ABSTRACT: Shallow Gas Production from Sandstone Reservoirs in the Fort Union Formation, Powder River Basin, Wyoming

OLDHAM, DAVID W., West Virginia University, Morgantown, WV

The occurrence of natural gas in sandstones and coal beds in the Tongue River Member of the Fort Union Formation (Paleocene) in the Powder River basin is known from shallow gas shows and minor production from coal test holes, water wells, and deeper oil and gas tests. Recent exploration and drilling efforts have demonstrated that significant gas production can be established from the shallow sandstone reservoirs.

Production has been established from sandstones that occur below the Anderson, Canyon, Cook, and Wall coal beds. Gas-productive zones range in depth from less than 200 ft to about 600 ft. Reservoir porosity exceeds 35%. Wyatt Petroleum Corporation's Oedekoven 83-1 and 83-2 wells in the Oedekoven field have produced in excess of 300,000 MCFG and 500,000 MCFG, respectively. Subsequently drilled wells in the Chan field, located five miles northeast of Cedekoven field, are expected to yield comparable production figures.

Chemical and isotopic analysis by the U.S. Geological Survey and others of gas produced from the Fort Union Formation suggests a biogenic origin, with the thick, subbituminous-rank coals serving as source rocks. Because biogenic gas is generated early in the coalification process, a search for traps that existed soon after deposition is the basis for the exploration approach. Subsurface mapping of sandstones and coal beds indicates that potentially gas-productive paleostructures are formed as a result of differential compaction.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)