Coalbed Methane Production Facilities: A Case History

Abstract

SPE Member This paper describes the production facilities ARCO has recently installed to develop reserves on approximately fifty sections of land in the La Plata County, Colorado area of the San Juan Basin for producing methane gas from coal beds in the Cretaceous producing methane gas from coal beds in the Cretaceous Fruitland formation. The project involves 107 wells and is expected to reach a peak rate of 85 MMCFD (2.4 E+06 m3/d). The facilities described include artificial lift, wellhead separation, gathering systems, compression, gas treating, water disposal, field automation and corrosion protection. Operating experience is also discussed. Existing production engineering technology is adequate to economically develop these resources so long as design parameters and equipment limitations are understood. Introduction Several hundred wells have been drilled in the San Juan Basin of Colorado and New Mexico over the past ten years for the purpose of producing methane gas from coal beds. This total is expected to exceed seventeen hundred by the end of 1990 in order to capitalize on a federal tax credit allowed for developing non-conventional fuels. Amoco, Meridian, Bowen-Edwards, McKenzie Methane and ARCO have been the principal players to date. Other producers such as Phillips, Unocal, Ladd Petroleum, Richmond Petroleum, Marathon and Texaco also have a strong Petroleum, Marathon and Texaco also have a strong interest in the area. ARCO has been developing its acreage in La Plata County, Colorado since 1985 and has been encouraged by successes in this project. In the process, it is developing a better understanding of coal gas production. This paper describes the production facilities ARCO is using to develop approximately fifty sections of land in its first coal seam project. This project lies within the Southern Ute Indian Reservation in southwest Colorado. All of the ARCO acreage has been held previously by conventional gas production from deeper horizons leased from the production from deeper horizons leased from the Southern Ute Indian Tribe. These conventional wells provided an infrastructure of lease roads. However, provided an infrastructure of lease roads. However, no existing wellsites or facilities could be utilized. The project area consists of rugged terrain in the foothills of the San Juan Mountains. Surface elevations range from 6400' to 7400 (1950 to 2260 m). Arroyos cause severe changes in elevations from location to location. The pristine Animas River passes through the center of the development area. There are few inhabitants and no electrical power or other utility services within the project area. The winters are cold and the climate is semi-arid. Snowfalls of a foot or more can be expected any time between September and May. The steep, winding roads are gravel or dirt and can become impassable with only minor amounts of rain or snow. Flash floods are common in the spring and summer. Within this area ARCO was challenged to develop its gas reserves. Reservoir The Cretaceous Fruitland formation contains the thickest and most continuous coal beds within the San Juan Basin. It overlays and intertwines with the Pictured Cliff formation and is overlaid by the Kirtland Pictured Cliff formation and is overlaid by the Kirtland shale. The Fruitland formation lies about 3500' (1070 m) beneath the surface. The average net thickness of coal within the project area is about 50' (15 m). Methane and other gases are physically bound to individual coal particles. The coal seam structure consists of a coal matrix broken up by a system of natural fractures called cleats. The matrix is considered impermeable without effective porosity. The cleats give the formation its permeability. The cleats are normally completely water saturated. Gas production starts as water is drained from the cleats. As the reservoir pressure is reduced gas molecules desorb from the coal and diffuse through the matrix to a cleat. The rate of desorption increases as the reservoir pressure decreases. pressure decreases. P. 513