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Wettability alteration of carbonate rock mediated by biosurfactant produced from
high-starch agricultural effluents
University of Kansas: Mehdi Salehi, Stephen Johnson and Jenn-Tai Liang
Idaho National Laboratory: Sandra Fox and Gregory Bala
9th International Wettability Symposium
Bergen, Norway. 18-19 September 2006
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Outline
Introduction Surfactin and benchmark surfactants Static adsorption Aging procedure Wettability tests Conclusions Future and ongoing work Acknowledgments
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Introduction
Spontaneous imbibition of water is the main production mechanism in naturally fractured reservoirs (NFR)
NFRs are mostly oil-wet or mixed-wet (Roehl et al. 1985).
Secondary production is very low, especially if the fractures form a connected network (Allan et al. 2003)
Low-concentration surfactants can change the wettability of the reservoir rock to a more water-wet state, promoting the spontaneous imbibition of water
Cheap biosurfactant may be an economical option
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Effectiveness of surfactant-based EOR depends on surfactant propagation through reservoir
Dilute solutions of biosurfactant assessed for:– effectiveness in mediating wettability of carbonate rocks– adsorption
Compared to similar benchmark chemical surfactant
Oil
Surfactant
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Biosurfactant
Surfactin– anionic cyclic lipopeptide – surfactant and antibiotic
properties Bacillus subtilis
– grow on high-starch medium (agro-industry waste stream)
– centrifuge to remove cells– HCl to precipitate surfactin– centrifuge and freeze-dry– re-dissolve in RO-water as
required Characterized by Schaller et al.
(INL)
O
N O
N
O
NO
N
O
NO
N
O
N
OO
O
OO
OGlu
Leu
Leu
Val
Asp
Leu
Leu
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Benchmark chemical surfactants
Similar charge Comparable tail length Prior study and/or use Candidates:
– sodium dodecylbenzene sulfonate (BIO-SOFT D40)
– sodium dodecyl sulfate (STEPANOL)
– sodium laureth sulfate (STEOL CS-330)
O
S
O
OO
Na+
S
O
OO
Na+
O
O
O
O
SO
O
O
Na+
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Selecting the chemical surfactant
IFT between surfactants and Soltrol 130
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Materials
Benchmark surfactant: STEOL CS-330 (Stepan Co.) Biosurfactant: Crude surfactin (INL) Adsorbents (53 to 300 m) :
– Miami oolitic outcrop (MI)– Bethany Falls oomoldic outcrop (BF)– Lansing-Kansas City oomoldic reservoir material (L7) from the
Hall-Gurney Field in Russell County, KS.
Surfactant-ion selective combination electrode used to determine concentration of anionic surfactants in aqueous solution by potentiometric titration with Hyamine 1622.
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Potentiometric titration
mV
--
mV
--
++
mV
--
++
++
A: Before equivalence B: At equivalence C: After equivalence
Modified after DIN EN 14480
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Surfactant electrode
.
-20
0
20
40
60
80
100
120
140
160
0 1
0.05 M Hyamine 1622, ml
E, m
V
0
100
200
300
400
500
600
De
riv
ati
ve
E, mV
First Derivative
A B C
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Static adsorption
Procedure: – 2.0 g crushed rock– 30 ml surfactant solution– shake for 24 h– centrifuge @ 3000 rpm for 30 min.– measure surfactant concentration before and after
equilibrating with crushed rock– calculate specific adsorption (mg/g)
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0
5
10
15
20
25
0 1 2 3 4
Rock Mass (g)
Sp
ec
ific
Ad
so
rpti
on
(m
g/g
)
0.37 mmol/l Surfactin on Miami
0.37 mmol/l Surfactin on BF
1.44 mmol/l STEOL on Miami
1.44 mmol/l STEOL on BF
Specific adsorption at various surfactant/adsorbent mass ratios
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0
1
2
3
4
5
0 0.5 1 1.5 2 2.5 3
Initial Concentration (mmol/l)
Sp
ecifi
c A
dso
rptio
n (m
g/g
)
0.5 g
1.0 g
2.0 g
3.0 g
STEOL CS-330 isotherms on BF rock
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STEOL and surfactin isotherms on 2.0 g BF and L7 rocks
.
