Geologic Framework of the 2005 Keathley Canyon
Gas Hydrate Research Well, Northern Gulf of Mexico

Authors: D.R. Hutchinson, P.E. Hart, T.S. Collett, K.M. Edwards, and D.C. Twichell, U.S. Geological Survey, and F. Snyder, WesternGeco-Schlumberger.

Venue: American Geophysical Union’s 2007 Joint Assembly, Acapulco, Mexico, May 22-25, 2007 (http://www.agu.org/meetings/ja07/ [external site]).

Abstract: The project was located in the Casey Basin in the northern Gulf of Mexico at 1,335 m water depth. A grid of 2-D high-resolution multichannel seismic lines around the drill sites, targeted for imaging depths down to at least 1,000 m subbottom, reveals multiple disconformities that bound seven mappable seismic stratigraphic units. A major disconformity in the middle of the units stands out for its angular baselapping geometry. From the seismic and drilling data, three episodes of sedimentary deposition and deformation are inferred. The oldest episode consists of fine-grained muds deposited during a period of relative stability in the basin (Units E, F, and G). A second episode (Units C and D) consists of large vertical displacements associated with infilling and ponding of sediment. This second interval corresponds with intercalated fine and coarse-grained material in the drill hole, which sampled the thin edges of much thicker units. The final episode (Units A and B) occurred during much-subdued vertical displacement. Hemipelagic drape (Unit A) characterizes the modern seafloor deposits. The basin is mostly filled. Its sill is part of a subsiding graben that is only 10-20 m shallower than the deepest point in the basin, indicating that gravity-driven transport would mostly bypass the basin. Contemporary faulting along the basin margins has selectively reactivated an older group of faults. The intercalated sand and mud deposits of Units C and D are tentatively correlated with late Pleistocene deposition derived from the western shelf-edge delta/depocenter of the Mississippi River, which was probably most active from 320 ka to 70 ka (Winker and Booth, 2000). Gas hydrate occurs within near-vertical fractures in Units E and F of the oldest episode. The presence of sand within the gas hydrate stability zone is not sufficient to concentrate gas hydrate, even though dispersed gas hydrate occurs deeper in the fractured mud/clay-rich sections of Units E and F.

Related NETL Project: The proposed research of the related NETL project DE-AI26-05NT42496, “Methane Hydrate-Related Research and Support,” is to conduct scientific studies of natural gas hydrates to support DOE efforts to evaluate and understand methane hydrates, their potential as an energy resource, and the hazard they may pose to ongoing drilling efforts.

NETL Project Contacts
NETL – Robert Vagnetti (robert.vagnetti@netl.doe.gov or 304-285-1334)
USGS – Deborah Hutchinson (dhutchinson@usgs.gov or 508-457-2263)