CBM Water Depletion
Water production from coalbed methane (CBM) wells has the potential to affect groundwater movement to streams and springs where the CBM producing formations outcrop and are near the land surface. CGS has participated in studies of the San Juan, Raton, Piceance, and Sand Wash basins that assess the significance, if any, of these potential impacts. The studies are a joint effort by the Colorado Division of Water Resources, the Colorado Oil and Gas Conservation Commission, and CGS. All these agencies were part of the Colorado Department of Natural Resources at the time of these studies.
CGS defined the geological framework of each basin and CBM producing intervals to identify the primary pathways of groundwater movement. A consultant, S.S. Papadopulos & Associates, used this information in their hydrogeological models to ascertain any current and future impacts to streams. Note for the Sand Wash Basin depletion modelling was not performed because findings indicated that CBM and water production had been very limited so far and that the potential for future development was limited under current economic and technological conditions. Furthermore, geologic complexity of the basin indicated that regional quantitative assessments as originally proposed would not be suitable in this basin. Finally, the DWR oil and gas, produced-water rulemaking process in early 2010 reduced the need for delineating basinwide nontributary areas.
The concern has been raised that the removal of significant volumes of water from aquifers that may be tributary to the surface stream system could be resulting in stream depletions or a reduction in spring flows and/or formation outflows (accretions) that are of a magnitude sufficient to cause injury to senior water rights holders on over-appropriated stream systems throughout Colorado. This water historically has been disposed by one or more methods, including re-injection into deep formations, discharge to the surface stream system, and ponding/evaporation. These studies seek to develop a reliable assessment as to the levels of depletion, definition of the areas where CBM water production is ongoing that might be classified as nontributary, definition of any potential correlations of water quality, geology, aquifer geometry, or formation/well depth that could lead to general guidelines about the potential for stream depletion that would be useful in either prompting or avoiding more detailed studies, and development of recommendations for further data collection or investigations.