The Powder River Basin

The Powder River Basin is located in northeastern Wyoming and southeastern Montana (Figure 17). The basin covers an area of approximately 25,800 square miles, of which approximately 75% is in Wyoming. Fifty percent of the Powder River basin is believed to have the potential for CBM production.

Coal beds in this region intermingle at varying depths with sandstones and shale. The majority of the productive coal zones range from 150 feet to 1,850 feet below ground (Randall, 1991). The uppermost formation is the Wasatch Formation, extending from land surface to 1,000 feet deep. Most of the coal seams in the Wasatch Formation are continuous, but thin (six feet or less). The Fort Union Formation lies directly below the Wasatch Formation and can be as thick as 3,000 feet. The coal beds in Fort Union formation are usually more plentiful in the upper portion, named the Tongue River member. This member is normally 1,500 to 1,800 feet thick, of which a net total of 350 feet of coal can be found in various seams. The thickest of the individual coal seams is over 150 feet thick. CBM production is primarily from the Fort Union rather than the overlying Wasatch.

The Fort Union Formation supplies municipal water to the city of Gillette, WY and is the same formation that contains the coals that are developed for CBM. The coal beds contain and transmit more water than the sandstones. The sandstones and coal beds are both used for the production of water and the production of CBM. Total Dissolved Solids (TDS) levels in the


General location map and coal rank map of the Powder River Basin water produced from these coal beds meet the water quality criteria for drinking water.
The Powder River Basin is the fastest growing CBM area in the United States. The huge coal deposits contain enormous amounts of methane gas due to their unusual thickness as evident in the amount of coal produced from this region. The low gas content per ton and low pressure were initially seen as barriers to development. The first wells drilled and completed produced massive volumes of water but little gas. As companies altered their drilling to more shallow wells, production increased. The low drilling costs, the short completion time and the relatively good quality of water coupled with inexpensive water management i.e. surface discharge encouraged development.

The BLM in Montana and Wyoming issued their Final EISs for the Powder River Basin in January 2003, and they anticipate combined activity of upwards of 60,000 new wells and accompanying roads, pipelines, and electrical utilities, and compressors in the basin. Currently, there are approximately 14,000 producing wells in the Powder River Basin, mainly in the Wyoming portion.

The Raton Basin

The Raton Basin is the southern most Laramide basin in the Rockies and covers about 2,200 square miles along the Colorado-New Mexico border (Figure 18). The basin extends 80 miles north to south and as much as 50 miles east to west (Stevens et al., 1992). It is an elongate asymmetric syncline, 20,000 to 25,000 feet thick in the deepest part.

Coal beds occur in the Upper Cretaceous Vermejo and Paleocene Raton formations at depths from outcrop to more than 4,000 ft. Vermejo coal beds are lenticular and fairly continuous, with net coal thickness of 10 to 40 ft. Raton coals generally are thinner and less continuous. Most of the coal in the basin is high-volatile bituminous in rank. Measured gas contents range from less than 50 scf/ton to more than 400 scf/ton.

The coal seams of the Vermejo and Raton formations developed for methane production also contain water that meets the federal water quality criteria for drinking water. The underlying Trinidad Sandstone and other sandstone beds within the Vermejo and Raton formations, as well as intrusive dikes and sills, also contain water of sufficient quality to meet the drinking water quality criteria.

Methane resources for the basin have been estimated at approximately 10.2 Tcf contained in the Vermejo and Raton formations (Stevens et al., 1992). It was reported recently that the average CBM production rate of wells in the Raton Basin was close to 300 Mcf per day, and annual production in 2000 was 30.8 Bcf (GTI, 2002). The Unita Basin The majority of the Uinta Basin is contained within Utah, with a small segment of the basin lying in northwestern Colorado (Figure 19). The basin covers approximately 14,450 square miles (Quarterly Review, August 1993). Stratigraphically the Uinta Basin is adjacent to the Piceance Basin of Colorado, but is structurally separated from it by the Douglas Creek Arch, an uplift near the state line. It is bordered on the West by the San Rafael Swell and Uncompahgre Uplift and on the north by the Uinta Mountains. Significant down-warping of the basin occurred during the Late Creatceous and Eocene (Laramide) timeframe. Coal beds in the Uinta Basin occur in the Mesaverde Group, however the majority of development activity targets the high-volatile bituminous coals in the Ferron Sandstone member of the Mancos Shale. A 80-mile-long, 12-mile-wide, "Corridor" paralleling the thickest development (10 to 40 ft) of Ferron coal seams has been identified by the Utah Geological Survey. (uGs 1997) Sandstone is interbedded with the Ferron coals and forms a segment of elastic sediment 150 to 750 feet thick. The Ferron Sandstone coals range in depth from 1,000 to over 7,000 feet
below surface level (Garrison et al., 1997). The Blackhawk Formation comprises coal seams interbedded with sandstone in combination with shale and siltstone. Wells drilled in the Blackhawk Formation coals are finished at 4,200 to 4,400 feet below the surface (Gloyn and Sommer, 1993).

The Blackhawk Formation and the Ferron coals of the Uinta Basin have water that meets the National Primary Drinking Water (NPDW) criteria. Groundwater from the Blackhawk Formation taken at the Castlegate Field contains a TDS level below the federal drinking water standard of 10,000 mg/L. Castlegate Field coal beds have published TDS levels of 5,000 mg/L in production waters indicating that the methane gas wells in this portion of the basin are located in an aquifer that meets the NPDW standard

General location map and coal rank map of the Uinta Basin
Full scale exploration within the Uinta Basin began in
the 1990s (Quarterly Review, 1993). The CBM potential of
the Uinta Basin was estimated by the Utah Geological Survey in the early 1990s to be between 8 Tcf and 10
Tcf (Gloyn and Sommer, 1993). Total production was 75.7 Bcf in 2000 (GTI, 2002). The Ferron coals at the north end of the corridor, primarily in River Gas Utah's Drunkards Wash Unit, have produced more than 200 Bcf of methane with daily production of 260 MMcfd from 470 wells (EPA 2002b).
22 CBM Primer

OTHER BASINS
The other major basins in the Rocky Mountain region which have tremendous potential to produce vast amounts of CBM are the Denver, Greater Green River, and Piceance basins. These basins are currently being investigated by numerous development companies and it is anticipated that several federal EISs will be conducted in the next few years The majority of the Denver Basin lies in the east central region of Colorado and contains an estimated 2 Tcf of CBM (Figure 15). Development has been delayed by a deficiency in the data regarding the extent of the CBM resource and the disposition of the gas reservoirs. The two main coal formations are enclosed by four Denver basin aquifers,presenting concerns about the degree to whichthe aquifers and coals are linked hydraulically
and to what extent CBM development would have on the groundwater resources (Wray & Koening, 2001). CBM resources in the Greater Green River Basin of Colorado and Wyoming have been estimated at upwards of 314 Tcf (GTI 2001). A sizable portion of CBM resource is located at depths less than 6,000 feet. (Kaiser et al., 1995). Some exploration and limited development of CBM occurred in the late 1980s and early 1990s. indicate that approximately 31 Bcf of CBM was produced in Moffat County during 1995 (COGCC web site, 2001). There appears to be no commercial production at present. Development of CBM in the basin has lagged due to the current limited economic viability. The degree to which the lowering of the hydrostatic pressure is required in most wells has been the chief restraining factor, compounded by the depth of the coal zone and the relatively low CBM recovery potential. Recently, permits for new gas wells have been issued indicating that there may be some continued interest in this area (COGCC, web site 2001).