0
1
2
3
4
5
6
0 0.5 1 1.5 2
Initial Concentration (mmol/l)
Sp
ecif
ic A
dso
rpti
on
(m
g/g
)
Surfactin & BFSTEOL CS-330 & BFSurfactin & L7STEOL CS-330 & L7
STEOL and surfactin (30 ml) adsorption isotherms on 2.0 g BF and L7 rocks
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Adsorption results (I)
Higher adsorption on oomoldic material– higher specific surface area
Specific adsorption as rock mass – settling of crushed rock in the test tubes reduced contact with
surfactant? higher shaking rates adsorption
– mechanical scouring of surface
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Adsorption results (II)
Specific adsorption– surfactin > STEOL CS-330– maximum adsorption density reached at a lower
concentration reflects the lower CMC of surfactin
Surfactin and STEOL CS-330 on both L7 and BF rocks exhibit the four regions seen in a typical adsorption isotherm
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Four regions of adsorption isotherm
.
0
1
2
3
4
0 0.5 1 1.5 2 2.5 3
Concentration
Sp
ec
ific
Ad
so
rpti
on
(m
g/g
)
I
II
IIIIV
Regions of typical adsorption isotherm
After Tabatabai et al. (1993)
HMC
CMC
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Explanation for regions of adsorption isotherms
After Somasunduran et al. in Sharma (1995)
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Wettability change
Clean crushed rocks– THF, chloroform, methanol, water– strongly water-wet
Age crushed rocks in crude oil – two weeks at 90C – strongly oil-wet
Change in wettability due to surfactants– contact aged rock with surfactants – assess wettability
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Qualitative wettability tests
Two-phase separation (Somasundaran & Zhang 1997)– 0.2 g of crushed rock– 20 ml RO-water – 20 ml Soltrol 130– shake for 1 min by hand and allow to settle– material partitions between aqueous/non-aqueous phases
Flotation test (Wu et al. 2006)– 0.2 g of crushed rock– RO-water– oil-wet material floats
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LKC reservoir rock – two-phase separation and flotation tests
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Bethany Falls oomoldic outcrop - two-phase separation and flotation tests
.
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Wettability tests results
Two-phase separation and flotation tests agree Surfactin more effective than STEOL CS-330 in
reversing the wettability of oil-wet crushed carbonate rocks.
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Conclusions
Standardize and report mass of rock and volume of surfactant solution used to develop adsorption isotherms
STEOL CS-330 and surfactin exhibit typical adsorption isotherms with four distinct regions
Surfactin has higher specific adsorption on carbonate rocks than STEOL CS-330
Surfactin is more effective than STEOL CS-330 in altering wettability of crushed BF and LKC carbonates from oil-wet to water-wet state.
– on both molar and w/w bases
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Ongoing and future work
Ongoing– Assess other chemical surfactants– Spontaneous/forced imbibition in cores
Future– Dynamic adsorption/desorption experiments– Economic analysis
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Acknowledgements
Co-authors:– Mehdi Salehi (PhD candidate, KU)– Jenn-Tai Liang (PI, KU)– Gregory Bala (Co-PI, INL) – Sandra Fox (INL)
Other team members– Karl Eisert (MS candidate, KU)– Vivian Lopez (Undergraduate, KU)
Financial support– Grant # DE-FC26-04NT15523
United States Department of Energy (National Energy Technology Laboratory/Strategic Center for Natural Gas and Oil)
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Contact details
Stephen J. Johnson The University of Kansas
Tertiary Oil Recovery Project Learned Hall, Room 4165E 1530 W. 15th Street Lawrence, KS 66045-7609
+1 (785) 864-3654 +1 (785) 864-4967 [email protected]