U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5109

Prepared in Cooperation with the

Colorado Water Conservation Board

A Preliminary Evaluation of Vertical Separation between 

Production Intervals of Coalbed-Methane Wells and 

Water-Supply Wells in the Raton Basin, Huerfano and 

Las Animas Counties, Colorado, 1999–2004
A Preliminary Evaluation of Vertical 

Separation between Production Intervals 

of Coalbed-Methane Wells and WaterSupply Wells in the Raton Basin, Huerfano 

and Las Animas Counties, Colorado, 

1999–2004

By Kenneth R. Watts

Prepared in Cooperation with the 

Colorado Water Conservation Board

Scientific Investigations Report 2006–5109

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

P. Lynn Scarlett, Acting Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

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iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Hydrogeologic Setting .........................................................................................................................2

Depths of Water-Supply Wells and Production Intervals of Coalbed-Methane Wells.............2

Ground-Water Pumping.......................................................................................................................4

Vertical Separation between Production Intervals of Coalbed-Methane Wells and 

Water-Supply Wells .........................................................................................................................4

Potential Changes in Water Levels Resulting from Coalbed-Methane Production ..................4

Hypothetical Effects of Coalbed-Methane Production on Nearby Water-Supply Wells..........5

Estimated Vertical Separation between Production Intervals of Coalbed-Methane

and Water-Supply Wells ........................................................................................................5

Summary..........................................................................................................................................................5

References Cited............................................................................................................................................8

Figures

1. Map showing location of the study area..................................................................................2

2. Graph showing annual production of coalbed methane and ground 

water in the Raton Basin, Huerfano and Las Animas Counties, 

Colorado, 1999–2004.....................................................................................................................2

3. Generalized geologic map of the Raton Basin, Colorado and New Mexico. .....................3

4. Simplified schematic diagram showing hypothetical hydraulic connections 

between production zones of a coalbed-methane well and nearby 

water-supply wells. ......................................................................................................................6

5. Estimated vertical separation between production intervals of 

coalbed-methane and water-supply wells in the Raton Basin, 

Huerfano and Las Animas Counties, Colorado, 1999–2004....................................................7
iv

Conversion Factors and Vertical Datum

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 square hectometer (hm2) 

acre 0.004047 square kilometer (km2)

section (640 acres or 1 square mile) 259.0 square hectometer (hm2) 

square mile (mi2) 2.590 square kilometer (km2) 

Volume

barrel (bbl), (petroleum, 

1 barrel=42 gal)

0.1590 cubic meter (m3) 

gallon (gal) 0.003785 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Flow rate

gallon per minute (gal/min) 0.06309 liter per second (L/s)

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

gallon per year (gal/yr) 0.003785 cubic meter per year (m3/yr)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Pressure1

pound per square inch (lb/in2) 6.895 kilopascal (kPa) 

Energy (natural gas) 2

British thermal unit (Btu) 1,054.18 joules (J)

cubic foot (ft3) 1,082,643 joules (J), (approximate)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

1

The pressure at the bottom of a 1-foot-high column of water, at 4oC, is 0.433515 pounds per square inch 

(The Chemical Rubber Company, 1973).

2

The energy in 1 cubic foot of natural gas is approximately equivalent to 1,027 British thermal units 

(American Gas Association, 2006).
Abstract

The Raton Basin in southern Colorado and northern 

New Mexico is undergoing increased development of its 

coalbed-methane resources. Annual production of methane 

from coalbeds in the Raton Basin in Huerfano and Las Animas 

Counties, Colorado, increased from about 28,000,000 thousand cubic feet from 478 wells to about 80,000,000 thousand 

cubic feet from 1,543 wells, during 1999–2004. Annual 

ground-water withdrawals for coalbed-methane production 

increased from about 1.45 billion gallons from 480 wells to 

about 3.64 billion gallons from 1,568 wells, during 1999–

2004. Where the coalbeds are deeply buried near the center 

of the Raton Basin, water pressure may be reduced as much 

as 250 to 300 pounds per square inch to produce the methane 

from the coalbeds, which is equivalent to a 577- to 692-foot 

lowering of water level. In 2001, the U.S. Geological Survey, 

in cooperation with the Colorado Water Conservation Board, 

began an evaluation of the potential effects of coalbedmethane production on the availability and sustainability of 

ground-water resources.

In 2003, there were an estimated 1,370 water-supply 

wells in the Raton Basin in Colorado, and about 90 percent 

of these water-supply wells were less than 450 feet deep. The 

tops of the production (perforated) interval of 90 percent of 

the coalbed-methane wells in the Raton Basin (for which data 

were available) are deeper than about 675 feet. The potential for interference of coalbed-methane wells with nearby 

water-supply wells likely is limited because in most areas their 

respective production intervals are separated by more than a 

hundred to a few thousand feet of rock. The estimated vertical 

separation between production intervals of coalbed-methane 

and water-supply wells is less than 100 feet in an area about 

1 to 6 miles west and southwest of Trinidad Lake and a few 

other isolated areas. It is assumed that in areas with less than 

100 feet of vertical separation, production by coalbed-methane 

wells has a greater potential for interfering with nearby watersupply wells. More detailed geologic and hydrologic information is needed in these areas to quantify the potential effects of 

coalbed-methane production on water levels and the availability and sustainability of ground-water resources.

Introduction

The Rocky Mountain region contains several sedimentary 

provinces with extensive coal deposits and significant accumulations of coalbed gas (Schenk and others, 2001). Production of coalbed gas, which is referred to as “coalbed methane” 

(CBM), carries with it some technological and environmental 

difficulties and costs. Unlike conventional oil or gas reservoirs, 

water permeates coalbeds, and water pressure compresses 

and traps gas within the coal (Schenk and others, 2001). To 

produce the gas (methane) from coal, water must be drawn off 

first to lower the fluid pressure so methane can flow out of the 

coal and to the well bore (Nuccio, 2000). Reduction of fluid 

pressure for CBM production can affect the availability and 

sustainability of local ground-water supplies. If water wells are 

completed in coalbeds or coalbeds are hydraulically connected 

with aquifers in which water wells are completed, CBM production may interfere with nearby water-supply wells.

The Raton Basin in southern Colorado and northern 

New Mexico (fig. 1) is undergoing increased development of 

its coalbed-methane resources. Production of methane from 

coalbeds in the Raton Basin in Huerfano and Las Animas 

Counties, Colorado (fig. 1), increased substantially during 

1999–2004. About 28,000,000 thousand cubic feet (Mcf) of 

CBM was produced from 478 wells during 1999 and about 

80,000,000 Mcf was produced from 1,543 wells during 2004 

in the Raton Basin in Colorado (fig. 2) (Colorado Oil and Gas 

Conservation Commission, 2005). Ground-water withdrawals by CBM wells in Huerfano and Las Animas Counties 

increased from about 1.45 billion gallons from 480 wells, 

during 1999, to about 3.64 billion gallons from 1,568 wells, 

during 2004 (fig. 2) (Colorado Oil and Gas Conservation 

Commission, 2005). Because of the increased withdrawals of ground water for CBM production, water-well owners 

A Preliminary Evaluation of Vertical Separation between 

Production Intervals of Coalbed-Methane Wells and 

Water-Supply Wells in the Raton Basin, Huerfano and Las 

Animas Counties, Colorado, 1999–2004

By Kenneth R. Watts
and resource managers are concerned that the reductions 

of fluid pressure in the coalbeds could affect nearby watersupply wells and the availability and sustainability of local 

ground-water supplies. In 2001, the U.S. Geological Survey, 

in cooperation with the Colorado Water Conservation Board, 

began a preliminary evaluation of the potential effects of CBM 

production on the availability and sustainability of groundwater resources.

