Print this pageModeling Burial and Thermal History of the Mesaverde Group, Piceance Basin, Colorado - Implications for Gas Generation from Coals
COMER, JOHN B., DOROTHY F. PAYNE, and WALID SIBO
Burial and thermal models that are well constrained provide insight into the development of tight gas sandstone reservoirs in the Upper Cretaceous Mesaverde Group (lies and Williams Fork Formation), Piceance Basin, Colorado. As much as 2,000 meters of sediment accumulated in the basin between 77 and 66 Ma. The lies Formation consists of several progradational (regressive) shallow marine and shoreface sandstones (Sego, Corcoran, Cozzette, Rollins) separated by tongues of marine Mancos Shale. The Williams Fork Formation consists of coal-bearing sequences and nonmarine sandstones and shales that represent fluvial-deltaic or wave-dominated clastic shoreline deposits. The Sevier orogeny (160-72 Ma) produced regional east- west compression, and rapid subsidence commenced near the end of this tectonic episode. The Laramide orogeny (72-40 Ma) caused regional uplift and differential basin subsidence, and Mesaverde strata reached maximum burial depths near the end of this tectonic episode. After the Laramide, the Piceance Basin experienced basin and range extension and, in the southern part of the basin, igneous intrusion and volcanism.
Gas in Mesaverde reservoirs originated primarily from Mesaverde coals. Thermal generation began in the deepest and hottest parts of the basin during the Eocene. In many parts of the basin gas generation has slowed or ceased due to post-Laramide uplift and erosion. Gas generation coincided, for the most part, with the development of fractures that constitute the effective reservoir porosity.