SOVIET EXPLORATION SUCCESS SPREADS FROM BARENTS INTO KARA SEA

Soviet offshore arctic exploration success has fanned out east of the Barents Sea into the even harsher environment of the neighboring Kara Sea.

Discoveries and geophysical data recently disclosed by Moscow authorities and unofficially by Soviet petroleum industry personnel indicate that shallow waters of the Yamal Peninsula's Kara Sea shelf may hold one of the world's biggest concentrations of giant and supergiant offshore gas fields.

There is little doubt that gas reserves found in the first Kara Sea field exceed the total for all developed Soviet offshore areas combined, including the Caspian and Black seas and the Sea of Okhotsk in the Far East.

That first Kara Sea field, Rusanovskoye, was discovered last year less than 70 miles from the Yamal Peninsula's northwest tip. It could hold gas reserves of as much as 8 trillion cu m (282.4 tcf). If so, it rivals western Siberia's onshore Urengoi field, which has been tagged as the world's largest. It was found astride the Arctic Circle in 1966.

Until Rusanovskoye appeared on the scene, Qatar's North field in the Persian Gulf was generally regarded as the world's largest gas reservoir lying entirely offshore. Its reserves are estimated at 150 tcf.

MORE BIG FIELDS

Soviet maps and sketchy data reaching the West provide evidence that besides Rusanovskoye the southwest arm of the Kara Sea may hold a second supergiant gas field on the Leningradskaya structure about 30 miles south of Rusanovskoye.

Drilling has started or will begin soon on a third large, promising structure, Zapadno-Sharapovskaya, about 80 miles south of Leningradskaya.

Besides those prime targets, the U.S.S.R. has found and will test at least nine other structures in the Kara Sea's southwest arm. Moreover, two giant-possibly supergiant-Yamal Peninsula fields have major extensions offshore under the Kara Sea.

At least one structure on Yamal Peninsula and another on Belyi Island just north of the peninsula, which have not yet been designated as commercial fields, extend into the Kara Sea.

While the Soviets have revealed sparse reserve data on their offshore arctic fields, some western observers believe the Kara Sea's Rusanovskoye field may be twice as large as the more widely publicized Shtokmanovskoye field discovered in the Barents Sea in 1988.

Last April, Moscow newspaper reports estimated Shtokmanovskoye's gas reserves at 4 trillion cu m (141.2 tcf). They said Shtokmanovskoye holds "at least four times as much fuel" as had been attributed to Norway's Troll field in the North Sea.

Shtokmanovskoye was found in a generally ice free area of the Barents Sea in water 200-300 m (656-984 ft) deep. It is believed that Rusanovskoye lies in water no more than 50 m (164 ft) deep but in a Kara Sea area that is navigable only 2-3 months/year without the aid of icebreakers.

Whereas Rusanovskoye is less than 70 miles from the Yamal Peninsula, Shtokmanovskoye is about 200 miles west of huge Novaya Zemlya Island, which separates the Barents and Kara seas, and almost 300 miles north of the nearest point on the European Russian mainland. The field is about 350 miles northeast of the Soviet port of Murmansk.

Studies are under way to determine when development of Shtokmanovskoye can begin under a proposed joint venture agreement between the U.S.S.R.'s Ministry of the Oil and Gas Industry and a group that includes Norway's Norsk Hydro AS along with American and Finnish interests.

It is believed Shtokmanovskoye won't be on production before 2000.

Odds are that the Soviet Union will continue to find more oil and gas fields in the Barents Sea than in the Kara Sea.

Area of the Barents is about 542,000 sq mi with average water depth of 750 ft, while the Kara Sea covers 341,000 sq mi with average water depth of 387 ft.

FIELDS, STRUCTURES MAPPED

A map prepared by the U.S.S.R.'s PA Arktikmorneftegazrazvedka (Arctic Offshore Oil and Gas Exploration Association) shows a scattering of oil and gas fields entirely offshore in the Barents Sea and its southwest extension, the Pechora Sea. This does not include an oil field on the Pechora Sea's Kolguyev Island, where an oil and gas field extends offshore.

The number of structures drilled or which are still undrilled in the Barents Sea far outstrips those shown in the Kara Sea.

But the area of the Barents and Pechora seas in which fields and structures are shown on the new Soviet map is many times larger than the prospective area of the Kara Sea's southwest arm, where the designated Kara fields and structures are concentrated. No fields or structures are shown in the much larger area of the Kara Sea north of Belyi Island off the Yamal Peninsula's northern tip.

James W. Clarke of the U.S. Geological Survey's World Energy Resources Program believes there are good prospects for finding oil along the southern flank of the Kara Sea's submerged North Siberian ridge. The ridge apparently extends east from a point near the northern end of Novaya Zemlya Island to the big Taimyr Peninsula on the central Siberian mainland, which separates the Kara and Laptev seas.

Significantly, oil shows have been found on the most northerly Kara Sea structure designated on the new Soviet arctic exploration map. It is the Byeloostrovskaya structure on Belyi Island's northwest coast and extending off shore.

Most discoveries in the Kara Sea's southwest arm are expected to be gas or gas/condensate fields with mainly Cretaceous pay. Their geological profiles are likely to be similar to those found in Yamal Peninsula fields along the Nurminsky megaarch.

But deeper Kara Sea drilling may tap some Jurassic oil as in Murminsky megaarch fields.

No commercial hydrocarbons are likely to be found on the west side of the Kara Sea's southwest arm and probably not even in the middle sector beyond the Yamal shelf.

The huge Novaya Zemlya trough with water more than 500 m (1,640 ft) deep in some places is on the west side of the Kara Sea's southwest arm. This trough extends virtually the entire length of 500 mile long Novaya Zemlya Island, part of the boundary between the Barents Sea and Kara Sea basins.

Novaya Zemlya, where the U.S.S.R. has been conducting nuclear tests, has no hydrocarbon potential, Soviet authorities say.

The Yamal Peninsula's western shelf is only 250 miles long and 100 miles wide at best. It is in this comparatively small area of 25,000 sq mi or less-only about 7% of the Kara Sea's total expanse-that all of the sea's designated fields and structures are shown on the Soviet offshore arctic exploration map.

NURMINSKY MEGAARCH

The onshore sector of the Yamal Peninsula's Nurminsky megaarch, which trends southeast to northwest, is about 130 miles long. It attains maximum width where it dips beneath the Kara Sea in the area of Kharasavei and Kruzenshtern fields and extends underwater in the direction of the big Leningradskaya structure and supergiant Rusanovskoye gas field.

Besides giant-possibly supergiant-Kharasavei and Kruzenshtern gas/condensate fields with their offshore Kara Sea sectors, the Nurminsky megaarch includes huge Bovanenkovskoye gas/condensate field.

Lying about 30 miles from the Yamal Peninsula's Kara Sea coast, Bovanenkovskoye has been credited with as much as 4 trillion cu m (141.2 tcf) of reserves, easily making it a supergiant by Soviet standards (at least 35.3 tcf).

Giant Neitinskoye and Arkticheskoye fields together with more recently discovered Severo-Bovanenkovskoye gas fields are also on the Nurminsky megaarch.

Both Bovanenkovskoye and Kharasavei have at least 16 pay zones from Jurassic to Upper Cretaceous (Cenomanian), Neitinskoye at least 11, Kurzenshtern at least nine, and Arkticheskoye at least eight.

The prolific Cenomanian gas zones in all Murminsky megaarch fields are quite shallow and are generally topped between 1,700 and 2,650 ft. Small amounts of oil have been found in Kharasavei, Bovanenkovskoye, Arkticheskoye, and Neitinskoye fields.

Despite Rusanovskoye field's location in the Kara Sea's harsh environment, its location is favorable to feed gas into proposed Yamal Peninsula pipelines that likely will run south from Nurminsky megaarch fields to join with the enormous transmission system connecting Urengoi field with European Russia.

Construction of a railway from a point near the base of the Yamal Peninsula to Bovanenkovskoye field began several years ago. But work was suspended or drastically slowed following protests from environmentalists and the small local population of reindeer herdsmen and fishermen.

In fact, the main reason for delaying the railroad's construction may have been the extremely high cost of building an embankment for the tracks across Yamal's swampy-sometimes submerged-terrain.