Introduction

Natural gas produced from coal beds (coal-bed methane, CBM) 

accounts for about 7.5 percent of the total natural gas production in the 

United States. Along with this gas, water is also brought to the surface. 

The amount of water produced from most CBM wells is relatively high 

compared to conventional natural gas wells because coal beds contain 

many fractures and pores that can contain and transmit large volumes 

of water. In some areas, coal beds may function as regional or local 

aquifers and important sources for ground water. The water in coal 

beds contributes to pressure in the reservoir that keeps methane gas 

adsorbed to the surface of the coal. This water must be removed by 

pumping in order to lower the pressure in the reservoir and stimulate 

desorption of methane from the coal (fi g. 1). Over time, volumes of 

pumped water typically decrease and the production of gas increases 

as coal beds near the well bore are dewatered.

The need to decrease CO2 emissions favors the increased use 

of natural gas as an alternative to coal. The contribution of CBM 

to total natural gas production in the United States is expected to 

increase in the foreseeable future (Nelson, 1999). Estimates of the 

amount of recoverable CBM have increased from about 90 trillion 

cubic feet (TCF) 10 years ago to about 141 TCF, spurred by advances 

in technology, exploration, and production (Nelson, 1999). As the 

number of CBM wells increases, the amount of water produced will 

also increase. Reliable data on the volume and composition of associated water will be needed so that States and communities can make 

informed decisions on CBM development. Most data on CBM waters 

have been gathered at two historically large production areas, the 

San Juan Basin in Colorado and New Mexico (sparse data) and the 

Black Warrior Basin in Alabama (extensive data). Rapid development 

in basins with limited data on CBM waters—i.e., the Powder River 

Basin in Wyoming and Montana—is currently a concern of producers; land owners; Federal, State, and local agencies; coal mining 

companies; and Native Americans.

Volumes and Compositions of 

CBM Water

As shown in table 1, the amount of water produced, as well as 

the ratio of water to gas, varies widely among basins with CBM production. Causes of variations include the duration of CBM production 

ing of water data. Volume data for produced water from specifi c 

coal beds has the potential to provide information on exploration and 

production of CBM. Compositional data is commonly limited to the 

major dissolved ion species in water (cations and anions), whereas 

information on trace metals and isotopic composition is sparse.

Generally, dissolved ions in water coproduced with CBM contain 

mainly sodium (Na), bicarbonate (HCO3), and chloride (Cl). The composition is controlled in great part by the association of the waters with 

a gas phase containing varying amounts of carbon dioxide (CO2) and 

methane. The bicarbonate component potentially limits the amount 

of calcium (Ca) and magnesium (Mg) through the precipitation of 

carbonate minerals. CBM waters are relatively low in sulfate (SO4) 

because the chemical conditions in coal beds favor the conversion of 

SO4 to sulfi de. The sulfi de is removed as a gas or as a precipitate. The 

total dissolved solids (TDS) of CBM water ranges from fresh (200 

mg/L or parts per million) to saline (170,000 mg/L) and varies among 

and within basins. For comparison, the recommended TDS limit for 

potable water is 500 mg/L, and for benefi cial use such as stock ponds 

or irrigation, the limit is 1,000–2,000 mg/L. Average seawater has a 

TDS of about 35,000 mg/L. 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.

Water Produced with Coal-Bed Methane

Figure 1. Simplifi ed 

illustration of a coal-bed 

methane production 

well.

in the basin, original 

depositional environment, depth of burial, 

and type of coal. Relatively recent 

regulations concerning disposal and withdrawal of produced 

water have led to 

more accurate reportCBM water

Disposal

Reuse

Surface

discharge

Surface 

ponding Injection

Treatment

Stock ponds/

irrigation Wetlands Watersupplies

Fate of CBM Water

Water coproduced with methane is not reinjected into the producing formation to enhance recovery as it is in many oil fi elds. 

Instead, it must be disposed of or used for benefi cial purpose:

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-156-00

November 2000 Printed on recycled paper

Gas to

pipeline

Water to

separator or

discharge

Pump

Table 1. Water production in some major coal-bed-methane-producing 

basins. 

[Bbl, barrel (42 gallons); MCF, thousand cubic feet; No., Number; Avg., Average; disch., 

discharge. Data for Black Warrior Basin from Alabama State Oil and Gas Board as of 

5/00; data for Powder River Basin from Wyoming Oil and Gas Commission as of 5/00; 

data for Raton and San Juan Basins from Colorado and New Mexico Oil and Gas 

Commissions as of 2/00; data for Uinta Basin from Utah Division of Oil and Gas as of 

6/00] 

Basin State No. of 

wells 

Avg. water 

production 

(Bbl/day/well) 

Water/gas ratio 

(Bbl/MCF) 

Primary 

disposal 

method 

Black 

 Warrior Ala. 2,917 58 0.55 

Surface 

 disch. 

Powder 

 River 

Wyo., 

Mont. 2,737 400 2.75 

Surface 

 disch. 