Purpose and Scope

This report presents results from a preliminary evaluation of the vertical separation between production intervals of 

CBM wells and nearby water-supply wells in the Raton Basin, 

in Huerfano and Las Animas Counties, Colorado. Data for 

more than 1,600 oil and gas wells in Huerfano and Las 

Animas Counties were retrieved from the database of the 

Colorado Oil and Gas Conservation Commission at http://

www.oil-gas.state.co.us. Data for more than 2,000 water 

wells in Huerfano and Las Animas Counties, Colorado, were 

retrieved from the Colorado Division of Water Resources 

at http://water.state.co.us (Colorado Division of Water 

Resources, 2003). [Note: Well data can no longer be retrieved 

from the Colorado Division of Water Resources Web site.]

Hydrogeologic Setting

The Raton Basin is an asymmetrical trough in southern 

Colorado and northern New Mexico that contains several thousand feet of coal-bearing clastic sedimentary rocks, primarily 

sandstone, siltstone, shale, and conglomerate (fig. 3, from 

Flores and Bader, 1999). Coalbeds in the Raton and Vermejo 

Formations are the primary targets for CBM development in 

the Raton Basin. The Raton and Vermejo Formations and the 

Trinidad Sandstone, which underlies the Vermejo Formation, 

also are sources of ground water for many water-supply wells 

in the Raton Basin (Geldon, 1989). Most ground-water flow 

in the Raton-Vermejo-Trinidad aquifer (Geldon, 1989) occurs 

in sandstones and thick coal seams, but fractured siltstone 

and shale also transmit water. Regional ground-water flow in 

the Raton-Vermejo-Trinidad aquifer is from west to east but 

is deflected towards stream valleys (Abbott and others, 1983; 

Geldon, 1989). Locally, igneous intrusions (dikes) may form 

barriers to ground-water flow (Geldon, 1989). Flow paths 

within the Raton-Vermejo-Trinidad aquifer and overlying 

aquifers are complex because of the effects of geology and 

topography.

Depths of Water-Supply Wells and Production 

Intervals of Coalbed-Methane Wells

In 2003, there were an estimated 1,370 water-supply 

wells in the Raton Basin in Colorado, and about 90 percent 

of these water-supply wells were less than 450 feet deep 

(Topper and others, 2003). Because the tops of the production (perforated) interval of 90 percent of the CBM wells in 

the Raton Basin (for which data were available) are deeper 

than about 675 feet, areas in which production intervals of 

CBM and water-supply wells overlap are limited. Typically, a 

well screen or perforated casing is installed in the production 

interval of a water-supply well and plain casing is installed 

Denver

108o

40o

38o

106o 104o 102o

COLORADO

HUERFANO

LAS ANIMAS

Trinidad

Walsenburg

Study

area

Based from U.S. Geological Survey County Map Series, 1979, 1:50,000

Albers Equal-Area Conic projection

Standard parallels 37o30’N and 40o30’N, central meridian105o30’W

Figure 1. Location of the study area.

0

20

40

60

80

100

ANNUAL METHANE PRODUCTION, 

IN BILLION CUBIC FEET

Methane

Ground water

0

1

2

3

4

5

ANNUAL GROUND-WATER PRODUCTION, 

IN BILLION GALLONS

1999 2000 2001 2002 2003 2004 478 480

1,354 1,364

964

988

1,160

1,184

659

681

1,543

1,568

Figure 2. Annual production of coalbed methane and ground 

water in the Raton Basin, Huerfano and Las Animas Counties, 

Colorado, 1999–2004.

   A Preliminary Evaluation of Vertical Separation between Production Intervals of Coalbed-Methane Wells and WaterSupply Wells in the Raton Basin, Huerfano and Las Animas Counties, Colorado, 1999–2004
}

}

N

0 15 MILES0 15 KILOMETERS

Stonewall

Raton

Sangre de Cristo Mountains

Basin axis

Walsenburg

Apishapa

arch

La As nimas ra hc

i S re ra Gran ed ar hc

Colorado

New Mexico

37o

105o

Colorado

New

Mexico

Raton Basin

Alluvium, slopewash, andlandslide materialBasalt flowsHuerfano FormationMiddle Tertiary intrusivesCuchara FormationPoison Canyon FormationRaton FormationVermejo FormationTrinidad Sandstone andPierre Shale undividedPierre Shale/Niobrara undividedPrecambrian rock undividedRaton Basin boundary

Holocene andQuaternary

TertiaryCretaceous

Modified from Flores and Bader (1999).

