--> Abstract: Biology, Reservoir Engineering, And Geophysics - Hydrates May Make Strange Bedfellows, by D. M. Weinberg, M. Delwiche, and F. S. Colwell; #90928 (1999).

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WEINBERG, D. M., M. DELWICHE, and F. S. COLWELL
Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID

Abstract: Biology, Reservoir Engineering, and Geophysics - Hydrates May Make Strange Bedfellows

This paper reports experiments conducted in our laboratory to demonstrate possible connections between microbiological methane production, relative-permeability effects, and development of bottom simulating reflectors. Conceptual and numerical models suggest that pressure seals within ocean-bottom homogeneous shale sediments can be attributed to the exsolution of methane at a particular isotherm. Because isotherms and the resulting pressure seals are proposed to cross lithologic boundaries, seismic effects and bottom simulating reflectors should do likewise. The goal of our research was to determine if microorganisms could be directly involved in methane exsolution at sedimentary isotherm. Methanogens were cultured at pressures and temperature to simulate conditions in or below hydrate or free-gas zones such as identified in the Gulf of Mexico. After suitable incubation times, cultures were evaluated for growth by direct microscopy and methanogenic activity by methane gas production. Results indicated that methanogens can survive and produce methane under conditions of temperature and pressure equivalent to sediment depths at or below the hydrate stability phase boundary. Methane production under these conditions implies methane super-saturation, which would be accompanied by exsolution and gas entrapment, and consequently an identifiable seismic response. The role of microorganisms in the hydrate-formation process is critical to our understanding of the whole hydrate story.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas