Gas Hydrate Prospect Development and Production Modeling, Alaska North Slope

Robert B. Hunter¹, Timothy S. Collett², Scott J. Wilson³, Tanya L. Inks⁴, Robert R. Casavant⁵, Roy A. Johnson⁵, Mary M. Poulton⁵, Kenneth M. Mallon⁶, Shirish L. Patil⁷, and Abhijit Dandekar^7
1 ASRC Energy Services, Anchorage, AK
² U.S. Geological Survey, Denver, CO
³ Ryder Scott Company, Denver, CO
⁴ Interpretation Services, Denver, CO
⁵ University of Arizona, Tucson, AZ
⁶ Petroleum Geology Consultant, Houston, TX
⁷ University of Alaska Fairbanks, Fairbanks, AK

The U.S. Department of Energy and BP Exploration (Alaska), Inc. sponsor this gas hydrate resource assessment with the U.S. Geological Survey, the University of Arizona, and the University of Alaska Fairbanks. The USGS estimates large volumes of in-place gas (40-100 TCF) exist as hydrates beneath Alaska North Slope development infrastructure. Seismic and well data interpretation within the Milne Point Unit reveal multiple gas hydrate prospects within the fluvial-deltaic Sagavanirktok Formation shallow sands. Gas may have migrated into conventional petroleum system traps before regional geothermal gradient depression, creation of gas hydrate stability conditions, and conversion of gas and water into gas hydrate. Both structural and stratigraphic compartmentalization of gas hydrate-bearing reservoirs reduces lateral continuity of prospects and complicates the shallow velocity field, likely affecting seismic interpretation of deeper, oil-bearing targets. Production modeling of gas hydrate prospects indicates that significant volumes of gas should be technically recoverable. Models indicate the potential for economical recovery, which will be aided in areas where local uses for gas exist. Production methods involve in-situ dissociation of solid, pore-filling gas hydrate into gas and water components. Simulation models indicate that depressurization of in-situ gas hydrate from producing adjacent free gas can more than double the expected ultimate recovery available from only the free gas. Gas hydrate prospects without an adjacent free gas may also be depressurized by producing in-situ connate waters if sufficient mobile waters co-exist with gas hydrate. Thermal and/or chemical stimulation techniques are also under investigation as methods to enhance gas recovery from gas hydrate.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005