PAIR OF MONTANA TESTS LOOKS AT OVERTHRUST

John McCaslin
Exploration Editor

When drilling weather returns to western Montana, regional exploratory eyes will be on a pair of wildcats to be drilled in the Helena salient of the western Montana Overthrust Belt.

Balcron Oil of Billings announced this winter the locations for a pair of exploratory evaluations of the region. The remote wildcats, only one half mile apart, will be drilled 32 miles southeast of Helena and south of the Elkhorn Mountains on a large structure, according to a report in Montana Oil Journal of Billings.

These interesting sites lie 120 miles west of Lake Basin gas field and 140 miles south-southeast of Blackleaf Canyon, a milestone belt Mississippian gas field which produced in folded and faulted Madison rocks.

BADLY NEED WILDCATS

Although most of the oil and gas production from the Overthrust Belt comes from southwestern Wyoming and northeastern Utah, older discoveries at Two Medicine Creek and Blackleaf Canyon field in western Montana suggest that more hydrocarbons lurk in other spots along this belt of highly complex geology-Balcron's announcement is a welcome report to the industry which seeks an exploratory revival in the U.S. And what better place to begin ... western Montana.

The two staked locations are on private leases in NE SE 2-4n-2w and NW NE 11-4n-2w, eastern Jefferson County, Mont. Montana Oil Journal notes that according to surface mapping in the area, the well will spud in Precambrian Belt rocks about 18 miles west of the leading edge of the Lombard thrust plate, an extension of the Eldorado thrust and Lewis thrust to the northwest.

Objectives for the 13,500 ft Balcron project are potential oil or gas reservoirs in the thrusted Phanerozoic, particularly the Mississippian Madison rocks, in the imbricate stacks below the 4,000 to 7,000 ft of Precambrian Belt, according to the Journal report. The well sites are very near the axis of the huge north-south trending Devil's Fence anticline, a feature that is expressed on the surface for about 20 miles.

IN A WELL-BARREN SECTOR

Oil-well drilling in this part of Montana has been sparse.

Only about six wildcats have ever been put down in Jefferson County, for example. Only one of three went to 1,000 ft. Montana Oil Journal notes that the closest drilling was 7 miles south to 130 ft. Needless to say, the logs from the new Balcron tests will be very interesting.

The overthrust section in the area to be looked at by Balcron is expected to be thinner than the thrust sheet encountered by Union Oil at Canyon Creek Prospect, 55 miles northwest. Montana Oil Journal reported on 11-29-89 that this wildcat drilled under the Eldorado thrust plate. No data were released by Union other than the record total depth at 17,818 ft. Reports from the region suggest that Union may have penetrated more than 10,000 ft of Belt rocks before breaking through the overthrust.

Montana Oil Journal adds that the lands being looked at here are south of the Helena National Forest. Balcron has formed an 80,000 acre federal unit around the locations.