The Coalbed Methane Production Potential of Tectonically Deformed and Geologically Complex Basins in the Pacific Northwest

PAPPAJOHN, STEVEN P., and TERRY E. MITCHELL, GeoTrends, Inc., Kent, WA

Most coalbed methane drilling and production activity is confined to the Warrior basin (Alabama) and San Juan basin (Colorado and New Mexico), both of which are characterized by well-documented structural and stratigraphic relationships relative to the methane-prospective coal-bearing intervals in most other basins. The coalbed methane production potential of more tectonically deformed and geologically complex basins, such as those of the Pacific Northwest where an estimated in-place methane resource potential of up to 24 tcf is thought to be present (DOE, 1981), should be demonstrated so that this resource may contribute to the energy supply of the region and the nation. All of the over 150 bcf of natural gas consumed annually in Washington must be imported from other states and Cana a.

One of the first attempts to produce coalbed methane in a structurally complex geologic setting was conducted in western Washington state. Based on exploration utilizing surface geologic mapping, data from coal corehole/test wells and underground coal mine workings (abandoned), and additional information from abandoned conventional wells, public and proprietary coal quality and rank studies, and other sources, five close-spaced coalbed methane test wells were drilled into multiple, steeply dipping coalbeds of high- to medium-volatile bituminous rank within the Eocene Puget Group. Preliminary test results and reservoir computer modeling indicate the potential for an average per-well production rate of 500 Mcf per day of pipeline-quality methane (average 950 Btu/cubic foot) from an in-p ace reserve potential of greater than 18 bcf per square mile.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)