HR: 17:05h
AN: NS54A-04    [Abstracts]
TI: Fracture-controlled Gas Hydrate Systems in the Gulf of Mexico
AU: * Cook, A E
EM: acook@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964, United States
AU: Goldberg, D
EM: goldberg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964, United States
AU: Kleinberg, R L
EM: kleinberg@slb.com
AF: Schlumberger-Doll Research, One Hampshire Street, MD-A475, Cambridge, MA 02139, United States
AU: Collett, T S
EM: tcollett@usgs.gov
AF: USGS - Denver Federal Center, Box 25046, Denver, CO 80225,
AB: We present new results illustrating that permeable fractures control the presence of natural gas hydrate in low permeability marine muds on continental margins. We analyze logging-while-drilling resistivity images acquired during the Department of Energy/Chevron Joint Industry Project in the Gulf of Mexico. A strong correlation exists between local geologic constraints and natural gas hydrate formation in marine sediments at Keathley Canyon Site 151, drilled during this project. We find that gas hydrate accumulated at Site KC151 in two modes: filling high- angle fractures and sub-horizontal permeable beds. High angle hydrate-filled fractures are the most common depositional mode for gas hydrate at this site, accounting for 93% of fractures. A total of 5 m of hydrate-filled beds were distributed throughout the hole and usually occurred adjacent to hydrate-filled fractures. This suggests natural gas traveled primarily through the fractures and only a small distance through bedding layers. Most of the hydrate-filled fractures found at Site KC151 dip at angles greater than 40 degrees and occur between 220-300 meters below seafloor. This hydrate-filled fracture interval correlates to significant natural gas hydrate saturations between 15% and 40%, as determined by Archie’s saturation equation. All fractures at Site KC151 strike approximately N-S and dip easterly or westerly. This orientation is consistent with the 165SE- 345NW maximum horizontal stress determined from borehole breakouts. The maximum horizontal stress aligns with local topography. In one interval of hydrate-filled fractures porosity increases with hydrate saturation, indicating that high pore pressure may have dilated the sediments and the formation of gas hydrate may have forced fractures apart. Results from Site KC151 will be compared to other fracture-controlled hydrate systems on continental margins, including Cascadia Margin and the Indian continental margin.
DE: 3004 Gas and hydrate systems
DE: 3036 Ocean drilling
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 5104 Fracture and flow
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly