The central Hanna basin offers multiple hydrocarbon targets in the Mesaverde Group (Campanian Stage), Lewis, Medicine Bow, and Ferris formations (Upper Campanian, Maestrichtian, and Danian Stages). Reservoirs within these formations are found in siltstone, sandstone, coal, and lignitic facies. Permeability is associated with intergranular porosity, microporosity in clays, cleating in coal and lignite, and fracture fields which may be independent of stratigraphic boundaries.
The quality of reservoirs, as determined by logs, is similar to known gas and condensate producing areas of the Red Desert, Washakie, and Wind River basins, in Mesaverde, Lewis, and Medicine Bow (Lance) formations.
Mature oil source is indicated in Medicine Bow and Ferris transitional marine and lacustrine facies (Lance and Fort Union time equivalents). Oil source and sandstone depositional style may be similar to oil productive Fort Union strata in the Wind River and southern Powder River basins.
Source rock studies and time vs. temperature relationships of the Upper Cretaceous lithologic package suggest an area of over 250 mi2 (650 km2) prospective for “tight sands” gas in Mesaverde and Lewis formations to 15,000 ft (4,570 m) and deeper. Lithologic studies of clay and matrix chemistry suggest that specific drilling and treatment fluids are necessary to minimize damage and achieve commercial recovery of gas and condensate.
Recent drilling and modern logging in the Seminoe Unit, T24N, R83-84W, have revealed anomalous gas saturation in Lewis and Mesaverde reservoirs. Numerous reservoirs containing hydrocarbons in the Upper Cretaceous section remain to be evaluated, and the volume of hydrocarbons to be recovered provides reason to proceed.