Coalbed Methane

Intro

Coalbed methane (CBM) is natural gas produced from subsurface coal deposits. Much of the technology uses standard well-drilling and production techniques. The primary difference is the total usage of water in the process. In most cases, water must be pumped out of the formation in order to allow the methane that is adsorbed onto the coal particles to escape and travel to the surface via extraction wells.

Typical natural gas wells reach a peak and then begin a volumetric decline in production relatively rapidly. Coalbed methane wells behave differently. They increase in production for a long time as more and more water is removed from the strata. Decline in production does not usually begin until late in the life of the well.

CBM production in Colorado reached its highest levels, 59%, of total natural gas production during 1998 and has continuously declined to ~11% of the total natural gas production in 2020. This decline is largely due to the increase of natural gas production of unconventional reservoirs by the utilization of horizontal drilling and hydraulic fracturing techniques. As of 2017, Colorado contained about 27% of U.S. CBM reserves.

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. The CGS participated in studies of the San Juan, Raton, Piceance, and Sand Wash basins that assessed the significance, if any, of these potential impacts. The studies were a joint effort by the Colorado Division of Water Resources (DWR), the Colorado Oil and Gas Conservation Commission, and the CGS. All these agencies were part of the Colorado Department of Natural Resources at the time of these studies.

The 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 modeling 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 rule making process in early 2010 reduced the need for delineating basin-wide non-tributary 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 non-tributary, 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.

Resources

Energy and Carbon Management Commission (ECMC) – Colorado Oil and Gas Information System (COGIS) — The ECMC regulates non-renewable energy production in Colorado including coalbed methane and issues reports on both production and stream depletion.

Global Methane Initiative (GMI) — An international public-private partnership focused on reducing barriers to the recovery and use of methane as a clean energy source.

United Nations Economic Commission for Europe – Group of Experts on Coal Mine Methane — The principal activity of the Group of Experts on CMM is development and dissemination of the Best Practice Guidance for Effective Methane Drainage and Recovery in Coal Mines.

U.S. Department of Energy – Energy Information Administration – Colorado coalbed methane production — A variety of statistics on production with links to other resources.

U.S. EPA – Coal Mine Methane Project Resources — Resources and tool to maximize profitable methane reductions.

U.S. EPA – Coalbed Methane Outreach Program (CMOP) — CMOP works cooperatively with the coal mining industry in the US to reduce coal mine methane emissions.

U.S. Geological Survey – The Energy Resources Program — Research advancing the understanding of US energy resources including coalbed methane.