COMMERCIAL WILDCAT PLANNED IN SWEDEN'S SILJAN CRATER

A Swedish company, believing the 1 Gravberg in the Siljan crater located an oil reservoir in granitic rock, plans to drill a commercial deep test. Dala Djupgas Produktions AB, Vallingby, Sweden, plans to drill 1 Stenberg in the crater north-northeast of 1 Gravberg, which went to total depth of 22,211 ft. The second well is to start Mar. 15, 1991, and cost 120 million kroner ($21.4 million), compared with 235 million kroner ($41.9 million) for the first well. The 1 Gravberg has three sidetrack

Jan. 14, 1991

4 min read

A Swedish company, believing the 1 Gravberg in the Siljan crater located an oil reservoir in granitic rock, plans to drill a commercial deep test.

Dala Djupgas Produktions AB, Vallingby, Sweden, plans to drill 1 Stenberg in the crater north-northeast of 1 Gravberg, which went to total depth of 22,211 ft.

The second well is to start Mar. 15, 1991, and cost 120 million kroner ($21.4 million), compared with 235 million kroner ($41.9 million) for the first well. The 1 Gravberg has three sidetrack holes.

The same heavy rig, purchased in Oklahoma in 1986 and used to drill 1 Gravberg, will be used to drill the second well, said Tord Lindbo, DDP general manager.

Southern International Inc., Oklahoma City, will provide the drilling crew and supervisory services for the new well.

"We plan to reach our target between 5 km and 6 km, but the cost calculated assumes 7 km," Lindbo said. "The time schedule is 10 months for 7 km with an extra 2 months for unforeseen occurrences plus a 15% contingency."

Funds will be obtained from the capital market by issuing shares in Sweden and other countries, Lindbo said.

Neither the Swedish electric utility Vattenfall, which spearheaded the first scientific deep test, nor Gas Research Institute, Chicago, will contribute to the second well.

The Siljan ring is a crater of granitic rock, overlain by a few meters of soil, thought to have been formed by a large meteorite impact about 360 million years ago.

The impact is postulated to have created fractures at great depth through which gas and oil have been able to migrate, possibly to drillable depths, DDP said.

WHAT WAS FOUND

Extended pump tests in mid-1990 recovered about 85 bbl of an oil sludge from 1 Gravberg.

This result, DDP says, "shows that oil is present in an area and at a depth where no contribution from biological debris can be suspected and where all opinion, based on the conventional theory of oil formation from biological sediments, predicted that neither oil nor gas would be found."

DDP points to recovery of crude oil and odor, color, high nickel concentration, bacteria, ignitability, and salt water.

"During the autumn (1990) three laboratories have accomplished the analysis of the 15 cu m of oil" pumped from 1 Gravberg, a DDP press release said.

"The high concentration of nickel and vanadium provide the strongest evidence that crude oil was being pumped up during the long testing period."

An analysis showed correlations of the oils at depth with oil from surface seeps in the crater, Lindbo said.

"Tests carried out on the surface indicate that a large formation constitutes a reservoir at a depth of 6 km in the center of the Siljan ring," it continued.

ANOTHER VIEW

Robert A. Hefner III, an independent Oklahoma City oilman serving as a consultant to the Swedish drilling projects, said that in addition to the oil the well yielded about 12 tons of "magnetic slime" that contained a distinct bacteriological smell.

"This substance is 'oil wet' and presumed to be complex molecules as they will not dissolve in ordinary solvents, Recent studies indicate that it, too, is principally submicroscopic magnetite presumed to be produced by anaerobic bacteria within the formation," Hefner said.

"Dr. Joseph Suflita, professor of microbiology at the University of Oklahoma, has cultured bacteria at 65 C. from the first sample of this material, and these tests continue."

Hefner is encouraged because gas was encountered throughout drilling, and volumes increased with depth; porous zones were encountered and not tested due to mechanical problems; and the "black paste" that was recovered from about 19,500 ft.

"These significantly interesting facts suggest not only the presence of hydrocarbons but the presence of our biosphere to depths below 20,000 ft with all of the significance this portends," Hefner said.

The 1 Gravberg was drilled in part to test the deep gas theory of the Russian scientist Mendeleev as expanded by Prof. Thomas Gold of Ithaca, N.Y.

The theory holds that methane from great depths ascends towards the earth's surface, carrying with it heavier petroleum molecules that settle out in reservoirs at shallower levels.