50 years has passed since Prudhoe discovery

Knowledge, educated guesswork, science, and a willingness to spend money by relatively small companies led to a giant oil find

Compiled by Kay Cashman

Petroleum News

Despite Richfield’s growing enthusiasm for North Slope exploration, limited budgets probably would have quashed the company’s oil hunting efforts in the Arctic were it not for a 50-50 strategic partnership with Humble Oil & Refining Co, a subsidiary of Exxon and eventually folded into Exxon. Humble brought money, technology and field expertise to the exploration team, the deal driven in part by the companies’ desire to bid on leases in the state of Alaska’s first North Slope lease sale in December 1964.

“That partnership has to have been one of the all-time great deals for Humble,” said Gil Mull, a Richfield geologist who went to work for Humble in 1967. “It bought into half of everything Richfield had done to that point (which included surface field mapping, seismic data and federal leases previously acquired) - all for $1.5 million in cash and an obligation to pay for another $3 million worth of seismic data. … After the partnership came on, we ran seismic lines farther up north,” he said, noting there were “two of us from Richfield and two of us from Humble” in the field.

More money flowed into the partnership from Humble as time went on.

In 1966, Richfield merged with Atlantic Refining to eventually become ARCO; it and Humble spent more than $4.5 million on the Susie No. 1 well, just north of the Brooks Range foothills on the Sagavanirktok River. Susie had oil shows but not enough to be deemed commercial and was abandoned in early 1967.

Humble selects discovery well location

Bay State No. 1 with a cat train in February 1967. Bob Jacobs, a pilot for Interior Airways, took the photo.

J.R. Jackson Jr., Humble’s Alaska exploration manager, reviewed structural maps from seismic work. He detected an anticline, or a dome, almost football-shaped, and was convinced that if there were oil and gas it would migrate to the dome and be trapped there.

So Jackson pleaded his case to Humble’s board of directors.

“They weren’t hot on it, but he sold them,” said Crandall Jones, who served as Humble’s Alaska exploration manager following the discovery. “He and the exploration management team convinced them it was worthwhile to have one more try. … That one more try was a discovery well.”

In 1966, North Slope geologist Marvin Mangus became senior field geologist for ARCO.

Mangus also thought the location would be a good place to drill, in part because of the subsurface clay.

“We took it to management, and they said go ahead. We were all in favor of drilling it - Charlie Selman, head of geophysics, Rudy Berlin, Gil Mull, John Sweet and Harry Jamison. … When we put it all together, from geophysics to geology, Prudhoe Bay State No. 1 was our discovery,” he said.

Nominated to spend Christmas at Prudhoe Bay

“Although ARCO was the operator on the well, Exxon’s Humble … wanted to have its own geologist to observe operations and to assist the ARCO geologists with sample examination and evaluation of the stratigraphy encountered in the well. ….

“I was nominated to spend Christmas on the North Slope for the second year in a row.”

The camp consisted of two parallel rows of ATCO trailers strung together end-to-end and roofed over with sheets of plywood. … The drill rig stood about 100 yards away at the east end of the camp.

“Only a short time before my arrival, the well had reached the top of the Sadlerochit formation (also known as the Ivishak formation) at a depth of 8,208 feet, and things were beginning to become interesting. ….”

Although there had been some oil and gas shows higher in the well, “methane gas readings in the drilling mud abruptly went off-scale in the Sadlerochit - which was a really encouraging sign,” Mull said.

“Inasmuch as there was no way of predicting with any level of confidence how thick this interval might be, drilling progressed slowly. ...

“By Christmas day, the well had penetrated over 350 feet of predominantly sandstone and conglomerate, accompanied by continued high gas readings in the drilling mud, and oil shows in some of the lower core samples. This was a phenomenal thickness of potential reservoir beds and the decision was made to run an open-hole drill stem test to determine the flow capability of the lower 180 feet of the Sadlerochit.

“The test tool was opened early in the morning of Dec. 27, 1967, with a result totally unlike anything I had ever previously experienced in a drill stem test. In the tests that I had witnessed … on other wells, all that happened when the tester was opened was a weak puff of air flowing from the drill pipe, which then died to nothing. In this test, there was an immediate roar of high-pressure gas flowing to the surface, which was diverted to a flow pipe and ignited to make a flare that was up to 30 feet long blowing into the teeth of a headwind.

“The gas flow was estimated at 1.25 million cubic feet per day through a 1/8-inch choke at a pressure of over 3,000 psi. This continued all day, with a rumble that shook the rig and resembled the sound of a jet plane overhead. The pressure was so great that after the test tool was closed late in the afternoon, the flare burned most of the night as the high pressure in the drill pipe bled down.”

Looked like gas discovery

The test tool was opened early in the morning of Dec. 27, 1967 on Prudhoe Bay State No. 1 with an immediate roar of high-pressure gas flowing to the surface, which was diverted to a flow pipe and ignited to make a flare that was up to 30 feet long. The pressure was so great that after the test tool was closed late in the afternoon and continued to burn most of the night. Note drifting snow in foreground.

