Offshore riches: bubble, bubble, oil and trouble

Sometime about 100 million years ago, the North Atlantic opened up like a big zipper. Nova Scotia, then believed to be part of Europe and North Africa, parted ways with Morocco. Newfoundland cracked off from Spain.

When the two Canadian provinces finally came to rest, mud deposits sealed the rocky underwater vaults off their coasts which today hold some of the world's most promising oil and gas reserves.

But earthshaking political and technical problems need to be solved before energy can be extracted from the undersea tombs.

For now, the pace of exploration off the east coast of Canada is slowing. Jitters over the Trudeau government's national energy plan, plus Newfoundland's continuing squabble with Ottawa over control of the offshore energy, have prompted some companies to scale back plans.

About a dozen rigs were originally slated to drill in waters off the fog-shrouded Newfoundland coast this summer, but only six showed up. By year's end, companies will have spent an estimated $360 million (US $302 million) searching for oil and gas in 1981.

Since 1966 at least 73 holes have been punched in the area. That number is expected to more than double over the next decade. The biggest flurry of activity came after the Hibernia P-15 strike in late 1979. The reservoir in the Grand Banks fishing area 192 miles southeast of here is believed to hold 1.85 billion barrels of oil and 2 trillion cubic feet of gas - the largest North American petroleum find since Alaska's Prudhoe Bay.

Some analysts believe the pattern of discoveries around Hibernia and in the whole Canadian Atlantic region shows a North Sea-sized field. Of the wildcat wells drilled so far, about 1 in 8 has hit crude - a good batting average by world standards. Mobil and its partners have yet to declare Hibernia a viable venture, largely because of the federal-provincial energy fray.

''We can't serve two masters,'' says Susan Sherk, of Mobil Oil Canada Ltd. ''We need to know how a government is thinking five years down the road. We're in a holding pattern.''

One problem oil companies face in drawing up the energy is icebergs. These behemoths have been known to ''scour'' trenches 10 feet or more into the ocean floor. Oil company officials, as a result, would prefer to shuttle the oil in tankers instead of laying a pipeline and are leaning toward using mobile, floating production platforms.

This makes Hibernia a tough technical test for the oil companies - and an expensive one. It's estimated it will cost $5 billion to $8 billion to develop the field, so the petro companies are moving cautiously. ''The government keeps talking about it (Hibernia) being commercial,'' says Mobil's Ms. Sherk. ''It's not commercial. It's not the size, it's the wellhead price that counts.'' And that hangs on government decisions.

In the meantime, Newfoundland insists on some of the benefits from oil company activities. The government projects some 9,300 jobs will be created over the next decade as a result of new offshore exploration activity. That number would rise if Hibernia were developed. But it will take several commercial fields to dent significantly the more than 30,000 jobless rate, particularly in rural areas.

Nor is the province likely to turn into a wealthy Arab state in the near future. At most, provincial revenues from Hibernia are projected to add up to a net additional $4.1 billion in Canadian dollars by 1992. (Gross revenues would be greater, but this net figure subtracts the anticipated decline in federal subsidies as the province becomes wealthier.) Under proposed federal oil revenue-sharing rules, it would be $2.2 billion. Either way, the province would still have a way to go before it could eradicate its debt, pay off its borrowing bills, and reduce taxes.