Rogers, Rudy E.¹, Charles E. Woods², Tao Ding¹, Guochang Zhang¹, Jennifer L. Dearman¹, Brian Kelleher² 
(1) Mississippi State University, Mississippi State, MS

ABSTRACT: Gas Hydrate Catalysis from Biosurfactants-Bentonite Interactions that Impact Sediment Stability

This paper presents the laboratory finding that small amounts of biosurfactants catalyze gas hydrate formation in porous media containing bentonite. Hydrate decompositions at bentonite/sand interfaces were observed in the laboratory to create instability conditions by forming cavities in the bentonite or by forming fluidized sand at the sand/bentonite interface, a phenomenon dependent upon the biosurfactant type. Presence of bentonite and microbial activity, therefore, in continental slope sediments could accentuate gas hydrate instabilities. 
Surfactin, a lipopetide produced by Bacillus subtilis (a species associated with gas hydrate mounds of the Gulf of Mexico) decreases gas-hydrate induction times by as much as 71% and increases formation rates by as much as 4-fold in sand/bentonite laboratory tests. Gas hydrates are promoted by enhanced hydrocarbon gas solubility in water because of the micelles formed by some glycolipids and lipopeptide biosurfactants. The critical micellar concentrations of some of these biosurfactants decrease to as low as <20 ppm in seawater at gas-hydrate-forming-conditions. Although non-micelle-forming, polysaccharide-lipid biopolymers also function to associate the hydrocarbon gas and water on their molecular structures at hydrophobic and hydrophilic groups, respectively. Bentonite preferentially adsorbs and concentrates these and other anionic biosurfactants and biopolymers in porous media, promoting gas hydrate formation at the concentration sites. Instability conditions are created upon hydrate decomposition. 
A mechanism is postulated for the bentonite-biosurfactant hydrate formation catalysis, and a mechanism is presented for porous media instabilities developing from the hydrate decomposition.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.