USGS science for a changing world

This final report to the Department of Energy for Task DE-AT26-97FT34343 covers the period from 1997 to April, 2005 and summarizes the larger research accomplishments, which can be divided in field and laboratory experiments. The geophysical and sampling field programs include 5 experiments conducted between 1998 and 2003 in the Gulf of Mexico (four cruises) and on the Blake Ridge (one cruise). Significant results from the Gulf of Mexico include advancing knowledge of gas hydrate as a potential hazard to drilling at a time when petroleum exploration and production move into deeper water on the continental slope. Anomalous bright reflections called high-reflectivity zones (HRZ's) were identified as possible seismic indicators of gas hydrate. Subsequent sampling through coring identified how methane flux changes from vent regions into mini-basins, and could explain the lack of a known Bottom Simulating Reflection (BSR) in much of the Gulf. In conjunction with the Chevron Gulf of Mexico JIP project, two site surveys were run to characterize gas hydrate prior to drilling in 2005, including detailed analysis of a BSR reflection at one of the sites. The one cruise to the Blake Ridge collected core samples to test the origin and age of the Blake Ridge collapse feature. While the cruise results were equivocal, they results raised new questions about the timing of methane release from hydrate in this well-studied natural laboratory field site. These field programs, particularly in the Gulf of Mexico, helped further DOE goals of understanding gas hydrates in areas where deep-water drilling and production were likely to penetrate the gas hydrate stability zone. Laboratory experiments were generally integrated with field studies but addressed specific questions about methane hydrate behavior and properties. Studies in the Gas Hydrate and Sediment Testing Laboratory Instrument (GHASTLI) performed some of the first physical property measurements on hydrate-sediment mixtures at simulated in-situ temperatures and pressures. These experiments showed the importance of grain size to hydrate occurrence, and demonstrated how the technique for making hydrate can significantly affect hydrate occurrence in the sample. The thermal properties laboratory made comprehensive thermal characterization of synthetic hydrate demonstrating the linear and non-linear behavior of the material in certain parts of the hydrate stability zone. From the petrophysics laboratory came detailed measurements of physical properties of pure methane hydrate as compared to ice and other hydrocarbon hydrates. This laboratory also developed a cryogenic Scanning Electron Microscope (SEM) capability that has been used to analyze samples returned from the field programs. Most laboratory experiments also included measurements in support of the major DOE-cofunded drilling programs (ODP Leg 204, Mallik, and Hot Ice). These laboratory studies also support DOE objectives of developing well-constrained parameters to use in modeling studies