Figure 3. Generalized geologic map of the Raton Basin, Colorado and New Mexico.

Introduction   
above the production interval. Except for a mandatory surface 

(sanitary) seal, water-supply wells typically are not cemented 

(grouted) above the production interval, unless another aquifer 

overlies the producing aquifer. A typical CBM well is drilled, 

cased, and cemented through overlying strata and the potential 

production interval (Colorado Oil and Gas Conservation Commission, variously dated). The casing of a CBM well is perforated in selected intervals that contain coal seams, and the coal 

seams may be hydraulically fractured to increase permeability 

of the production interval. The casing and cement are designed 

to prevent hydraulic connection between the perforated and 

nonperforated intervals in the annular space between the borehole and casing of the CBM well.

Ground-Water Pumping

Annual ground-water pumping for domestic, irrigation, 

and municipal supplies in Huerfano and Las Animas Counties was an estimated 1.7 billion gallons in 2000 (Hutson and 

others, 2004), which is equivalent to about 47 percent of 3.64 

billion gallons that was produced by 1,568 CBM wells in the 

Raton Basin during 2004. Generally in Colorado, the annual 

rate of withdrawal for a household well on less than 35 acres 

is limited to 0.33 acre-foot and the limit for a domestic well on 

35 or more acres is 1 acre-foot (Colorado Division of Water 

Resources, 2005). Annual withdrawals of 0.33 and 1 acre-foot 

are equivalent to average pumping rates of about 0.21 and 

0.62 gallon per minute, respectively. During 2004, combined 

production of ground water by 1,568 CBM wells in the Raton 

Basin was about 3.64 billion gallons. The average pumping 

rate for CBM production well in the Raton Basin of Colorado 

during 2004 was about 4.4 gallons per minute [3.64 billion 

gallons per year ÷ (365 days per year * 1,440 minutes per day 

* 1,568 wells) ≈ 4.4 gallons per minute per well].

Typically, as CBM production proceeds, the ratio of produced gas (methane) to water is smallest during initial phases 

of development, when water pressure in the coalbeds is being 

reduced and the volume of ground water produced with gas 

is large. The ratio of gas to water increases with time, as the 

volume of produced gas increases and produced ground water 

decreases, until the gas production decreases as the storage 

is depleted (Kuuskraa and Brandenberg, 1989). Based on the 

available data (fig. 2), it appears that the Raton Basin is still 

in the initial or depressurization phase of development. As 

fluid pressure in the CBM production intervals decreases, the 

cumulative annual withdrawal of ground water by CBM wells 

in the Raton Basin is expected to decrease, unless more CBM 

wells are brought into production.

Ground water produced by CBM wells in the Raton 

Basin generally is not returned to the intervals from which it 

was pumped. There are several methods used for disposal of 

CBM-produced water in the Raton Basin, including injection 

into deeper geologic units, discharge to surface drainages, 

and discharge to lined (evaporation) or unlined (recharge) 

pits (Colorado Oil and Gas Conservation Commission, 2000). 

Some CBM-produced water also is used for dust suppression 

on unpaved roads. CBM-produced water that is discharged at 

the surface or in recharge pits may recharge shallow aquifers. 

CBM production could deplete ground-water storage in the 

coalbeds, unless additional recharge is captured and (or) discharge is intercepted.

Vertical Separation between 

Production Intervals of CoalbedMethane Wells and Water-Supply 

Wells

When fluid (water or gas) pressure in an aquifer (coalbed) is reduced at a CBM well, the flow of fluid will increase 

from areas of greater potential toward the CBM well. The rate 

of flow toward a CBM well and the effects on fluid pressure 

in the area around the well are controlled by the permeability and storage properties of the coal and surrounding rocks, 

the physical properties of the fluid (gas and water), and the 

amount and duration of pressure reduction at the CBM well. 

Because the permeability of stratified sedimentary rocks generally is greater parallel to bedding than across bedding, it is 

assumed that CBM production likely would have the greatest 

potential for interfering with nearby water-supply wells, in 

areas in which there is no or little vertical separation between 

their respective production intervals.

Potential Changes in Water Levels Resulting 

from Coalbed-Methane Production 

In general, the fluid pressure (water level) in the coalbeds is reduced to attain a water level above the top of the 

perforated interval of the CBM production well. Where the 

coalbeds are deeply buried near the center of the Raton Basin, 

fluid pressure may be reduced as much as 250 to 300 pounds 

per square inch. The pressure exerted by a 1-foot-tall column 

of water, at 4oC, is 0.433515 pounds per square inch (The 

Chemical Rubber Company, 1973). Thus, a fluid-pressure 

reduction of 250 to 300 pounds per square inch is equivalent 

to a reduction of water level of approximately 577 to 692 feet. 

Reductions in fluid pressure (water level) in CBM production 

wells that are located nearer the outcrop of the coalbeds likely 

are less than fluid-pressure reductions in wells in areas where 

the coalbeds are deeply buried. Because changes in fluid pressure (water level) in an aquifer are inversely proportional to 

the distance squared from the pumped well (Theis, 1935), the 

largest changes in fluid pressure (water level) will occur in 

the production intervals (coalbeds) near the CBM wells, and 

changes will decrease exponentially away from the production 

      A Preliminary Evaluation of Vertical Separation between Production Intervals of Coalbed-Methane Wells and WaterSupply Wells in the Raton Basin, Huerfano and Las Animas Counties, Colorado, 1999–2004
wells. Because changes in fluid pressure (water level) in an 

aquifer are proportional to the rate and duration of pumping, 

changes will be greatest near the CBM wells that produce the 

most water. Changes of fluid pressure (water level) resulting 

from pumping also are a function of the hydraulic and storage 

properties of the rocks and may be affected by flow barriers (faults and dikes) and leakage from or through overlying 

and underlying rocks. Quantitative estimates of the change in 

fluid pressure (water level) caused by pumping a CBM well 

require detailed knowledge of the production history of the 

well, hydraulic and storage properties of the coalbeds and 

adjacent rocks, and distances to hydraulic boundaries (barriers 

or sources).

Hypothetical Effects of Coalbed-Methane 

Production on Nearby Water-Supply Wells

A simplified schematic diagram (fig. 4) illustrates why 

water levels in some water-supply wells could be affected by 

CBM production while other nearby wells are not affected. 

Pumping by a hypothetical CBM well (fig. 4, well B) might 

not cause water-level declines in (interfere with) a nearby 

water-supply well (fig. 4, well A) if the vertical separation of 

production intervals of a CBM well and a water-supply well 

is large and the intervening rock is unfractured and relatively 

impermeable siltstone and shale. Pumping by a CBM well 

(fig. 4, well B) might interfere with a nearby water-supply 

well if the intervening rock is relatively permeable coal, sandstone, or fractured siltstone and shale (fig. 4, well C) or the 

vertical separation of production intervals is small (fig. 4, well 

D). Pumping by a CBM well (fig. 4, well B) eventually could 

interfere with more distant water-supply wells (fig. 4, wells 

E and F), if the CBM well and the water-supply wells are 

completed in the same interval and pumping by the CBM well 

is large and continues for an extended period. Flow barriers 

(not shown in fig. 4) formed by changes in lithology (facies 

changes), vertical offsets of bedding at faults, or intrusive 

rocks (dikes) also may affect water-level changes in water-supply wells due to pumping CBM wells, depending on the location of the flow barriers relative to the CBM and water-supply 

wells.

