Water Produced With Coal Bed Methane
Water Produced with Coal-Bed Methane
Introduction
Table 1. Water production in some major coal-bed-methane-producing
basins.
Natural gas produced from coal beds (coal-bed methane, CBM)
[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
accounts for about 7.5 percent of the total natural gas production in the
5/00; data for Powder River Basin from Wyoming Oil and Gas Commission as of 5/00;
United States. Along with this gas, water is also brought to the surface.
data for Raton and San Juan Basins from Colorado and New Mexico Oil and Gas
The amount of water produced from most CBM wells is relatively high
Commissions as of 2/00; data for Uinta Basin from Utah Division of Oil and Gas as of
compared to conventional natural gas wells because coal beds contain
6/00]
many fractures and pores that can contain and transmit large volumes
Avg. water
Water/gas ratio
Primary
of water. In some areas, coal beds may function as regional or local
Basin
State
No. of
production
(Bbl/MCF)
disposal
aquifers and important sources for ground water. The water in coal
wells
(Bbl/day/well)
method
beds contributes to pressure in the reservoir that keeps methane gas
Black
Surface
adsorbed to the surface of the coal. This water must be removed by
Warrior Ala.
2,917
58
0.55
disch.
pumping in order to lower the pressure in the reservoir and stimulate
Powder
Wyo.,
Surface
desorption of methane from the coal (fi g. 1). Over time, volumes of
River
Mont.
2,737
400
2.75
disch.
pumped water typically decrease and the production of gas increases
Raton Colo.
459
266
1.34 Injection
as coal beds near the well bore are dewatered.
San
Colo.,
The need to decrease CO
Juan
N. Mex.
3,089
25
0.031
Injection
2 emissions favors the increased use
of natural gas as an alternative to coal. The contribution of CBM
Uinta Utah
393
215
0.42 Injection
to total natural gas production in the United States is expected to
increase in the foreseeable future (Nelson, 1999). Estimates of the
ing of water data. Volume data for produced water from specifi c
amount of recoverable CBM have increased from about 90 trillion
coal beds has the potential to provide information on exploration and
cubic feet (TCF) 10 years ago to about 141 TCF, spurred by advances
production of CBM. Compositional data is commonly limited to the
in technology, exploration, and production (Nelson, 1999). As the
major dissolved ion species in water (cations and anions), whereas
number of CBM wells increases, the amount of water produced will
information on trace metals and isotopic composition is sparse.
also increase. Reliable data on the volume and composition of associ-
Generally, dissolved ions in water coproduced with CBM contain
ated water will be needed so that States and communities can make
mainly sodium (Na), bicarbonate (HCO3), and chloride (Cl). The com-
informed decisions on CBM development. Most data on CBM waters
position is controlled in great part by the association of the waters with
have been gathered at two historically large production areas, the
a gas phase containing varying amounts of carbon dioxide (CO2) and
San Juan Basin in Colorado and New Mexico (sparse data) and the
methane. The bicarbonate component potentially limits the amount
Black Warrior Basin in Alabama (extensive data). Rapid development
of calcium (Ca) and magnesium (Mg) through the precipitation of
in basins with limited data on CBM waters—i.e., the Powder River
carbonate minerals. CBM waters are relatively low in sulfate (SO4)
Basin in Wyoming and Montana—is currently a concern of produc-
because the chemical conditions in coal beds favor the conversion of
ers; land owners; Federal, State, and local agencies; coal mining
SO4 to sulfi de. The sulfi de is removed as a gas or as a precipitate. The
companies; and Native Americans.
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
Volumes and Compositions of
and within basins. For comparison, the recommended TDS limit for
CBM Water
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
As shown in table 1, the amount of water produced, as well as
the depth of the coal beds, the composition of the rocks surrounding
the ratio of water to gas, varies widely among basins with CBM pro-
the coal beds, the amount of time the rock and water react, and the
duction. Causes of variations include the duration of CBM production
origin of the water entering the coal beds. Trace-element concentra-
in the basin, original
tions in CBM water are commonly low (<1 mg/L) as are volatile
depositional environ-
organic compounds (Gas Research Institute, 1995; Rice, 2000). In
Pump
Water to
Gas to
ment, depth of burial,
general, most CBM water is of better quality than waters produced
separator or
pipeline
discharge
and type of coal. Rel-
from conventional oil and gas wells.
atively recent
regulations concern-
Fate of CBM Water
ing disposal and with-
drawal of produced
Water coproduced with methane is not reinjected into the pro-
water have led to
ducing formation to enhance recovery as it is in many oil fi elds.
more accurate report-
Instead, it must be disposed of or used for benefi cial purpose:
Reuse
Stock ponds/
Water
Figure 1. Simplifi ed
Wetlands
irrigation
supplies
illustration of a coal-bed
CBM water
Treatment
methane production
Surface
Surface
Disposal
Injection
well.
