GAS AND WATER PRODUCTION TRENDS OF THE RATON BASIN COALBED METHANE PLAY, NORTHEASTERN NEW MEXICO

The Raton Basin is a Laramide-age structural basin that straddles the Colorado-New Mexico state line. Coalbed methane production from Cretaceous and Tertiary coals on the New Mexico side increased sharply in 1999 following the construction of a pipeline to deliver the gas from this portion of the basin. Currently there are approximately 400 wells operated by El Paso Production Company on privately owned land in Colfax county, New Mexico, and Las Animas county, Colorado. Coal seams of the Upper Cretaceous Vermejo Formation and the Cretaceous-Tertiary Raton Formation are the current targets for development, although some of the clastic units within this interval are likely gas charged and could become exploration targets in the future.

Relatively modest gas production from most wells is acceptable given the high success rate and shallow depth (~2000 feet) of the producing interval. However, marked differences in production rates, decline behavior, and water chemistry among wells in this area suggest complex hydrologic and geologic controls which preclude a simple coalbed methane reservoir description. Wells in the southwest portion of the lease are, by far, the best producers with several wells producing more than one million cubic feet of gas per day (> 1 MMCFGD) and having an average monthly production of 8 million cubic feet of gas per well. The typical well elsewhere in this lease produces less than 100,000 cubic feet of gas per day (< 100 MCFGD) and has a monthly production around 2.5 million cubic feet of gas. In addition, many of the best wells do not show the characteristic gas incline/water decline curves associated with the early production history of typical coalbed methane wells, and in fact produce very little water as compared to other wells on the lease. A number of wells throughout the lease exhibit a double peak in gas production—one occurring fairly early in the production history, and another after a period of dewatering. The first peak may represent drainage of free gas stored within the natural fracture and cleat system of the reservoir, with the second peak due to desorption of methane from the coal matrix.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.