB SW 20dSWCum
ulat
ive
oil r
ecov
ery
(%)
Pore volume injected, ml
Link between zeta potential and EOR in carbonates: Conventional LSW with +ve oil
Oil A
Jackson et al., Zeta potential in oil-water-carbonate systems and its impact on oil recovery during CSW, Scientific Reports 2016
Link between zeta potential and EOR in carbonates: Inverted LSW with +ve oil
Improved recovery with oil A by increasing salinity!Change in zeta potential is key, not change in salinity
0102030405060708090
100
0 5 10 15 20 25 30 35
SPM
1
ζ F
SPM
2
ζ i(sw
)
SPM
3
ζ i(FM
B)Cumulative
incremental oil recovery
20dSW SW FMBCum
ulat
ive
oil r
ecov
ery
(%)
Pore volume injected, ml
Jackson et al., 2016
Link between zeta potential and EOR in sandstones
0
10
20
30
40
50
0
10
20
30
40
50
60
70
0 20 40 60 80
Pres
sure
diff
eren
ce (p
si)
&pH
Oil
Rec
over
y, %
OO
IP
Pore Volume
Oil D
SW30dFMB2
0
5
10
15
20
25
0
10
20
30
40
50
60
70
0 5 10 15 20 25
Pres
sure
diff
eren
ce (p
si)
&pH
Oil
Rec
over
y, %
OO
IP
Pore Volume
Oil A
SW30d FMB2
Incremental oil recovery during conventional CSW with –ve oil is around 5.25% OOIP
Incremental oil recovery during inverted CSW with +ve oil is around 3.25% OOIP
Correlation between IOR and change in zeta potential – all experiments
Normalize the change in zeta potential resulting from CSW by the change in zeta potential corresponding to wettability alteration
Jackson et al., Sci. Rep. (2016)
FMBSorSw
FMBSw
CSWSw
FMBSw
n−==
==
−−
=11
11
ζζζζζ
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14 16
IOR
(%)
Zeta potential of oil droplets
Hexadecane droplets in 0.4 mM NaClO4Suggested that hydroxide ions charge and stabilize dropletsBut emulsions become unstable > 5mM salt (how measure zeta potential?)(from Beattie and Djerdev, 2004)
Zeta potential and CSWIf the oil-water interface has a negative zeta potential:• IOR observed by CSW to produce a more negative zeta
potential on mineral surfaces • conventional approach of diluting formation brine and/or
seawater is successfulIf the oil-water interface has a positive zeta potential:• IOR observed by CSW to produce a more positive zeta
potential on mineral surfaces • increasing the concentration of Ca or Mg ions may be
successful in carbonates
Studies that have failed to observe improved recovery using the conventional (dilution) approach to CSW may have been dealing with a positive zeta potential at the oil-water interface