ABSTRACT: Coalbed Methane Production Potential in Tectonically Deformed Basins of the Circum-Pacific

Terry E. Mitchell, Steven P. Pappajohn

The U. S. has been the focal point of a significant increase in the number of wells being drilled to produce natural gas from reservoir systems that are comprised predominantly of coal. This increase in coalbed methane drilling activity has been inspired by recent enhancements in the potential economic productivity of such wells; a factor that results from the introduction of petroleum-industry engineering technology to the procedures that were developed initially by the coal industry to extract the volatile gas from mining operations.

A majority of the recent coalbed methane production programs are located in the Warrior basin of Alabama in the eastern U. S., and in the San Juan basin of Colorado/New Mexico in the mid-continent region. Engineering development in the Warrior and the San Juan basin has been facilitated by the relatively undeformed, laterally contiguous nature of the prospective coal-bearing stratigraphy. Producers have not yet been encouraged to initiate exploratory coalbed methane drilling programs in the tectonically deformed basins of the far-western U. S., or elsewhere in the Circum-Pacific region, because of the extra degree of economic risk that results from unresolved complications in defining the most effective drilling and production procedures to use in such complex geologic settings.

One of the first multi-well attempts to define the engineering parameters necessary to produce coalbed methane in the tectonically complex Circum-Pacific region is underway in the northwestern United States in the western portion of the Pacific coastal state of Washington. Five closely spaced test wells were drilled into multiple, steeply dipping coalbeds of the Eocene-age Puget Group. Preliminary test results indicate the potential for an average per-well production rate of 500 mcf/d of pipeline-quality (99% methane, up to 1003 Btu) natural gas from an in-place reserve base of greater than 5.5 bcf/km²(14 bcf/mi²).

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990