2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 6
Presentation Time: 2:45 PM


AVIS, Loren E., Department of Natural Resources, Colorado Oil and Gas Conservation Commission, 1120 Lincoln, Suite 801, Denver, CO 80203 and MILNE, James J., Walsh Environmental, 4888 Pearl E. Circle, Suite 108, Boulder, CO 80301, loren.avis@state.co.us

Coalbed methane (CBM) development in the Colorado portion of the Raton Basin began in 1993 and continues today. CBM development involves the removal of water from coal seams, which allows methane gas to desorb and to be produced. There are concerns that the dewatering may impact groundwater quality and quantity in shallower horizons and may increase surface gas seepage. In response to these concerns, the Colorado Oil and Gas Conservation Commission (COGCC) completed an environmental baseline study in 2003 to document existing conditions, provide a basis for addressing future complaints about impacts from CBM activities, and monitor areas of concern within the Basin. The study included a methane seep reconnaissance survey, water well and gas well sample analyses, and GIS mapping.

A total of 67 methane seeps were identified, and methane was detected in 114 of the 246 water well samples. Potential shallow sources for methane, such as coal mine shafts, vents, and coreholes were mapped with respect to the methane occurrences. Shallow and deep gas samples were collected from different geologic formations and characterized by isotopic and compositional analyses. Water well and produced water sample results were chemically compared and mapped. Horizontal and vertical separations between water wells and gas wells were also mapped.

The results of this investigation provide interested parties with a valuable initial data set that will allow for focused investigations as needed. Because of the large size of the Raton Basin and complexity of the stratigraphy of the coals in the area, any scientific evaluation of potential impacts from CBM requires not only a large spatially distributed sample set, but an analysis of changes over time.