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From experimentation to manufacturing ConocoPhillips using new technologies, narrowing in on robust well design to produce West Sak heavy oil Kristen Nelson Petroleum News Editor-in-Chief
Heavy oil has been “the forgotten big resource in Alaska,” but after more than two decades of trying to get it right, North Slope producers are “narrowing in on a very robust design” for producing heavy oil, says ConocoPhillips Alaska’s Greg Leveille.
The 25 billion barrel heavy oil resource was discovered in the 1960s and 1970s, Leveille, manager of ConocoPhillips Alaska’s North Slope Greater Kuparuk satellites, said Feb. 19 at the annual Pacific Rim Construction Oil Mining Expo & Conference in Anchorage. Heavy oil on the North Slope includes the ConocoPhillips-operated West Sak accumulation at Kuparuk and the BP Exploration (Alaska)-operated Orion and Polaris accumulations at Prudhoe Bay and the Schrader Bluff accumulation at Milne Point.
The reason this heavy oil hasn’t been produced is because it doesn’t flow easily.
Think of the light oil accumulations as water, Leveille said: you can pour it easily and it flows readily into well bores, with production rates of 5,000 to 10,000 barrels a day.
The best heavy oil, at about 19 degrees American Petroleum Institute gravity, has “about the consistency of cold molasses,” he said, while heavier oil, at about 10 degrees API, is more like “warm peanut butter. And that’s what we’re trying to get out of the ground on the North Slope today.”
Because the flow rates for heavy oil are so low, “it’s been an economically very, very challenging opportunity to develop,” he said. First efforts in the 1980s Efforts to develop heavy oil began in the 1980s, with vertical wells and a “fracture stimulation technique to try to get the oil to move into those wells at a higher rate.” Although the companies were using the best science and technology available at the time, they only achieved production rates of a few hundred barrels per day, and with the cost of drilling the wells and fracture stimulating them, “that effort was not economic,” Leveille said.
Efforts were made again in the 1990s, but the results were the same: it just wasn’t economic.
But in 2000, “we started to employ some different technologies” to drill long lateral wells through producing zones. By drilling hundreds and then thousands of feet “of production lateral, we open up more of the rock to the well bore and that allows the oil to flow” from the reservoir more easily, he said.
In the 2000-2002 time frame, sand-exclusion screens were combined with medium-length laterals and the company got a “marginally economic result,” Leveille said. The sand-exclusion screens were an effort to control the formation, because in addition to being slow flowing, heavy oil occurs in formations that are not well consolidated — when oil flows, it brings solids with it. 2003 a transition year 2003 was “a big transition year for us,” Leveille said. “We took our moderate-length wells and we turned them into extremely long ones.” ConocoPhillips began drilling longer lateral sections through the reservoir, “we opened up all that reservoir rock … (and) for every foot of reservoir rock you open up you get that much more oil.”
Sand-exclusion screens were also replaced with a less expensive slotted liner, a “lower-cost type completion, ” he said.
With these changes, developing heavy oil became an economic proposition.
As part of its 2003 drilling, ConocoPhillips “set an Alaska record for 11,812 feet of section within the reservoir in a multilateral well,” opening more than two miles of reservoir to the well bore.
And production went from those few hundred barrels a day from vertical wells in the 1980s and 1990s, past production figures approaching a thousand barrels a day in 2000-2002, to numbers approaching 1,600 barrels a day in 2003. “What we’re doing with these wells is cutting the overall development cost and increasing the rate — which of course is good for the economics,” he said. Tri-lateral West Sak wells planned The plan in 2004 is to open even more reservoir to the well bore: tri-lateral wells are planned for West Sak in 2004, “which are going to have not two, but three laterals, and we’re going to have total distances which are in the three to four mile range instead of the 11,800-foot range. So we’re stretching these laterals longer and by doing that we’re hoping to increase the productivity of the wells.”
Heavy oil still only accounts for a small percentage of North Slope production, but the volume is growing. In mid-2003, Leveille said, the three North Slope heavy oil accumulations, in total, produced 30,000 to 35,000 barrels per day.
“Today it’s about 40,000 barrels of heavy oil being produced on the slope. And we expect that rate to grow significantly by year-end: we’ll certainly be above 50,000 barrels a day total production,” he said. Number of heavy oil wells expected to grow The trick with heavy oil, Leveille said, is to drill a lot of wells and “get up that learning curve very, very quickly,” and one way ConocoPhillips is doing that is by sharing information from its other heavy oil operations in Canada, Venezuela and China. The company is “involved with projects around the globe which have oil in place of over 100 billion barrels” of heavy oil, and has drilled hundreds of wells in the Orinoco heavy oil belt in Venezuela “that look very, very much like the wells we’re drilling here in Alaska.” The company is sending drilling engineers from Alaska to Venezuela to share what’s been learned in Alaska and pick up tips from those drilling in Venezuela.From experimentation to manufacturing What ConocoPhillips wants to do, Leveille said, “is to go from what I would call the experimentation phase — where we’ve been for the last several years in Alaska — to what I would describe as a manufacturing process.”
What’s an experimentation phase? “For the last several years … we’ve been drilling a lot of different types of wells. We’ve been testing lateral lengths; do we use slotted liners or screens to keep control of the formation?”
The company has tried “a lot of different variables.”
In 2004, “we’re narrowing in on a very robust design,” he said. “What we want to do now is to essentially start implementing that design time after time after time. Because that’s the way you get your costs down in this business, is by finding the best way to do something and then doing it over and over and over again.” What’s next? ConocoPhillips drilled eight heavy oil wells in 2003, “far more than we’ve drilled in the past,” Leveille said. The goal for 2004, he said, is to get approval for a much bigger program, including a number of projects. If those projects are approved, “we’re looking at drilling over 50 wells here in the next several years.
“But we’re going to try to transition here from this experimentation phase into a manufacturing phase … If you can do things over and over and over again, the costs tend to go down.”
Wells get drilled faster: West Sak is now at about 10 days per 10,000 feet, and the goal is to improve that in 2004, he said.
“By improving that efficiency, learning how to do things, we’re certainly able to access these resources in a much more economic manner.”
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