Title: The Coalbed Methane Potential in the Upper Cretaceous to Early Tertiary Laramie and Denver Formations, Denver Basin, Colorado
Speaker: Laura L. Wray, Colorado Geological Survey
Date: March 1, 2002
Publication: The Outcrop, March 2002, p. 4-5
Coals in the Late Cretaceous Laramie Formation and early Tertiary Denver Formation hold some intrigue for coalbed methane potential by virtue of their measured heating values, shallow depths, areas of reasonable thickness and continuity, and the documented occurrences of gas accumulations and explosions in coal mines.
Over the past 140 years, more than 300 historic mines were developed in the Denver Basin. The vast majority of them were underground mines in the Laramie Formation coals from which approximately 130 million tons of subbituminous coal was mined. Now that newly developed completion technologies are allowing commercial methane production from shallow, low rank coals, even the Denver Formation lignitic coals, mined in the past in small quantities, may be prospective.
The great diversity in coalbed methane plays proves that there are various reservoir characteristics critical to successful methane production from low rank coals. Preliminary analyses of coal data collected by mining companies, combined with data collected from gas, oil, and water wells drilled in the Denver Basin, strongly suggest that further research and testing is required to demonstrate the economic feasibility of a coalbed methane play in the basin. In order to assess the preliminary potential of these coals, the Colorado Geological Survey has compiled a Geographic Information System (GIS) coalbed methane database that captures the data contained in numerous hardcopy publications released over the past twenty years. The GIS ArcView™ format allows easy manipulation of important data such as isopach and structure maps, log cross sections, desorption and heating value data, locations of historic mines, coal analyses from those mines, and calculated gas content values.
Original gas in place and recoverable reserves for Denver Basin coals were estimated using analogies from the low-rank Fort Union Formation coals that produce methane in the Powder River Basin. The respective values for both formations are 2.4 trillion cubic feet (TCF) and 2.2 TCF which closely approximate the resource estimate of 2.0 TCF made by the Gas Research Institute (now the Gas Technology Institute) several years ago. Two-thirds of this resource exists within the Laramie Formation.
In addition to evaluating the resource potential, careful consideration must be paid to the shallow aquifers that surround and include these coals and into which thousands of water wells have been drilled. Before coalbed methane production becomes a reality, further research is imperative to establish whether the coals and aquifers are hydraulically connected and what statutory authorities must be established to handle the issues of produced water from coal beds. Clearly, regulatory and environmental factors will play vital roles in determining the producing potential for a coalbed methane play in the Denver Basin.