Mesaverde Tight Gas Sandstone Sourcing from Underlying Mancos-Niobrara Shales
Stephen Cumella and Jay Scheevel
Recent drilling of Mancos-Niobrara shales in the Piceance has identified a significant gas resource in the southern Piceance Basin, where numerous vertical and horizontal wells have encountered thick shale intervals with pervasive gas saturation that are locally highly pressured. Pressure data indicates Mancos-Niobrara pressure gradients near 1 psi/ft in some areas. Geological and geochemical data indicate that the Mancos-Niobrara has been a major source of gas for the overlying Mesaverde tight-gas accumulation. Vertical gas migration from thick, shaly Mancos-Niobrara to the Mesaverde may have occurred primarily along fault and fracture zones. The top of continuous gas saturation rises significantly adjacent to major structural features such as the Rulison nose, the Crystal Creek anticline, and the Gibson Gulch graben. Mesaverde gas production is commonly enhanced in these areas. Very high capillary pressures are required to achieve the low water saturations that have been measured in Mesaverde sandstones that have microdarcy permeability. High capillary pressures could have been provided by vertical migration of highly pressured gas from the Mancos-Niobrara into the Mesaverde. Additionally, the highly pressured gas would have enhanced natural fracturing during migration and filling of the tight sandstone reservoirs, while significantly increasing reservoir permeability.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012