HR: 0845h
AN: OS11C-04    [Abstracts]
TI: Gas hydrate-filled fracture distribution, eastern Indian continental margin
AU: * Cook, A E
EM: acook@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rt. 9W, Palisades, NY 10964, United States
AU: Goldberg, D
EM: goldberg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rt. 9W, Palisades, NY 10964, United States
AB: Indian National Gas Hydrate Program (NGHP) Expedition 01 was designed to study the occurrence of gas hydrate along the east and west coast of India and near the Andaman Islands. The expedition discovered gas hydrates in sand, silt, and clay dominated sediments. In this research, we study high resistivity fractures found in unconsolidated clay sediments on logging-while drilling (LWD) borehole resistivity images from four holes drilled at Site 5, Site 7 and Site 10 on the eastern Indian continental margin during NGHP Expedition 01. These fractures are likely filled with natural gas hydrate. Pressure cores from NGHP sites confirm gas hydrate commonly occurs in fracture veins in clay dominated lithology. From the LWD images, we establish the relationship between gas hydrates, fracturing, and the regional or local stress regime on the eastern Indian continental margin. Gas hydrate is identified on the borehole logs and images as high resistivity responses without associated density increases or indications of free gas. Gas hydrate saturations are calculated using Archie's equation. For gas-hydrate bearing intervals, fracture strike and dip are determined and plotted on an Equal Area steronet. The local state of stress at the time of fracturing is determined by these stereonet orientations. Fractures outside the gas hydrate bearing zones are analyzed and compared to the gas-hydrate bearing fractures. Indicators of the regional and local stress orientation based on seismic, bathymetry and other holes from NGHP are related to the fracture-derived stress orientations. Preliminary results from three of four the logging-while-drilling holes show the gas hydrate-filled fractures have an aligned, preferred orientation likely associated with the stress regime. In one hole at Site 10, where 130 m of gas hydrate-filled fractures were observed, preliminary analysis suggests the gas hydrate-filled fractures have no preferred orientation, which may result from local tectonics or diapirism.
DE: 0915 Downhole methods
DE: 3004 Gas and hydrate systems
DE: 3036 Ocean drilling
DE: 5104 Fracture and flow
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting