Utah’s 30-year prospect

Oct. 2, 2006
After Covenant field in Sevier County, Utah, which opened oil production on the Central Utah thrust belt, where will explorers discover the next potentially giant oil or gas field in the US Lower 48?

After Covenant field in Sevier County, Utah, which opened oil production on the Central Utah thrust belt, where will explorers discover the next potentially giant oil or gas field in the US Lower 48?

Perhaps it will be up the road in Summit County, Utah.

A group led by Double Eagle Petroleum Co., Casper, Wyo., spudded a wildcat at Christmas Meadows, Utah, in late September.

The well is expected to cost $10 million and take 100 days to drill to TD 15,730 ft. Double Eagle cemented 34-in. conductor pipe at 235 ft and 20-in. conductor at almost 1,000 ft before Unit Drilling Co. moved in Rig No. 233 to drill the vertical Table Top Unit No. 1. The drillsite’s surface elevation is 9,573 ft.

Outlays prior to spud totaled $2.5 million for environmental permitting and building the road and location.

The large subsurface feature, a structural dome, appears on numerous 2D seismic lines, but no 3D data have gone into the drilling of this prospect. Overlying the dome, in the southwest corner of the Green River basin, is the Rocky Mountain Overthrust Belt.

Various operators have been attempting to drill this well since the 1970s.

Progressive suitors

The former Gulf Oil Corp. noted the Christmas Meadows prospect on a regional seismic grid in the 1970s.

Later 2D seismic surveys by Gulf, American Quasar Petroleum Co., Amoco Production Co., Chevron Corp., Sohio Petroleum Co., and others supported the dome’s existence.

Amoco staked a location in 1982 to drill a wildcat to 19,000 ft on the structure but had still not been issued a permit in 1986, when it dropped its plans.

Double Eagle first acquired leases on the prospect in 1984. Then Chevron formed a federal unit in 1989 and staked a well but withdrew in 1994, having been unable to get a drilling permit or buy offset acreage offered for sale.

Chevron turned the project over to Amerac Energy Corp., which designated Double Eagle as its agent. Double Eagle acquired the last acreage critical to the prospect at a US Bureau of Land Management auction in November 2003.

Double Eagle holds interests in 42,095 gross acres, of which 22,875 gross acres are included in the Table Top Federal Exploratory Unit.

Seismic search

Double Eagle and partners have acquired licenses to six 2D seismic lines that span 60 miles.

The various exploration organizations reprocessed five lines covering 53 miles with the state-of-the-art prestack depth migration (PSDM) technique.

Imaging and understanding of the structure improved as a result, although the structure map appears similar on all four of the PSDM maps generated, said Stephen H. Hollis, Double Eagle president and chief executive officer.

Hollis said, “It’s a tough seismic area with lots of velocity problems to deal with. The geophysicists would prefer to have 3D seismic, but shooting 3D in a national forest in rough terrain was just prohibitive.”

Not until it reaches 11,000 ft is the well expected to drill out of the last thrust sheet and into the underlying Green River basin, Hollis said.

The Christmas Meadows structure’s position underneath the thrust is similar to that of Utah’s Bridger Lake oil and gas field, which doesn’t produce from beneath the thrust, and the size of the seismic feature is similar to Wyoming’s Anschutz Ranch East gas-condensate field, he noted.

The prospect

The Christmas Meadows structure appears to have prospective formations that range in depth from 4,000 ft to 23,000 ft and in age from Mississippian to Cretaceous.

Obviously a 15,730-ft well will not see the three deepest formations: Jurassic Nugget estimated to be at 17,100 ft, Pennsylvanian Weber at 20,930 ft, and Mississippian Madison at 22,500 ft.

This makes the present wellbore mainly a test of the Cretaceous Dakota and Frontier, Double Eagle said.

The well has about a dozen working interest owners. Double Eagle and one other entity hold 25% each, Unit Corp. has 5%, and Basic Earth Science Systems Inc., Denver, has 2%.