The Surfactant CTAB At Interfaces Studied ByBroadband Vibrational Sum Frequency Generation

Patrick L. Hayes and Franz M. GeigerNorthwestern UniversityDepartment of Chemistry

Evanston, IL

International Symposium on Molecular Spectroscopy62nd Meeting

June 20th, 2007

Application of surfactants to oil recovery

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ls

20001980196019401920Year

U.S. Crude Oil Production:

Kern River Oil Field near Bakersfield, California.Taken from: Jad Mouawad, “Oil Innovations Pump New Life Into Old Wells” The New York Times, March 5th, 2007.

Average oil recovery rates are 20 to 40%of field’s total oil!

U.S. Department of Energy http://www.fossil.energy.gov/programs/oilgas/eor/index.html (Accessed June 2007)

Adapted from: Energy Information Administrationhttp://www.eia.doe.gov/

Arctic National Wildlife Refuge

Application of surfactants to oil recovery

Surfactant containing fracturing fluids can improve recovery rates to 30 to 60%.

Taken from: Armstrong, K. et al. “Advanced Fracturing Fluids Improve Well Economics” Oilfield Review, Autumn 1995.

FracturedUnfracturedCrude flows through poresin well wallinto fractures.

SandstoneSand-stone

WellBore

WellBore

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Adapted from: Energy Information Administrationhttp://www.eia.doe.gov/

U.S. Department of Energy http://www.fossil.energy.gov/programs/oilgas/eor/index.html (Accessed June 2007)

Chemical Questions Regarding Fracturing Fluids

Are surfactants retained in the pores of the sandstone matrix?

Under what conditions do monolayers form? Bilayers? Multilayers?(Potential experimental parameters: ionic strength, pH, [surfactant], etc.)

Scanning electron microscope image of oilfield sandstone:

http://www.geos.ed.ac.uk/research/subsurface/diagenesis/quartz.html

Pore

Quartz Grain

CTAB at the fused quartz/water interface1) Real-time monitoring of CTABadsorption at the fused quartz/water interface using Second Harmonic Generation (SHG).

Taken from: Velegol et al. Langmuir 2000, 16, 2548.

AFM images of adsorbed CTAB layers. 2) Characterization of adsorbed surfactant structure throughsum frequency generation (SFG).

Fused Quartz

+

+

++ + + +

+

Fused Quartz

+ + + + + + + + + + +

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Fused Quartz

+ ++

Fused Quartz

++

+

++ + +

+

+

+

NCH3+

BrŠH3C CH3

Cetyltrimethylammonium Bromide (CTAB)

SHG -- Experimental setup

Hayes, P. L. et al. J. Phys. Chem. 2007, ACS ASAP.Gibbs-Davis, J. M.; Hayes, P. L.; Scheidt, K. A.; Geiger, F. M. J. Am. Chem. Soc. 2007, 129, 7175.

Teflon Reservoir

Aqueous Phase

SiO2

Itime

PMTfsec Laser

Inject CTAB

SHG -- The (3) technique

E 2 (2) E w

2 (3) E w2 o

o 2kBTze

arcsinh 2kBT[Electrolyte]

1/2

Fused Quartz

+

+

++ + + +

+

Fused Quartz

+ + + + + + + + + + +

+++++++++++

Fused Quartz

+ ++

Fused Quartz

++

+

++ + +

+

+

+

More negative surface charge Less negative surface charge

Salafsky, J. S.; Eisenthal, K. B. J. Phys. Chem. B 2000, 108, 3376. Xiao, X. D.; Vogel, V.; Shen, Y. R. Chem. Phys. Lett. 1989, 163, 555.Zhao, X.; Ong, S.; Wang, H.; Eisenthal, K. B. Chem. Phys. Lett. 1993, 214, 203.

