Abstract

Notches Dome is located on the northwestern end of the Casper Arch on the asymmetrical, southeast plunging Cottonwood Creek Anticline near the junction of the Owl Creek and Bighorn uplifts in central Wyoming. Notches Dome Field was discovered in 1923 by the Midwest Refining Company. A total of 29 wells have produced a cumulative of 10 million barrels of oil from the Pennsyluanian Tensleep Formation occurring at an average depth of 3,000 feet. In early 1988, the field produced at a combined rate of 360 barrels of oil and 30,000 barrels of water per day from 13 wells. PEOC's drilling program, initiated in August 1988, resulted in 10 additional productive wells increasing production to 2200 barrels of oil and 50,000 barrels of water per day. This project developed 2 million barrels of new oil reserves.

In 1988, PEOC conducted a detailed review of the aging Notches Dome Field and determined that the productive limits had not been defined. Both surface and subsurface mapping, later supplemented by 6 miles of proprietary seismic data, revealed a previously unrecognized nose and new geometric configuration for the dome which is best illustrated as a trap-door type structure. The primary trapping mechanism consists of over 300 feet of four-way structural closure.

PEOC drilled the first productive extension well on the southwest flank of the dome on a nose structurally flat to the lowest producing well in the field. They found most of the new reserves along this flank, as it was unaffected by water migration. A northeasterly hydrodynamic flow trapped the oil along this flank and is demonstrated by a temperature gradient map having an unusually high temperature anomaly at the northeast edge of the field. The new geometric configuration and temperature anomaly indicates water flow from the northeast through faults and fractures from deeper horizons.