J.G. Clough1, C.E. Barker2, A.R. Scott3
(1) Alaska Division of Geological & Geophysical Surveys, Fairbanks, AK
(2) U.S. Geological Survey, Denver, CO
(3) Altuda Geological Consulting, Austin, TX
ABSTRACT: Opportunities for Coalbed Gas Exploration in Alaska
Alaska's hypothetical coal resources exceed 5 trillion short tons with estimates of coalbed methane (CBM) as high as 1037 Tcf. If only 10 percent of this gas is economically recoverable, that 10 percent would triple current proven conventional gas reserves for Alaska. The majority of coal resources, primarily Cretaceous to Tertiary in age, are spread unequally across thirteen sedimentary basins. The western Colville basin contains the greatest volume of coal with subcrops of as many as 150 significant coal seams ranging between 5 to 28 feet in thickness. North Slope CBM alone may exceed 800 Tcf. Other promising opportunities for CBM include the Cook Inlet, Nenana, Alaska Peninsula, Yukon Flats, Yukon-Koyukuk, and Copper River basins.
The Cook Inlet basin has seen increased CBM exploration activity due to declining conventional gas reserves in producing fields. In the upper Cook Inlet, net coal thicknesses up to 175 feet exist at depths of <6000 feet. CBM desorption data indicates about 60 to 240 scf/ton of gas in place. CBM resource estimates suggest ~250 Tcf for the entire Cook Inlet basin, and 8 Tcf technically recoverable gas near an upper Cook Inlet service pipeline.
Alaska coalbed gas markets include in-state urban and rural use and commercial export. Major impediments to CBM exploration and development for most basins include: absence of subsurface coalbed gas and hydrogeologic data, lack of infrastructure, and high exploration costs. We expect growth of the current Cook Inlet CBM exploration and development to lead to future commercial CBM ventures throughout Alaska.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado