Geologic Overview, Coal, and Coalbed Methane Resources of the Wind River Basin—Wyoming

Abstract

The Wind River Basin is an east-west-trending intermontane asymmetrical syncline covering an estimated 8,100 sq mi in central Wyoming. The basin contains comparatively minor structural deformation in the form of folding and faulting. Structurally, the surrounding area is more complex, with major thrust fault zones traversing northwest to southeast over the region. Major coal-bearing strata of the Wind River Basin are contained in the Upper Cretaceous Mesaverde Formation. The area is divided into seven coal fields and regions: Muddy Creek coal field; Pilot Butte coal field; Hudson (Lander) coal field; Beaver Creek coal field; Big Sand Draw coal field; Alkali Butte coal field; and Arminto (Powder River) coal field. Their major coal deposits are found in the Mesaverde and Meeteetse Formations, along the basin perimeter. The Alkali Butte coal field contains three coalbeds greater than 4 ft thick, the most important being the Signor, Beaver, and Shipton coals, with a rank of subbituminous C. The Hudson coal field contains the Signor coalbed or zone, which has been traced some 22 mi from the Alkali Butte coal field to the east. Coal contained within his zone is ranked as subbituminous. The remaining five coal fields have not been extensively developed. Thin and split coalbeds are prevalent in a few of these fields, and in many instances top-quality coals are scattered, making it difficult to justify development. Little is known about the basin's coal resource at depth. The data collected suggest that a large part of the Wind River Basin may have some potential for coalbed methane production. However, a primary target area of about 1,500 sq mi, located in the northeastern part of the basin (Fremont County and western Natrona County) has been designated as having the highest potential for coalbed methane production. This target was determined by evaluating desorption data obtained from U.S. Geological Survey coal cores from the Wind River Basin Indian Reservation and integrating the data with coalbed geology. On the basis of this information, an estimated range of 5.2 to 2,225 billion cubic feet of gas may be contained in the Wind River Basin. Ranges for the expected inplace methane resource have been established for the coal fields of the Wind River asin, based on available data.