UTAH THRUSTS GETTING DEEP LOOKS

G. Alan Petzet
Exploration Editor

Summit County, Utah, will always be remembered as the site of the Pineview field discovery well, which opened production in the U.S. portion of the Rocky Mountain Overthrust Belt in late 1974.

Now, 15 years later, Exxon Co. U.S.A. is conducting deep exploration of complex geology in and near Pineview field in Summit County.

Exxon and Equity Oil Co., Salt Lake City, plan to spud late this month or early in July at 2-7 Bingham, a proposed 12,500 ft geological wildcat on the Pinecliff prospect in Pineview field.

Primary objective near that depth is oil in Jurassic Nugget sandstone and Twin Creek limestone, which produce in Pineview field at 9,000-10,000 ft.

Previous deep drilling at Pineview includes the discovery well, 1 Newton Sheep Co., about 2 miles west of Exxon-Equity's new stake. It bottomed at 14,500 ft.

One other deep test has been drilled through the thrust sheet in Pineview field, but the two zones sought in the new well were not present below the fault at that location.

Exxon is also working in Lodgepole field. It drilled 1 -C UPRC in late 1989 to about 19,500 ft in search of subthrust Cretaceous Bear River. It plugged the well early in 1990 and may have found something promising.

In March 1990, Exxon reentered 2-C UPRC, a depleted Twin Creek oil producing well in Lodgepole field just north of the 19,500 footer. Objective at the reentry is also Bear River at about 17,050 ft.

Bear River at 1,860-2,226 ft pumped 10 b/d of oil and 16 b/d of water in 1988 to open Thomas Canyon field in Uinta County, Wyo. Discovery well was Seale Oilfield Consultants 1-35 Uteland-Federal, near the Utah-Wyoming state line northwest of Evanston, Wyo.

Exxon has not released details of another wildcat, 3 UPRC, drilled in late 1988 less than 1 mile northeast of Elkhorn Ridge field. The well was drilled to about 11,000 ft as a Nugget test.

INGREDIENTS FOR SUCCESS

Exploration along the belt is light these days because not many operators can afford deep drilling in an era of the quick, low risk return.

However, the region has all of the ingredients for one of the largest oil producing provinces in the U.S., P.D. Maher of Energetics Inc., Englewood, Colo., wrote on these pages (OGJ, June 14, 1976, p. 96).

Early drilling established that parts of the belt are rich in source rocks.

"The Cretaceous shales, which underlie the Pineview and Ryckman Creek fields, are probably the source of oil which is being found in the Nugget and Twin Greek formations," Maher wrote in an American Association of Petroleum Geologists paper published here.

He said the belt has hundreds of closed structures on the shallow and lower thrust sheets. Reservoir rocks are abundant with sandstones developed in the Frontier, Dakota, Kelvin, Stump, Preuss, Nugget, the Triassic section, and the Weber, as well as carbonates of the Twin Creek and Thaynes formations.

Exxon was rewarded for its persistent pursuit of the belt last year with discovery of Collett Creek field in Lincoln County, Wyo., about 2 1/2 miles northeast of nearest Big Horn gas-condensate production in the company's Road Hollow field.

The discovery, 1 Collett Creek Unit, 35 miles northeast of Evanston, flowed 601 b/d of oil and 2.11 MMcfd of gas from Ordovician Big Horn at 13,774-920 ft.