ABSTRACT: Face-Cleat Patterns in Rocky Mountain Foreland Basins, Western United States: Permeability Indicators for Coalbed Methane

TYLER, ROGER, S. E. LAUBACH, and W. A. AMBROSE, University of Texas at Austin, Austin, TX., M. A. GROUT, U.S. Geological Survey, Denver, CO., and C. M. TREMAIN, Colorado Geological Survey, Denver, CO

Coalbed methane production is controlled primarily by fracture

permeability. Closely spaced fractures commonly have one or more dominant sets (face cleat) that impart anisotropy to coal properties. In coal-bearing Cretaceous and Tertiary basins of the western United States, cleat strike is uniform over basin-scale areas, but systematic cleat-strike variations exist regionally. Face-cleat strikes are northwest and north-northeast in the San Juan; northeast, east, and southeast in the Raton; southeast and northeast in the Piceance; north-northeast and northwest in the Uinta; east-northeast and west-northwest in the Greater Green River; and variable to east and north-northeast in the Powder River basins. These face-cleat strikes are parallel to tectonic shortening directions, and are at right angles to thrust fronts. In the San Juan basin, face-clea strike domains are separated by zones that contain cleats with abruptly or smoothly varying strike. In the Raton basin, the arcuate shape of the Sangre de Cristo frontal thrust is reflected by north-to-south variation of face-cleat strikes from northeast to southeast. In the Greater Green River basin and elsewhere, low-amplitude coal-compaction folds and thrust ramps cause local variation in cleat strike. Fractures are permeability pathways for the flow of gas and water to producing wells, and they may enhance or detract from the success of well completion and stimulation techniques, such as horizontal drilling, open-hole cavitation, and hydraulic fracture treatment. Knowledge of face-cleat patterns and permeability anisotropy can guide exploration and development, completion, and stimu ation practices. For example, thick coals lacking interbedded tonsteins may be effectively drained by wells deviated at right angles to face-cleat strike. Highly friable coal in domain boundary zones may be more effectively developed with cavity-completion methods.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)