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ARCO, Humble Oil discover the Prudhoe Bay oilfield in 1968 In the second part of a two-part series, Gil Mull describes how the exploration wells struck a massive oil find at Prudhoe Bay Alan Bailey PNA Contributing Writer
In the previous article of this series Gil Mull, a geologist who participated in the discovery of the Prudhoe Bay oil field, told PNA how Harry Jamison of Richfield Oil Corp. drove the exploration of the North Slope between 1963 and 1965. Jamison’s geological and seismic field teams uncovered some possible oil bearing geological structures.
While the exploration was in progress, a flurry of leasing activity had divvied the North Slope acreage between a number of companies. Richfield and Humble Oil had together purchased leases over the crest of a promising looking structure at Prudhoe Bay, while BP, Atlantic Refining, and other companies had separately purchased leases down the flanks of the structure.
Within a couple of years Richfield and Atlantic Refining would combine as Atlantic Richfield (ARCO), while Humble would later become part of Exxon. Drilling at Susie While the lease sales were taking place, Richfield was mobilizing to drill at Susie, a surface geological structure north of Sagwon on the Sagavanirktok River. Equipping the remote drill site at Susie required some innovative thinking.
“They got approval from the Defense Department to lease a Lockheed C-130 Hercules, which up to that time was strictly a military plane,” Mull said. “Nobody had ever done anything like this. They flew the entire drill rig … all the camp, all the casing, everything to the North Slope from Fairbanks.”
The entire operation to move the rig involved more than 80 flights over a period of about three weeks using the C-130 and another cargo plane. The first construction equipment was landed on a gravel airstrip on a river bar at Sagwon and from there was moved overland to the Susie location, where a winter snow and ice strip was built for the subsequent rig move by the C 130 cargo plane.
In 1966 Richfield drilled down through the crest of the surface anticline at Susie.
“That well went down to 13,500 feet and had some oil shows in the … upper part of the hole,” Mull said. Unfortunately, the shows did not prove economic and Richfield abandoned the well in December 1966. Prudhoe Bay With a dry hole at Susie, Richfield decided to drill the major structure that the seismic crew had found at Prudhoe Bay.
“The drilling rig was hauled 60 miles north by cat train to Prudhoe Bay in the late winter of ‘67,” Mull said. The well at Prudhoe Bay was spudded in the late spring and then shut down for the summer, he said.
The drill team returned to Prudhoe Bay in the fall of 1967, after the freeze up. The drilling camp and its attendant ice airstrip looked a forlorn sight in the middle of the vast, snow-covered coastal plain. But Prudhoe Bay State No. 1 well would soon catapult into the forefront of oil exploration history.
In fact, the well looked promising right from the start of drilling. Mull, by then working for Humble, was one of the group of well site geologists for both ARCO and Humble who analyzed the rock samples from the well.
“Early on in drilling that hole we started to get some really good oil shows … and some gas shows,” Mull said. Discovery Then, in December 1967, at 8,200 feet, the well entered the sandstones and conglomerates of the Ivishak formation, which is what is now the main Prudhoe Bay reservoir formation.
“The mud logging readings — the gas readings on the drilling mud and drill cuttings that were coming out of the hole — just went off-scale,” Mull said.
Just after Christmas a well stem test was run, in which the mud pressure in the hole is temporarily relieved to see whether gas or oil would flow into the well bore.
Usually when you run a drill stem test there’s a brief puff of gas and then it dies, Mull said. “This one was not that … there was an immediate huge flow of gas to the surface, which was diverted off into a flow pipe and ignited.
“It was like listening to a jet plane, with the pressure and the roar of this gas flowing.”
The pressure of gas in the pipe was so great that the flare continued burning for 12 to 14 hours after the well was shut well in again, Mull said.
The well drilled on down until it reached an oil column in the base of the Ivishak formation, 400 feet below the top of the gas. Another drill stem test was run in January, after oil was encountered, and this test flowed a mixture of gas and oil.
The first gauged flow of oil on March 12, 1968, was more than 1,100 barrels of oil per day from dolomite in the Lisburne formation, a lower unit that underlies the Ivishak formation, and resulted in an oil flare that looked like a gigantic, horizontal blowtorch. The riches that underlie the coastal plain at Prudhoe Bay had finally appeared.
“So at that time it was clear that the well had both gas and oil in a really good formation, so things got really ramped up then,” Mull said. A second well ARCO and Humble decided to drill a second evaluation well, seven miles southeast from the discovery well and 400 feet down dip to help confirm the size of the field.
For this second well, ARCO hauled in a rig by cat train from the Colville River.
“This was a rig that BP and Sinclair Oil had hauled in by barge from the Mackenzie River in Canada and drilled a (dry) hole on the Colville structure west of Prudhoe Bay,” Mull said.
Alaska Airlines, which had acquired two Hercules C-130 aircraft by this time, started flying in equipment around the clock. Mull recalls trying to sleep in the camp next to the airstrip.
“It was certifiably exciting … there were a hell of a lot of things happening,” he said.
The second well confirmed the discovery. Then, when an independent evaluation by DeGolyer and MacNaughton, an internationally recognized consulting firm, assessed a five to 10 billion barrel find, headlines blazed across newspapers worldwide.
“None of us in our wildest imagination would have dreamed it would be a structure that large and that there would be a 400-foot gas cap on top of a 400-foot oil column in the structure,” Mull said. “As it turned out, the leases that BP had down the flank actually contain about half of the oil.” Did luck play a part? Was the Prudhoe Bay discovery just the result of good luck? Mull doesn’t think so. The skilled team of geologists and geophysicists had delineated prospects in a sedimentary basin with a high potential for oil or gas.
However, there was a bit of luck when the discovery well was positioned at a short distance down from the crest of the Prudhoe Bay structure.
“The reason the well was drilled down dip some … (was) to see more of the stratigraphic section below an angular unconformity,” Mull said. “In fact, if the well had been drilled right on top of the very highest part of the structure, all it would have seen in the Ivishak formation was gas.”
And teamwork provided the key to success on the North Slope: geologists, geophysicists, landmen, construction men, engineers and drillers all played some part in the Prudhoe Bay discovery. Surface geology led to seismic work that led to land acquisition that led to engineering and drilling, Mull said.
But one man, Harry Jamison, really made the whole thing happen, when he initiated the Richfield exploration back in 1963 and when he insisted on the need for a seismic survey on the North Slope.
“There’s not a shred of doubt in my mind that if Harry hadn’t been there, and ran Gar Pessel’s note up to the upper level management to get a seismic crew authorized … Atlantic Richfield and Humble (Exxon) would not have had the position they had on the North Slope,” Mull said. “He was the sort of spark plug to get these things going.
“And nearly 40 years later we continue to see the results of Jamison’s persistence.”
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