University of Kansas: Mehdi Salehi, Stephen Johnson and Jenn-Tai Liang

1. 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

2. Outline • Introduction • Surfactin and benchmark surfactants • Static adsorption • Aging procedure • Wettability tests • Conclusions • Future and ongoing work • Acknowledgments

3. 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

4. Oil Surfactant • 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

5. 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)

6. 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)

7. IFT between surfactants and Soltrol 130 Selecting the chemical surfactant

8. 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.

9. Potentiometric titration Modified after DIN EN 14480

10. A C B Surfactant electrode .

11. 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)

12. Specific adsorption at various surfactant/adsorbent mass ratios

13. STEOL CS-330 isotherms on BF rock

14. STEOL and surfactin (30 ml) adsorption isotherms on 2.0 g BF and L7 rocks STEOL and surfactin isotherms on 2.0 g BF and L7 rocks .

15. 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

16. 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

17. Regions of typical adsorption isotherm Four regions of adsorption isotherm CMC . HMC After Tabatabai et al. (1993)

18. Explanation for regions of adsorption isotherms After Somasunduran et al. in Sharma (1995)

19. Wettability change • Clean crushed rocks • THF, chloroform, methanol, water • strongly water-wet • Age crushed rocks in crude oil • two weeks at 90C • strongly oil-wet • Change in wettability due to surfactants • contact aged rock with surfactants • assess wettability

20. 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

21. LKC reservoir rock – two-phase separation and flotation tests

22. Bethany Falls oomoldic outcrop - two-phase separation and flotation tests .

23. 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.

24. 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

25. Ongoing and future work • Ongoing • Assess other chemical surfactants • Spontaneous/forced imbibition in cores • Future • Dynamic adsorption/desorption experiments • Economic analysis

26. 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)

27. 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 • sjohn@ku.edu