Coal and Coal Gas Resources in the Piceance Basin, Colorado

Andrew R. Scott, Roger Tyler, W. R. Kaiser, Ronald G. McMurry, and H. S. Nance

Accurate assessment and delineation of coal and coal gas resources within basins are important aspects of resource development. Previous estimates of coal resources in the Piceance Basin range from 248 to 382 billion tons, and in-place coal gas resources are generally accepted to be 84 Tcf. Assuming no depth restrictions, we estimate coal and coal gas resources to be approximately 289 billion tons and 99 Tcf, respectively.

Coal gas resources in the Piceance were calculated using two different approaches because of the topographic relief in the basin. The first method, which correlated ash-free gas content with depth, overestimated coal gas resources under topographically high areas. The second method, based on coal rank, eliminated topographic effects but underestimated coal gas resources in parts of the basin where unusually high gas contents occur owing to gas migration. Therefore, coal gas resources range between 80 and 136 Tcf, depending on the method used.

Assuming no depth restrictions, 80 percent of the coal (255 billion tons) and 75 percent of the coal gas (76 Tcf) resources are found in the lower part of the Cameo-Wheeler Fairfield coal group. The regional distribution of coal gas resources generally follows net coal trends. Maximum in-place coal gas resources exceed 60 Bcf/mi² in the deeper parts of the basin and are double the 30 Bcf/mi² previously reported.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California