Coalbed Methane in the Upper Cretaceous Fruitland Formation, San Juan Basin, New Mexico and Colorado

Coalbed methane is playing an increasingly important role in meeting the energy needs of the United States. According to one estimate, this unconventional gas may supply 4-5% of the domestic natural gas in 1994. In the San Juan Basin, Fruitland Formation coal beds contain an estimated 43 to 49 trillion cubic feet (Tcf) of methane. This basin is the most active area of coalbed methane development and production in the United States. The San Juan Basin led the nation in coalbed methane production in 1992, when nearly 2,100 Fruitland coalbed wells produced approximately 447 billion cubic feet (Bcf) of coalbed methane-81% of the total U.S. coalbed methane production of approximately 553 Bcf.From August 1987 through July 1990, the Bureau of Economic Geology (BEG) at The University of Texas at Austin evaluated geologic and hydrologic controls on the occurrence and producibility of coalbed methane in the Fruitland Formation for the Gas Research Institute (GRI). The Colorado Geological Survey and the New Mexico Bureau of Mines and Mineral Resources participated in the research through subcontracts with BEG. Results from the first two years of research were summarized in annual reports to GRI (GRI-8810322.1 and GRI-9010014.1, respectively). A topical report submitted to GRI in 1991 (GRI-9110072) superseded those annual reports, integrating their contents with research results from the final year of the study. This publication includes all except two papers from that topical report. Themes of the omitted papers were generic; therefore, those papers were omitted to focus this publication on the San Juan Basin.The unpublished GRI contract reports had limited distribution. Their goal was the timely transfer of technology to industry. Because requests for the topical report exceeded the number of copies printed and because many of the topics covered in this research appeal to a broad audience of geoscientists and engineers, this publication was issued to increase the availability of the research results. This report discusses five areas that relate to controls on the occurrence or producibility of coalbed methane.The first topic, the tectonic setting of the San Juan Basin, reviews regional tectonic controls on depositional systems and coalbed attitude. Among the most important geologic factors affecting the occurrence and producibility of coalbed methane is the depositional setting, which is covered in the second part of this report; a chapter on the regional depositional setting of Fruitland coalbed methane is followed by two chapters describing local studies. Fracture patterns in Fruitland coal beds and adjacent strata are addressed in three chapters that discuss regional cleat trends and lineament analysis. Studies of hydrology, thermal maturity, and gas composition, are essential to understanding and predicting regional hydrodynamics and coalbed gas content and composition; these considerations are the subject of two chapters. Finally, the last topic is the integration of geologic and hydrologic studies. In this section we summarize gas and water production from Fruitland coal beds, and on the basis of the relations between production, geologic setting, and hydrodynamics, we divide the San Juan Basin into regions in which Fruitland coal beds have similar reservoir characteristics.