Christmas at Prudhoe Bay
Personal reflections from Alaska geologist Gil Mull, who sat on the Prudhoe discovery well for Humble, ExxonMobil predecessor
For Petroleum News
It was totally unexpected; it was mid-December 1967, not long before Christmas, and there I was, suddenly on an airline flight from Los Angeles to Fairbanks, where I transferred to a bush flight heading for the Prudhoe Bay State No. 1 drill site.
Although ARCO was the operator on the well, Exxon’s Humble Oil & Refining was a 50 percent partner in the well and wanted to have its own geologist there to observe operations and to assist the ARCO geologists with sample examination and evaluation of the stratigraphy encountered in the well.
The well was a rank wildcat, located 60 miles from the nearest well or outcrop control, so that prediction of the stratigraphy to be expected in the hole was based on seismic control and projections from what we had seen in our outcrop mapping during our summer field work.
I’m sure management had not originally planned to send me up as the Humble well site geologist, because I was a relatively inexperienced, recently hired junior geologist with less than six months with Humble. But, unexpectedly, my colleague Bill Schetter, who was the Humble well site geologist on the well, announced that he had accepted a college faculty position to teach geology, and suddenly the company needed someone to replace him.
I had had three years of field mapping experience with Richfield Oil (ARCO Alaska/ConocoPhillips predecessor) in the Brooks Range and on the North Slope before I joined Humble and thus was familiar with the North Slope stratigraphy and the Prudhoe prospect. And, I also had well site experience as one of the ARCO well site geologists the previous winter on the Susie Unit No. 1 well - a dry hole in the foothills 60 miles south of Prudhoe Bay.
Thus, although my specialty was outcrop geologic mapping, I was nominated to spend Christmas on the North Slope for the second year in a row, to represent Humble and assist ARCO geologist Marv Mangus and his alternate Bill Pentilla.
Things were becoming interestingAs the bush flight crossed the Brooks Range and out onto the North Slope in the mid-winter darkness, a single light in the distance became visible - the rig lights at the Prudhoe Bay well site - our destination. The airstrip was a snow and ice strip on the tundra, and in the mid-day twilight the plane taxied up to an unloading ramp right outside the camp and the drill rig.
The camp consisted of two parallel rows of ATCO trailers strung together end-to-end and roofed over with sheets of plywood, and was about three quarters buried by drifting snow. 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. In the nearest outcrops 60 miles to the southeast in the Brooks Range, the Sadlerochit is hard dense sandstone, but at Prudhoe the bit penetrated porous sandstone and conglomerate.
And, even more 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. Inasmuch as there was no way of predicting with any level of confidence how thick this interval might be, drilling progressed slowly, we cut several cores, and wire-line logs were run in order to get a better idea of the reservoir quality of the sandstone and conglomerate.
Communication limited to radioIn the early stages of drilling at Prudhoe Bay, the only means of communication between the rig and the ARCO and Humble offices was by single side band HF radio - there were no telephones on this part of the North Slope and the nearest public telephone was at Barrow, 200 miles to the northwest.
The daily drilling reports and geological reports were transmitted to the ARCO office in Anchorage on an open radio frequency that anyone could listen in on. On a few occasions when the single sideband radio signals were out, a ham radio operator who had his ham set there in camp was sometimes able to contact someone on the ham network. In these cases, the daily drilling and geological reports were relayed to the ham radio operator on the other end, whoever and wherever he was, who then placed a collect phone call to the ARCO office in Anchorage to relay the reports.
Inasmuch as the radio link was often unreliable, company management gave the drilling and geological personnel on the rig a great amount of autonomy to proceed using their best judgment. This was a level of autonomy that is unheard of today in an era in which satellites enable continuous communication between remote rigs and the headquarters offices. But in 1967, the management folks in Anchorage and Los Angeles, where the Humble office was located, knew that if they did not receive a daily report from the rig, it was undoubtedly due to poor radio signals, and assumed that things were okay at the rig. They knew that if the rig personnel needed help or advice, they would be contacted somehow.
A thousand mile daily commuteBut after the well penetrated into the Sadlerochit Formation with its high gas readings in the drilling mud, it was obvious that things were getting more interesting by the day, and this sort of casual communication between rig and town came to a screeching halt.
Thus began a new daily routine. The first thing the geologists did in the morning was to update our sample logs and reports, and then picked up the daily drilling report from the tool pusher. Then one of us, usually me - leaving the ARCO geologist to monitor the drilling activity - hopped in the Interior Airways Beach Kingair that pilot Bob Jacobs was warming up.
Depending upon the weather, we flew to either Barrow or to Fairbanks to phone the reports in to the offices in Anchorage and Los Angeles. When we flew to Fairbanks, this was a daily commute of over a thousand miles to make two or three telephone calls, and I was usually back to the rig by early afternoon.
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 formation.
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, or DST. In the tests that I had witnessed in the past 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 (1.25 MMCF/D) 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.
Looks like gas discoveryBy 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.
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.
Although no wire-line logs were available for the lower part of the hole and the charts in the test tool could not be recovered, the test showed that 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. This was exciting, but oil, not gas, was the objective and the full significance of the discovery was going to have to await further drilling - and that was not going to occur until the fishing job was completed.
Clearly, there was going to be no need for geologists at the well site for some time, so I flew back to Anchorage and then on to the office in Los Angeles. The results of the DST were headline news in the Jan. 16 Anchorage Times.
Part 2 of this story will appear in the March 26 issue.
Editor’s note: Gil Mull submitted the above in March 2011, when it was first published by Petroleum News in a special publication, Exxon in Alaska.