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New drilling-effect study focuses on water quality, quantity
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CopyLAS ANIMAS COUNTY
TRINIDAD - The Colorado Geological Survey is planning a study of die effects of coalbed metiiane drilling on water quantity and quality of the Purga-toire River Basin upstream of Trinidad.
The study, which is to be conducted beginning diis month and stretch through June 2010, will seek to compile current and historic stream flow levels; characterize the quality of ground and surface waters in die river basin; determine die relationship between coalbed methane (CBM) "producing intervals" -- a given time period when a production wellhead is working -- aquifers and surface formations, and create a groundwater-level monitoring system and determine the hydraulic storage capacities of me bedrock (how much water it can hold) and alluvial aquifers (those formed by deposits of things such as sand and silt).
"This is really a follow-up to a stream depletion analysis that was done by multiple state agencies -- the Colorado Oil and Gas Conservation Commission (COGCC), the Division of Water Resources and our own agency," Colorado Geological Survey (CGS) Senior Hydrologist Ralf Topper said. "That was a first look at trying to answer the question, is there an impact from CBM production on water rights? That study indicated tiiat, yes, tiiere was an impact to stream depletion."
According to the U.S. Geological Survey, coal stores six to seven times the amount of gas tiian can be found in the equivalent rock volume of a conventional gas reservoir. In order to harvest the natural gas from die coal, die coal's pressure levels must be reduced, which is accomplished by removing water from the coal bed. The water is often injected back into the ground at a deep level, but can also be dissolved in surface evaporation pits.
Topper said that one of the objectives of the upcoming study is to, "...further characterize the hydrogeology of the aquifers and look at water quality to see if there is an impact from CBM on water resources. We're going to look at both the quality of ground and surface water, specifically in the Purgatoire River Basin."
The governmental study mentioned by Topper was conducted by contractors S.S. Papadopulos and Associates beginning in December 2006 witii findings released in January 2008. That study's primary objectives were given as developing a quantitative assessment of die stream depletion levels mat might be occurring as a result of die removal of water by CBM wells, along witii providing an overview of die state of water in die Colorado portion of die Raton Basin as it relates to CBM production. The basin is approximately 50 miles east-west, and 90 miles north-south, stretching across Huerfano and Las Animas Counties in Colorado, and Colfax County in New Mexico.
The study estimated the depletory effects at 1,150 acre-feet using an analytic model known as the Glover-Balmer Model (GBM). The GBM is an analytical tool devised in 1954 to determine, "...the ratio for stream depletion to total pumpage at any given time for a well pumping from an aquifer fully penetrated by a stream."
However, a second study, jointly commissioned by Pioneer Natural Resources and XTO Energy and released last fall, suggested that the effects of CBM drilling on water levels in the basin were negligible.
A summary of the study's findings released by energy industry consultants Norwest Applied Hydrology used the mathematical model MODFLOW to potential effects of CBM drilling on the basin's water levels. An "industry standard" numeric groundwater flow modeling code also used by the U.S. Geological Survey, MODFLOW found the CBM-related depletions from the Pur-gatoire River to be less than 30 acre-feet.
The upcoming study, however, is not model-based. "We're not trying to simulate groundwater flow, we're really trying to characterize the geologic relationships between the producing intervals, the water-supply aquifers and the formations at the surface," Topper said. "Many of the models treat geology as a layer-cake, with specific layers representing specific geologic layers: coal, sands...in reality, the geologic environment varies dramatically horizontally, spatially, (so) perhaps a specific producing interval is quite different at the surface than at the subsurface."
The results of the study are expected to be released a few months after the June 2010 completion of the study, possibly by the end of that summer, according to Topper. The study was made possible by a $125,000 severance tax grant from the Colorado Water Conservancy Board.
Copyright 2009 The Raton Range, Raton, New Mexico. All Rights Reserved. This content, including derivations, may not be stored or distributed in any manner, disseminated, published, broadcast, rewritten or reproduced without express, written consent from SmallTownPapers, Inc.
© 2009 The Raton Range Raton, New Mexico. All Rights Reserved. This content, including derivations, may not be stored or distributed in any manner, disseminated, published, broadcast, rewritten or reproduced without express, written consent from DAS.
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