discharge
ponding
U.S. Department of the Interior
USGS Fact Sheet FS-156-00
Printed on recycled paper
U.S. Geological Survey
November 2000
The choice depends in large part on the composition of the
Figure 2. USGS chemist prepares to
water. Important composition information should include TDS (often
sample water from the wellhead of a coal-
equated to the amount of “salt” a water contains), pH, concentrations
bed methane well. Wellhead sampling and
of dissolved metals and radium, and the type and amounts of dis-
on-site sample preservation and analysis
solved organic constituents. If, with minor to no treatment, the water
are critical to obtaining good quality com-
positional and isotopic data. Many parame-
is of suffi cient quality, it may be used with caution to supplement
ters, such as pH, alkalinity, and trace-metal
area water supplies. This water must meet requirements under several
content, change rapidly once the water is
Federal and State regulations, including the Clean Water Act, the Safe
removed from the well.
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
methane desorption, and water com-
by injection into a compatible subsurface formation or by surface
position and isotopic values. Research-
discharge. Disposal of CBM water is also regulated by Federal and
ers from the USGS, Bureau of Land
State agencies and must meet criteria for each type of disposal. For
Management, Bureau of Indian Affairs,
example, subsurface injection requires compatibility studies of the
State agencies, and private companies
proposed injection formation and the water that is injected, whereas
are cooperating in an effort to provide a better understanding of CBM
discharge to surface streams must meet daily effl uent limits on con-
resources and associated water.
stituents such as chlorides along with other criteria. For any CBM
CBM water studies include sampling wells throughout a fi eld as
fi eld, the cost of handling coproduced water varies from a few cents
well as analyzing the volumes of water that are produced. Analyses
per barrel to more than a dollar per barrel and can add signifi cantly
include major, minor, and trace constituents, including arsenic (As),
to the cost of gas production. In some areas, the volumes of water
selenium (Se), copper (Cu), cadmium (Cd), lead (Pb), molybdenum
produced and the cost of handling may prohibit development of the
(Mo), chromium (Cr), mercury (Hg), and zinc (Zn) (fi g. 3). The major
resource.
anions (Cl–, SO 2–
–
4
, and HCO3 ) are measured as well as selected
other constituents, such as ammonia and total organic carbon. Isotopic
USGS Studies of CBM-Produced Water
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 U.S. Geological Survey (USGS) has ongoing studies
the compositional evolution of the water. Volumes of water produced
designed to provide information on the composition and volumes of
from a CBM fi eld are analyzed to determine trends in production that
CBM water in some of the most active areas of production in the
may be related to reservoir parameters such as permeability. In some
United States. Data obtained on CBM waters provides information on
areas of CBM development, USGS Water Resources District Offi ces
the heterogeneity of the CBM reservoir, the potential fl ow paths in
are cooperating with State and Federal agencies to perform targeted
the reservoir, the source and evolution of the water, and the quality
studies such as measuring concentrations of selenium in wetlands and
of the water prior to disposal or reuse. The USGS Energy Resources
dating waters.
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
References Cited
hydrology as well as reservoir-specifi c studies such as coal fracture
orientation, coal composition, gas composition and isotopic values,
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
Average Water Composition
potential of coalbed methane resources, in Gas TIPS: Gas Research Insti-
Uinta Basin (Ferron CBM, Utah) 1
tute, v. 5, no. 2, p. 4–11.
mg/L
Field
TDS
Cl
HCO3
Br / Cl
Rice, C.A., 1999, Waters co-produced with coalbed methane from the Ferron
Sandstone in east-central Utah: Chemical and isotopic composition, vol-
Buzzard
11000
2300
8500
0.0063
Bench
umes, and impacts of disposal: GSA Abstracts with Programs, v. 31, p. A385.
Drunkards
8900
2500
5500
0.0032
Rice, C.A., Ellis, M.S., and Bullock, J.H., Jr., 2000, Water co-produced with
Wash
coalbed methane in the Powder River Basin, Wyoming: Preliminary compo-
Helper State
26000
14000
5200
0.0013
sitional data: U.S. Geological Survey Open-File Report 00-372, 20 p.
Powder River Basin (Wyoming) 2
µg/L
µg/L
CBM
DWS
CBM
DWS
For More Information Please Contact
Arsenic
<3
50
Manganese
32
50
Barium
620
2000
Mercury
<0.3
2
Cynthia A. Rice
Vito Nuccio
U.S. Geological Survey
U.S. Geological Survey
Chromium
<2
100
Selenium
<2
50
Box 25046, Mail Stop 973
Box 25046, Mail Stop 939
Denver Federal Center
Denver Federal Center
Denver, CO 80225
Denver, CO 80225
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
(303) 236-1989
(303) 236-1654
dissolved solids; DWS, drinking water standards. 1, Rice (1999); 2, Rice (2000).
e-mail: crice@usgs.gov
e-mail: vnuccio@usgs.gov