Gouy-Chapman Model:

SHG -- CTAB adsorption experiments

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3.5S

HG

E-F

ield

(a.u

.)3.02.52.01.51.00.50.0

[CTAB] (mM)

Adsorption Isotherm (pH=6)400 mM NaCl

Surface saturation occurs at ~1.5 mM CTAB

CTAB CMC

Adsorption Trace (pH =6.5)0.5 mM CTAB400 mM NaCl

400 mMNaCl

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SFG -- Experimental setup

Mono/CCD

Delay Stage

IR: 3-10 m

Visible: 800 nm

Stokes, G. Y. et al. J. Am. Chem. Soc. 2007, ACS ASAP. Voges, A. B. et al. J. Phys. Chem. B 2004, 108, 18675.Voges, A. B. et al. J. Phys. Chem. C 2007, 111, 1567.

Sample Preparation:(1) Exposed glass slide to 5-mM solution of CTAB for 2-hours.(2) Removed and dried under N2 gas.

Following similar procedure, adsorbed layer thickness of 1.4(2)-nm determined for silica/air interface.(From Eskilsson et al. Langmuir 1998, 14, 2444.)

SFG Spectra

Assignments based on literature assignments for IR and Raman spectra.2858 cm-1: Symmetric CH2 stretching mode2880 cm-1: Symmetric hydrocarbon CH3 stretching mode2937 cm-1: Symmetric CH3-(N+) stretching mode2958 cm-1: Anti-symmetric hydrocarbon CH3 stetching mode

Sau, T. K.; Murphy, C. J. Langmuir 2005, 21, 2923. Campbell, R. A.; Parker, S. R. W.; Day, J. P. R.; Bain, C. D. Langmuir 2004, 20, 8740.Wang, W.; Gu, B.; Liang, L.; Hamilton, W. A. J. Phys. Chem. B 2004, 108, 17477.Kung, K. S.; Hayes, K. F. Langmuir 1993, 9, 263.

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SSP

H3C NH3C CH3

CH3++

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PPP

SFG Spectra

PPP Spectrum:2890 cm-1: Fermi resonance of the symmetric CH2 stretch2956 cm-1: Anti-symmetric hydrocarbon CH3 stetching mode (Present in both SSP and PPP)2967 cm-1: Combination of anti-symmetric CH3 hydrocarbon stretch and symmetric CH3-(N+) stretch. Sau, T. K.; Murphy, C. J. Langmuir 2005, 21, 2923. Campbell, R. A.; Parker, S. R. W.; Day, J. P. R.; Bain, C. D. Langmuir 2004, 20, 8740.Wang, W.; Gu, B.; Liang, L.; Hamilton, W. A. J. Phys. Chem. B 2004, 108, 17477.Kung, K. S.; Hayes, K. F. Langmuir 1993, 9, 263.

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SSP

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CH3++

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PPP

SFG Spectra

Sau, T. K.; Murphy, C. J. Langmuir 2005, 21, 2923. Campbell, R. A.; Parker, S. R. W.; Day, J. P. R.; Bain, C. D. Langmuir 2004, 20, 8740.Wang, W.; Gu, B.; Liang, L.; Hamilton, W. A. J. Phys. Chem. B 2004, 108, 17477.Kung, K. S.; Hayes, K. F. Langmuir 1993, 9, 263.

2967 cm-1: Combination of anti-symmetric hydrocarbon stretch and symmetric CH3-(N+) stretch.

+ + +

Fused Quartz

+

++++

2967 cm-1 mode consistent with interdigitated CTA+ bilayer (observedpreviously in literature.)

Conclusions & Future Work1) Use deuterated CTAB to verify assignments in SFG spectra.

H3C ND3C CD3

CD3+

2) Further SFG studies of CTAB at quartz/water interface to compliment current work at quartz/air interface. In particular, probe for further evidence of interdigitated bilayer structures (or othersurface structures) at these interfaces.

+

Fused Quartz

Water

Conclusions & Future Work3) Proof-of-concept: (3) technique can be used to track surfactant

adsorption to the fused quartz/water interface, and will be used todetermine conditions under which adsorption is reversible.

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0.5 mM CTAB400 mM NaCl

400 mMNaCl

Optimizing conditions for surfactant removal (desorption) in oil wells allows for improving recovery rates up to and beyond 60%!

Sandstone

WellBore

Acknowledgements

FundingSchlumberger Oilfield Chemical ProductsNorthwestern UniversityThe Alfred P. Sloan Foundation

The Geiger Group

http://www.chem.northwestern.edu/faculty