Prospecting for Gas Hydrate Accumulations using 2D and 3D Seismic Data, Milne Point, North Slope Alaska

Tanya L. Inks¹, Tim Collett², D. J. Taylor³, Warren F. Agena⁴, Myung W. Lee⁴, and Robert B. Hunter⁵. (1) Interpretation Services, 1050 17th St., Suite 1760, Denver, CO 80265, phone: (720) 932-9458, fax: (720) 932-9489, [email protected], (2) U.S. Geological Survey, Box 25046, MS-939, Denver Federal Center, Denver, CO 80225, (3) U.S. Geological Survey, P.O. Box 25046, MS 939, DFC, Denver, CO 80225, (4) U.S. Geological Survey, Box 25046, MS-939, Denver Federal Center, Denver, 80225, (5) ASRC Energy Services, 3900 C St., Suite 702, Anchorage, AK 99503

The Milne Point gas hydrate prospect delineation study was part of the U.S. Geological Survey (USGS) Alaska gas hydrate resource characterization project in association with BP Exploration (Alaska) Inc. and U.S. Department of Energy research that has helped answer questions about gas hydrate distribution and reservoir properties. The interval below the base of ice-bearing permafrost (IBPF) to just below the base of the gas hydrate stability zone (GHSZ) was analyzed. Theoretical seismic modeling of stratigraphic and fluid boundaries, including shale to gas hydrate reservoirs and shale to free gas reservoirs as well as transitional gas hydrate to free gas reservoirs have been used to understand the acoustic properties of these complex systems. Petrophysical analysis of known gas hydrates show saturations of 60-90% and porosities of 30-40%. Reservoir thickness and saturation were the primary variables used in modeling acoustic attributes and calculating potential resource volumes.

Prospective “intra”-gas hydrate-bearing reservoirs below the IBPF and within the GHSZ and free gas-bearing reservoirs trapped below gas the GHSZ were delineated by seismic attributes. Fault-bounded intra-gas hydrate prospects were identified in areas that are structurally high, and that have acoustic properties corresponding to high concentrations of gas hydrate.

The historical log analysis work conducted by the USGS in this area combined with knowledge gained from 3-D seismic attribute analysis has helped us to understand the geologic setting for these unconventional reservoirs. The Milne Point area study has successfully delineated both intra-gas hydrate and sub-gas hydrate free-gas prospects that are appropriate for potential production testing operations.