Print this pageCan Fractures in Soft Sediments Host Significant Quantities of Gas Hydrates?
Thomas M. McGee1, Carol B. Lutken1, Rudy E.
Rogers2, Charlotte A. Brunner3, J.S. Dearman2,
F. L. Lynch2, and J. Robert Woolsey1
1 University of Mississippi, University, MS
2 Mississippi State University, Mississippi State, MS
3 University of Southern Mississippi, Stennis Space Center, MS
Current interest concerning what types of geologic features contain significant accumulations of gas hydrate arises from the expectation that someday commercial quantities of natural gas will be produced from hydrates. Various geologic structures within the hydrate stability zone have been imaged, seismically, but there is little consensus concerning serious candidates for exploratory drilling. Some investigators favor targeting sandy sediments where porosity and permeability are greater than in silts and clays. Others expect fractures within fine-grained sediments may host greater volumes of hydrates. The latter scenario seems to fit better with conditions in the hydrate stability zone in the northern Gulf of Mexico and with laboratory results. Hydrates have been created in the laboratory by adding natural gas, sea water and naturally occurring microbial surfactants to artificial sediments comprised of smectite, kaolinite and sand under appropriate conditions of pressure and temperature. Findings show that biosurfactants greatly enhance hydrate formation and that hydrates form preferentially on smectite (a known component of soft sediments in the Gulf) rather than kaolinite or sand. Given sufficient natural gas, all that remains to complete the formation of hydrates is a mechanism of producing a dense population of fractures open to gas and water circulation. This presentation postulates that the mechanism is polygonal faulting and provides supporting evidence.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005