Abstract: Exploration and Development of Almond Tight Gas Sands Along the Wamsutter/Creston Arch, Wasahakie-Red Desert Basins, Southwest Wyoming

Fred J. Barrett

Along the Wamsutter-Creston arch separating the Washakie-Red Desert basins of southwest Wyoming, the Almond and Ericson Formations of the Upper Cretaceous Mesaverde Group are characterized by a retrogradational sequence of "tight," overpressured, gas bearing, non-marine to marine siliciclastic sandstones. In this study, detailed mapping of Almond-Ericson parasequences was integrated with a detailed core (over 4500^prime from 37 wells), log, and cuttings analysis. A digital core rock and cuttings classification was used to recognize reservoir versus non-reservoir rock types, and different size reservoirs in different depositional environments. Mesoporosity (quartz overgrowth lined) and microporosity (clay-filled) distribution corresponded to vertical and lateral variations in sandstone texture and composition. Porosity and permeability are thus controlled by definitive rock types in the Almond-Ericson sequence. Log measured density porosities are similar to core measured in situ porosities, whereas neutron porosities need a shale correction. The Waxman Smits method for water saturation is preferred, whereas the Archie method calculates wet.

Non-reservoir Almond-Ericson rocks contain less than 8% porosity, less than .005 millidarcies permeability, and greater than 50% irreducible water saturation. Permeability, flow capacity, and hydrocarbon pore volume can thus be calculated for a completion decision analysis based on a consistent water saturation and rock type cutoff. Core, log and production data indicate commercial, areally extensive sands as well as compartmentalized porosity zones in the upper intervals of the Almond Formation. Productive zones in the lower Almond-Ericson sequence tend to be limited in areal extent.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994