“By the morning of Dec. 28, the gas pressure in the drill pipe was finally exhausted and at last the drill crew was able to begin to come out of the hole with the drill pipe and test tool,” Mull said.

“But by that time, the bottom of the hole had begun to cave, and the 8,500 feet of drill string and DST tool could be moved only a few feet up and down. The tester and lower part of the drill string were stuck in the hole, and a fishing job was begun.”

The well had penetrated a high-pressure gas reservoir that was at least 385 feet thick, with no indication of either a gas-oil or gas-water contact.

“It was beginning to appear that Prudhoe Bay might very well be a significant gas discovery,” Mull said, but oil was the objective.

There would be no need for geologists at the well site for some time, so Mull flew back to Humble’s Los Angeles office.

ARCO and Humble decided to “side-track the lower part of the original hole and drill around the stuck fish.”

“The base of the Sadlerochit sandstone and conglomerate interval was finally reached at 8,670 feet - an interval thickness of over 460 feet with about 300 feet net sandstone and conglomerate as potential reservoir beds. Even more significantly, the lower 40 feet of the sandstone was oil saturated, and no oil/water contact was encountered,” Mull said.

“After wire-line logs were run, a string of casing was set through the Sadlerochit and drilling continued into the underlying Lisburne formation, which was found to consist of hard limestone with interbedded brown, porous, oil saturated dolomite.

“Another open-hole drill stem test in the top of the Lisburne recovered light oil that flowed intermittently with a high volume of gas. This test showed that the Lisburne was also an oil reservoir, but the flow of gas suggested that there was communication with the overlying Sadlerochit formation, which was behind casing.

“During the DST, some of the high-pressure gas from higher in the well was apparently bypassing the cemented casing and into the lower part of the hole, where it flowed with the oil from the Lisburne.

“The level of excitement on the well was increasing. Although the rate of oil flow during the test could not be measured, the discovery of oil in the well was headline news in the Feb. 16 Anchorage Daily Times.

“By the end of the first week of March, we had drilled and cored over a thousand feet of Lisburne that contained a number of thin beds of oil-saturated dolomite. Another drill-stem test was run, to test a 320-foot interval in the lower part of the Lisburne. This test was a spectacular success.

“About 20 minutes after the test tool was opened, the light flow of air from the drill pipe was followed by gas to the surface and then in about two hours oil began flowing to the surface. Oil flowed for 7 hours at a measured rate of 1,152 barrels of oil per day; this test confirmed beyond any question that Prudhoe Bay State No. 1 was a significant oil and gas discovery,” Mull said.

In addition to Lisburne, the Sadlerochit formation was “clearly an even better reservoir unit,” he said.

But the height of the oil column was unknown so ARCO and Humble management decided a second well and more evaluation was needed.

Major deployment got underway

Thus began a massive mobilization of equipment.

In mid-March, while drilling continued at Prudhoe Bay No. 1, an airlift began and two Alaska Airlines C-130

Hercules cargo planes began flying around the clock from Fairbanks. The Prudhoe well site was a beehive of activity as about every two hours, night and day, another Hercules would taxi into the ramp just outside our sleeping trailer and offload another 40 tons of equipment, Mull said.

The second well, Sag River State No. 1, “was to be near the banks of the Sagavanirktok River, seven miles southeast of the Prudhoe Bay drill site.”

“By May … drilling was progressing rapidly. Hank Repp, Dean Morgridge, and I took turns as the Humble well site geologists, working with ARCO geologists Marv Mangus, Bill Pentilla, and Bob Anderson (no relation to R.O. Anderson). ….

“By early June, the top of the Sadlerochit was reached and was being evaluated by almost continuous coring. Most of the Sadlerochit was within the oil column, and some of the sandstones and conglomerates appeared to have even better reservoir quality” than at Prudhoe Bay State No. 1, Mull said.

“Security was very tight, and only the geologists were supposed to see the rocks that were being extracted from the core barrels, but one 20-foot core was particularly memorable.

“Usually, a solid cylinder of rock came out of the core barrel and was laid out in trays to be examined in detail. But in this case, with the core barrel hanging vertically in the derrick, when the core bit was removed from the barrel, out poured a pile of unconsolidated sand, gravel, and oil - which flowed through openings in the derrick floor and into the rig cellar. The porosity and permeability of this interval was fantastic. ….

“The Sag River field confirmation well showed that the Sadlerochit reservoir interval was over 500 feet thick, with at least 300 feet of net reservoir-quality sandstone and conglomerate, and a 400-foot oil column below a gas cap that was also about 400 feet thick,” Mull said.

On July 18, ARCO and Humble released the results of an independent evaluation of the Prudhoe Bay State No. 1 and Sag River State No. 1 wells, saying Prudhoe contained between 5 billion and 10 billion barrels of oil, making it the largest oil field in North America.

Editor’s note: See part 2 in the next issue of Petroleum News about BP’s Prudhoe confirmation well, the results of which came in March 13, 1969, announcements in London and New York.