Laboratory Tests to Determine Role of Bioproducts in Seafloor Gas Hydrate Accumulations

Guochang Zhang, Rudy E. Rogers, and William T. French
Swalm School of Chemical Engineering, Mississippi State University, Mississippi State, MS

This study investigates possible influences of microbes in prolific gas hydrate occurrences in ocean sediments. Microbial/gas hydrate studies are reported on the laboratory production, separation and hydrate catalysis of a biosurfactant generated from Bacillus subtilis bacterium (ATCC 21332), a microbe that has been identified in Gulf of Mexico gas hydrates. Bacillus subtilis was cultured in the laboratory from 282 K to 310 K under both aerobic and anaerobic conditions. Biosurfactants were separated from the broth in foam created by bubbling gas through the mixture, and recovered from the collapsed-foam distilled-water solution by acid precipitation/dichloromethane extraction. Five surfactin isomers were identified by HPLC spectra. Natural gas hydrates were then created in porous media saturated with the recovered surfactin-water solution. According to gas-hydrate formation rate measurements, the anaerobically-produced biosurfactants catalyzed hydrate formation markedly better compared with that produced under aerobic conditions. Adsorption experiments indicated that surfactin adsorbs on the surfaces of sand, betonite and nontronite, but not on the surfaces of kaolin. In-situ visual observation of gas hydrate formation in a packing of these minerals saturated with surfactin solution also showed that gas hydrates prefer to form on sand, bentonite and nontronite rather than on kaolin clay. X-ray diffraction spectra indicated that during gas hydrate formation, surfactin adsorbed on the surfaces of bentonite particles rather than in interlayers. The tests suggest that microbial species in ocean sediments of gas hydrate stability zones could promote hydrate formation via biosurfactants produced from metabolic activities; the bioproducts could be distributed by gas flow through the sediments; the bioproducts might collect on specific minerals.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas