SMITH, THOMAS N., State of Alaska, Division of Oil and Gas, Anchorage, AK; and JAMES G. CLOUGH, State of Alaska, Division of Geological and Geophysical Survey, Fairbanks, AK

ABSTRACT: Coalbed Methane Potential for Alaska

Hypothetical coal reserves for Alaska exceed 5.5 trillion short tons or nearly 1/2 of the United States' coal reserves. These coals could contain up to 1,000 TCF of gas, yet the coalbed methane potential has not been evaluated. Most Alaska coal is subbituminous to bituminous in rank and Cretaceous to Tertiary in age. With no specific gas content measurements available, an evaluation of Alaska coal must be based on coal rank, present-day burial depth, seam thickness, and structure. Preferred coalbed methane targets have thermally mature coals (Ro >0.6%) at relatively shallow depths. Using these criteria, ten coal basins were evaluated.

Much of the Cook Inlet-Susitna, North Slope, Tanana, Nenana, Yukon, and Copper River basins contain thermally immature coals (Ro <0.5%) and have low coalbed methane potential. The Upper and Lower Koyukuk and Kobuk basins contain high-volatile bituminous coal with seams up to 17 feet thick, but they may be too structurally deformed to be prospective. The Bering River coals near the Gulf of Alaska are low-volatile bituminous to anthracite in rank and are tightly folded making large prospects difficult to find. On the Alaska Peninsula, thermally mature (Ro = 0.55%-1.76%), moderately folded and faulted coalbeds up to seven feet thick have moderate coalbed methane potential. Thermal maturity and coal isopach maps indicate the Matanuska Valley area of the Cook Inlet basin and the foothil s belt of the North Slope basin contain abundant, high rank (Ro >0.6), thick coalbeds (to 50 feet) at shallow depths giving these areas high coalbed methane potential.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.