Commercial exploitation of gas occluded in coal reservoirs has been hampered by appropriate exploration, drilling, completion and production methods. The Deep Coal Seam Project located at the Red Mountain Site, Mesa County, Colorado is a field laboratory experiment directed to develop, improve, evaluate and communicate the technology required to produce gas from a deeply buried coal reservoir.
Regional geologic studies have established the Red Mountain Site as representative of the majority of the coalbed methane resource within the Piceance Basin. The project is focused on the D coal seam, belonging to the Cameo Coal group of the Williams Fork Formation, Upper Cretaceous Mesaverde Group. Thickness of the D coal seam ranges from 16 to 20 feet (5 to 6.5 m) throughout the site with an average drilling depth of 5500 feet (1800 m). This coal seam is medium-volatile bituminous in rank with an average gas content of 250 scf/ton (8 scc/gm).
The geologic conditions responsible for gas productive coal reservoirs are not fully understood. Data suggests that changes in coal maturation with time and burial depth can create a wide diversity of coal reservoir conditions. Drilling, completion and production methods should be tailored to coal reservoir characteristics, and accurate prediction of coal reservoir conditions need to precede coalbed methane exploitation.
The amount of gas accumulated in a coal seam will be a function of gas generation during the maturation process. Recovery of the gas will be a function of water saturation, cleat permeability, gas desorption characteristics, reservoir pressure, and diffusion rates.