HR: 16:45h
AN: GP34A-04 INVITED     [Abstracts]
TI: The application of borehole resistivity measurements to fluid flow processes at Hydrate Ridge, Oregon
AU: * Weinberger, J L
EM: jlweinbe@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr. #0244, La Jolla, CA 92093-0244 United States
AU: Brown, K M
EM: kmbrown@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr. #0244, La Jolla, CA 92093-0244 United States
AB: Borehole resistivity measurements acquired during Ocean Drilling Program (ODP) Leg 204 to southern Hydrate Ridge, Oregon document complex, fine scale (3-5 cm), hydrate filled fracture networks that differ in distribution and orientation within the different hydrologic provinces sampled. Fractures on the ridge flanks at Sites 1244-1246 have low dips (20-60°) and strike parallel to the trend of the ridge, while those on the ridge crest at Sites 1247, 1248, and 1250, are typically high-angle (>60°) with isotropically distributed strikes. Site 1251, in the eastern slope basin, lacks significant fracturing. Borehole breakouts at sites 1244 and 1245 also parallel the strike of the ridge, while those at Site 1251 are rotated perpendicular to the ridge. These differences indicate that the minimum principal stress (σ₃) direction rotates to horizontal at the ridge crest as a result of the tectonic uplift and gravitational collapse of the ridge. Chaotic fracturing on the ridge crest results from the interaction of the stress state with free gas migration, which is confined to high permeability sediments and fracture zones by capillary pressure constraints. In contrast, on the ridge flanks well ordered fractures that agree with stress orientations determined from borehole breakouts result from an obliquely dipping σ₃ and the predominance of aqueous, rather than gaseous, flow. The heterogeneity of hydrate distribution at all scales combined with the inherent instability of a collapsing ridge make Hydrate Ridge a poor target for resource development.
DE: 3004 Gas and hydrate systems
DE: 3021 Marine hydrogeology
DE: 3036 Ocean drilling
DE: 3914 Electrical properties
DE: 8010 Fractures and faults
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005