Raton Colo. 459 266 1.34 Injection 

San 

 Juan 

Colo., 

N. Mex. 3,089 25 0.031 Injection 

Uinta Utah 393 215 0.42 Injection 
The choice depends in large part on the composition of the 

water. Important composition information should include TDS (often 

equated to the amount of “salt” a water contains), pH, concentrations 

of dissolved metals and radium, and the type and amounts of dissolved organic constituents. If, with minor to no treatment, the water 

is of suffi cient quality, it may be used with caution to supplement 

area water supplies. This water must meet requirements under several 

Federal and State regulations, including the Clean Water Act, the Safe 

Drinking Water Act, and the Resource Conservation and Recovery 

Act. If the water does not meet Federal and State standards for reuse, 

or if the cost of treatment is excessive, the water is disposed of 

by injection into a compatible subsurface formation or by surface 

discharge. Disposal of CBM water is also regulated by Federal and 

State agencies and must meet criteria for each type of disposal. For 

example, subsurface injection requires compatibility studies of the 

proposed injection formation and the water that is injected, whereas 

discharge to surface streams must meet daily effl uent limits on constituents such as chlorides along with other criteria. For any CBM 

fi eld, the cost of handling coproduced water varies from a few cents 

per barrel to more than a dollar per barrel and can add signifi cantly 

to the cost of gas production. In some areas, the volumes of water 

produced and the cost of handling may prohibit development of the 

resource.

USGS Studies of CBM-Produced Water

The U.S. Geological Survey (USGS) has ongoing studies 

designed to provide information on the composition and volumes of 

CBM water in some of the most active areas of production in the 

United States. Data obtained on CBM waters provides information on 

the heterogeneity of the CBM reservoir, the potential fl ow paths in 

the reservoir, the source and evolution of the water, and the quality 

of the water prior to disposal or reuse. The USGS Energy Resources 

Team is conducting multidisciplinary studies in the Uinta and Powder 

River Basins that include sampling waters coproduced with CBM 

(fi g. 2). These studies combine investigations of regional geology and 

hydrology as well as reservoir-specifi c studies such as coal fracture 

orientation, coal composition, gas composition and isotopic values, 

Cynthia A. Rice

U.S. Geological Survey

Box 25046, Mail Stop 973

Denver Federal Center

Denver, CO 80225

(303) 236-1989

e-mail: crice@usgs.gov

Vito Nuccio

U.S. Geological Survey

Box 25046, Mail Stop 939

Denver Federal Center

Denver, CO 80225

(303) 236-1654

e-mail: vnuccio@usgs.gov

For More Information Please Contact

Figure 2. USGS chemist prepares to 

sample water from the wellhead of a coalbed methane well. Wellhead sampling and 

on-site sample preservation and analysis 

are critical to obtaining good quality compositional and isotopic data. Many parameters, such as pH, alkalinity, and trace-metal 

content, change rapidly once the water is 

removed from the well.

References Cited

Gas Research Institute, 1995, Atlas of gas-related produced water for 1990: Gas 

Research Institute Topical Report GRI-95/0016, 88 p.

Nelson, C.R., 1999, Changing perceptions regarding the size and production 

potential of coalbed methane resources, in Gas TIPS: Gas Research Institute, v. 5, no. 2, p. 4–11.

Rice, C.A., 1999, Waters co-produced with coalbed methane from the Ferron 

Sandstone in east-central Utah: Chemical and isotopic composition, volumes, and impacts of disposal: GSA Abstracts with Programs, v. 31, p. A385.

Rice, C.A., Ellis, M.S., and Bullock, J.H., Jr., 2000, Water co-produced with 

coalbed methane in the Powder River Basin, Wyoming: Preliminary compositional data: U.S. Geological Survey Open-File Report 00-372, 20 p.

Average Water Composition 

Buzzard

 Bench

Uinta Basin (Ferron CBM, Utah) 1

Powder River Basin (Wyoming) 2

Drunkards

 Wash

Helper State

Field TDS

Arsenic

CBM

<3 50

620 2000

<2 100 50 <2

32 50

μg/L μg/L

mg/L

DWS CBM DWS

Barium

Chromium Selenium

Manganese

Mercury <0.3 2

Cl HCO3 Br / Cl

11000

8900

26000

2300 8500

2500 5500

14000 5200 0.0013

0.0032

0.0063

Figure 3. Concentrations of selected components in CBM water from three 

fi elds in the Ferron CBM area, Utah, and from 47 wells in Wyoming. TDS, total 

dissolved solids; DWS, drinking water standards. 1, Rice (1999); 2, Rice (2000).

methane desorption, and water composition and isotopic values. Researchers from the USGS, Bureau of Land 

Management, Bureau of Indian Affairs, 

State agencies, and private companies 

are cooperating in an effort to provide a better understanding of CBM 

resources and associated water.

CBM water studies include sampling wells throughout a fi eld as 

well as analyzing the volumes of water that are produced. Analyses 

include major, minor, and trace constituents, including arsenic (As), 

selenium (Se), copper (Cu), cadmium (Cd), lead (Pb), molybdenum 

(Mo), chromium (Cr), mercury (Hg), and zinc (Zn) (fi g. 3). The major 

anions (Cl–, SO4

2–, and HCO3–) are measured as well as selected 

other constituents, such as ammonia and total organic carbon. Isotopic 

analyses of the samples for deuterium, oxygen, and carbon provide 

data to help determine the origin of the water and its solutes as well as 

the compositional evolution of the water. Volumes of water produced 

from a CBM fi eld are analyzed to determine trends in production that 

may be related to reservoir parameters such as permeability. In some 

areas of CBM development, USGS Water Resources District Offi ces 

are cooperating with State and Federal agencies to perform targeted 

studies such as measuring concentrations of selenium in wetlands and 

dating waters.