Estimated Vertical Separation between 

Production Intervals of Coalbed-Methane and 

Water-Supply Wells

The potential for interference of CBM production wells 

with water-supply wells likely is greatest in areas where the 

CBM wells and water-supply wells are producing from the 

same interval or there is little vertical separation between their 

respective production intervals. The generalized thickness of 

the rock separating the production intervals of CBM wells and 

nearby (within 1 mile) water-supply wells is shown in figure 5. 

The minimum vertical separation (fig. 5) of “0 to 100 feet” is 

an arbitrary limit and does not imply that 100 feet is the vertical separation needed to prevent interference between CBM 

wells and nearby water-supply wells. Figure 5 was created, 

using a geographic information system, by comparing the 

altitudes of the top and bottom of production intervals of CBM 

wells with the altitude of the bottom of water-supply wells. 

Altitudes of the production intervals of CBM wells were calculated from the reported land-surface altitude at and depths 

to the top and bottom of the perforated intervals of CBM wells 

(Colorado Oil and Gas Conservation Commission, 2005). 

About one-third of the CBM wells in the Raton Basin were not 

used in preparation of figure 5 because production intervals 

were not available for these wells. Altitudes of the bottom of 

the water-supply wells were calculated as the altitude of the 

land surface at a well, as estimated from the 1-Arc-second 

National Elevation Dataset (U.S. Geological Survey, 2004), 

minus the depth to the bottom of the well (Colorado Division 

of Water Resources, 2003). [One Arc-second is approximately 

a distance of about 30 meters or 98 feet.] Because local relief 

of the land surface may be several hundred feet in the Raton 

Basin and the location of a water-supply well may be accurate 

only to the nearest 40-acre tract, errors in well location could 

be as large as about 934 feet and could result in large errors in 

the estimated altitude of the land surface.

In most of the Raton Basin in Colorado, the potential 

for interference of CBM wells with nearby water-supply 

wells likely is limited because the production intervals of 

CBM wells and nearby water-supply wells, in most areas, are 

separated by hundreds to a few thousand feet of rock (fig. 5). 

Locally, in an area about 1 to 6 miles west and southwest 

of Trinidad Lake and a few other isolated areas (fig. 5), the 

estimated vertical separation between production intervals 

of CBM and water-supply wells is less than 100 feet. It is 

assumed that in these areas, pumping of CBM wells has a 

greater potential for interfering with nearby water-supply 

wells; however, more detailed geologic and hydrologic information is needed in these areas to estimate the potential effects 

of CBM production on water levels.

Additional data that are needed to better understand the 

effects of CBM development on the availability and sustainability of ground-water resources in the Raton Basin of 

Colorado include better definitions of the hydrostratigraphic 

framework (three-dimensional geometry) and the hydraulic 

and storage properties of the aquifers and confining units, the 

production characteristics and perforated intervals of CBM 

and water-supply wells, and the monitoring of fluid pressures 

and water levels in CBM and water-supply wells.

Vertical Separation between Production Intervals of Coalbed-Methane Wells and Water-Supply Wells 
F

A

B

C

D

P

E

roduction interval

Sandstone, siltstone, and shaleSandstone and conglomerateCoalShaleWater-well casingGas-well casing

Figure 4. Hypothetical hydraulic connections between production zones of a coalbed-methane well and nearby water-supply wells.

 A Preliminary Evaluation of Vertical Separation between Production Intervals of Coalbed-Methane Wells and WaterSupply Wells in the Raton Basin, Huerfano and Las Animas Counties, Colorado, 1999–2004
HUERFANO

LAS ANIMAS

25

M A X W E L L G R A N T

Trinidad

Walsenburg

Aguilar

160

160

160

25

350

87

10

85

La Veta

Cokedale

Starkville

69

T.

27

S.

T.

28

S.

T.

29

S.

T.

30

S.

T.

31

S.

T.

32

S.

T.

33

S.

T.

34

S.

T.

35

S.

25

R. 69 W. R. 68 W. R. 67 W. R. 66 W. R. 65 W. R. 64 W. R. 63 W. R. 62 W. R. 61 W.

25

160

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

12

37o

37o15’

105o 104o45’ 104o30’ 104o15’

Estimated vertical separation

between production intervals

of coalbed-methane and 

water-supply wells (feet)

Less than or equal to 100

More than 100 to 250

More than 250 to 750

More than 750 to 2,000

More than 2,000 to 5,800

Raton Basin boundary

Coalbed-methane well

Water-supply well

Albers Equal Area Projection.

North American Datum of 1983.

Trinidad Lake

Figure 5. Estimated vertical separation between production intervals of coalbed-methane and water-supply wells in the Raton Basin, 

Huerfano and Las Animas Counties, Colorado, 1999–2004.

Vertical Separation between Production Intervals of Coalbed-Methane Wells and Water-Supply Wells 
Summary

Reduction of fluid pressure for coalbed-methane production can affect the availability and sustainability of local 

ground-water supplies. Coalbed-methane production has a 

greater potential for interference with nearby water-supply 

wells, if the water wells are completed in the coalbeds or in 

aquifers that are hydraulically connected with the coalbeds. 

Production of coalbed methane increased substantially during 

1999–2004 in the Raton Basin in Huerfano and Las Animas 

Counties, Colorado. About 28,000,000 thousand cubic feet of 

coalbed methane was produced from 478 wells during 1999 

and about 80,000,000 thousand cubic feet was produced­ from

1,543 wells during 2004 in the Raton Basin in Colorado. 

Ground-water withdrawals by coalbed-methane wells in 

Huerfano and Las Animas Counties increased from about 

1.45 billion gallons from 480 wells, during 1999, to about 

3.64 billion gallons from 1,568 wells, during 2004. Where the 

coalbeds are deeply buried near the center of the Raton Basin, 

fluid pressure may be reduced as much as 250 to 300 pounds 

per square inch, which is equivalent to a reduction of water 

levels of approximately 577 to 692 feet. Water-well owners 

and resource managers are concerned that the reductions of 

fluid pressure in the coalbeds could affect nearby water-supply 

wells and the availability and sustainability of local groundwater supplies. In 2001, the U.S. Geological Survey, in cooperation with the Colorado Water Conservation Board, began 

an evaluation of the potential effects of coalbed-methane 

production on the availability and sustainability of groundwater resources. This report presents preliminary results from 

an evaluation of the vertical separation between production 

intervals of coalbed-methane wells and nearby water-supply 

wells in the Raton Basin of Colorado.

Geographic information system software was used to 

estimate the vertical separation between production intervals 

of coalbed-methane wells and nearby water-supply wells, 

based on water-well construction data from the Colorado 

Division of Water Resources and gas-well construction data 

from the Colorado Oil and Gas Conservation Commission. 

In 2003, there were an estimated 1,370 water-supply wells in 

the Raton Basin in Colorado, and about 90 percent of these 

water-supply wells were less than 450 feet deep. The depths to 

the tops of the production (perforated) interval of 90 percent of 

the coalbed methane wells in the Raton Basin (for which data 

were available) are greater than about 675 feet. In most of the 

Raton Basin in Colorado and on the basis of estimated thickness of the vertical separation, the potential for interference of 

coalbed-methane wells with nearby water-supply wells likely 

is limited. In most areas, the production intervals of coalbedmethane wells and nearby water-supply wells are separated by 

hundreds to a few thousand feet of rock. Locally, the estimated 

vertical separation between production intervals of coalbedmethane and water-supply wells is less than 100 feet. It is 

assumed that in those areas, production by coalbed-methane 

wells has a greater potential for interfering with nearby watersupply wells. However, more detailed geologic and hydrologic 

information is needed to quantify the potential effects of coalbed-methane production on water levels and the availability 

and sustainability of ground-water resources.

References Cited

Abbott, P.O., Geldon, A.L., Cain, Doug, Hall, A.P., and 

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