Abstract: Coalbed Methane Resource Potential of the Piceance Basin, Northwestern Colorado

Roger Tyler, Andrew R. Scott, W. R. Kaiser

As predicted, from an evolving coalbed methane producibility model, prolific coalbed methane production is precluded in the Piceance Basin by the absence of coal bed reservoir continuity and dynamic ground-water flow. The best potential for production may lie at the transition zone from hydropressure to hydrocarbon overpressure and/or in conventional traps basinward of where outcrop and subsurface coals are in good reservoir and hydraulic communication. Geologic and hydrologic synergy among tectonic and structural setting, depositional systems and coal distribution, coal rank, gas content, permeability and hydrodynamics are the controls that determine the coalbed methane resource potential of the Piceance Basin.

Within the coal-bearing Upper Cretaceous Williams Fork Formation, the prime coalbed methane target, reservoir heterogeneity and thrust faults cause coal beds along the Grand Hog back and in the subsurface to be in modest to poor reservoir and hydraulic communication, restricting meteoric ground water recharge and basinward flow. Total subsurface coalbed methane resources are still estimated to be approximately 99 Tcf (3.09 Tm³), although coalbed methane resource estimates range between 80 (2.49 Tm³) and 136 Tcf (4.24 Tm³), depending on the calculation method used. To explore for high gas contents or fully gas-saturated coals and consequent high productivity in the Piceance Basin, improved geologic and completion technologies including exploration and d velopment for migrated conventionally and hydrodynamically trapped gases, in-situ generated secondary biogenic gases, and solution gases will be required.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana