Water co-produced with coalbed methane in the Powder River Basin, Wyoming: Preliminary compositional data

Abstract

Production of water and natural gas from coal beds (coalbed methane, CBM) has increased dramatically over the past ten years and the gas currently accounts for about 6% of the total produced in the United States. The Powder River Basin (PRB) in Wyoming and Montana (Fig. 1) has emerged as one of the most active new areas of CBM production since 1997. Gas and water are being produced from thick coals in the Paleocene age Fort Union Formation primarily in the eastern part of the basin, although development is expanding to the northwest in the basin at the time of this report. The number of producing wells has increased from 270 in March, 1997 to 2,469 as of March, 2000 (Wyoming Oil and Gas Conservation Commission (WOGCC)). CBM production in the same period has increased from 34,529 thousand cubic feet per day (mcf7day) to over 333,000 mcf/day (WOGCC, 2000). Estimates from State and federal officials and industry representatives of the total number of wells expected in the basin over the next 20-30 years vary from 15,000-70,000. Water is also brought to the surface during production of coalbed methane. The water in coal beds contributes to pressure in the coal beds that keeps methane gas adsorbed to the coal. During production, this water is pumped to the ground surface to lower the pressure in the reservoir and stimulate desorption of methane from the coal. As with gas production, water production in the PRB has also increased in the three-year period between 1997 and 2000 from about 130,000 barrels per day to over 1.28 million barrels per day (WOGCC, 2000), a tenfold increase. As the number of CBM wells increases, the amount of water produced will also increase. Water production from a CBM well typically declines over the life of the well, and declining water production is anticipated and has been observed in CBM wells that have produced for several years. Decline in water production in developing areas of the basin and the basin as a whole is not expected to occur until most of the CBM wells have been developed and produced for a number of years. Reliable data on the composition of the water produced from the CBM wells are needed so that State and federal land use managers can make informed decisions on handling, disposal, and possible beneficial use of water produced with CBM. Previous studies of water associated with coal beds in the PRB have focused on small areas near surface coal mines (Drever and others, 1977; Larson, 1988). Composition data on groundwater in the Fort Union Formation presented previously (Larson and Daddow, 1984) and other data acquired by the State of Wyoming Department of Environmental Quality through the discharge permit process are not coal bed specific. The data may represent co-mingled water from multiple coal beds and/or surface water or water from strata in the Fort Union Formation distinctly different from water produced from coal bed methane wells. Compositional data for CBM water can provide information on the heterogeneity of the CBM reservoirs, the potential flow paths in the Fo...

Passive remediation of coalbed natural gas co-produced water using zeolite

“…High SAR values can also reduce the absorption of water by vegetation (Warrance et al, 2001). Researchers have reported that water from CBNG wells in the PRB is mostly dominated by Na þ and bicarbonate (HCO 3 -) ions with pH values ranging from 6.8 to 9.2, EC ranging from 0.4 to 5.0 dS/m, and SAR ranging from 5.0 to 70.0 (mol/m 3 ) 1/2 (Rice et al, 2000;Ganjegunte et al, 2005;Jackson and Reddy, 2007;Johnston et al, 2008;Vance et al, 2008). Generally, SAR values between w10 and 18 (mol/m 3 ) 1/2 are considered a medium hazard, SAR values between 18 and 26 (mol/m 3 ) 1/2 are a high hazard, and SAR values above 26 (mol/m 3 ) 1/2 are deemed a very high hazard (Richards, 1954;Fetter, 2001).…”

Water produced with coal-bed methane

“…The TDS of the water is dependent upon the depth of the coal beds, the composition of the rocks surrounding the coal beds, the amount of time the rock and water react, and the origin of the water entering the coal beds. Trace-element concentrations in CBM water are commonly low (<1 mg/L) as are volatile organic compounds (Gas Research Institute, 1995;Rice, 2000). In general, most CBM water is of better quality than waters produced from conventional oil and gas wells.…”

Research and Development Concerning Coalbed Natural Gas

“…Much work has been done to determine the characteristics of PRB CBM waters (Rice et al 2000;McBeth et al 2003, Patz et al 2004, Patz et al 2006). The conclusion from research has shown that CBM water constituent concentrations vary from watershed to watershed in the PRB (McBeth et al 2003).…”