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
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The citation for this report, in USGS format, is as follows:
Watts, K.R., 2006, 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:
U.S.
Geological Survey Scientific Investigations Report 2006-5109, 9 p.
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 coalbed-
methane 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 water-supply 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.
Table of Contents
Abstract
Introduction
Purpose and Scope
Hydrogeologic Setting
Depths of Water-Supply Wells and Production Intervals of
Coalbed-Methane Wells
Ground-Water Pumping
Vertical Separation between Production Intervals of Coalbed-Methane
Wells and
Water-Supply Wells
Potential Changes in Water Levels Resulting from Coalbed-Methane
Production
Hypothetical Effects of Coalbed-Methane Production
on Nearby Water-Supply Wells
Estimated Vertical Separation between Production Intervals
of Coalbed-Methane and Water-Supply Wells
Summary
References Cited
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