North Slope producers are enhancing production from tight-rock formations with multi-stage hydraulic fracturing, and it’s a process that could unlock large new oil and gas resources, the companies say.
Companies have done fracturing of wells on the Slope, and in Cook Inlet, for decades. The multi-stage “frack” jobs are larger, however, although not on the scale done in the Lower 48 shale plays.
Caelus Energy has using the process for some time and has been able to boost wells initial rates from about 2,000 barrels per day to 6,000 bpd to 7,000 bpd at its Oooguruk field after fracturing, according to the company’s Alaska vice president, Pat Foley. The Oooguruk well results were published in a Society of Petroleum Engineers paper and presented in a conference in Houston in late 2015.
Caelus sees the technique as a breakthrough technology in unlocking large resources locked in tight rock that have been bypassed by other companies.
BP Exploration Alaska is meanwhile also experimenting with the technique in the Lisburne field, a tight limestone formation that underlies the main Prudhoe Bay reservoir. The company has also achieved good results, company spokeswoman Dawn Patience said.
Lisburne wells have been notoriously poor producers, averaging about 250 bpd.
Last year, however, BP drilled three new horizontal production wells and applied multi-stage fracturing, resulting in a boost of output for the three wells combined to 3,500 bpd, according to BP reservoir engineer Joshua J. Michie, a member of BP’s Lisburne development team.
The Lisburne well results have just been published in a Society of Petroleum Engineers paper, with Michie as one of the authors.
Slope fracturing smaller in scale
The North Slope hydraulic fracturing so far is smaller in scale than fracturing being done in the Bakken and Eagleford shale oil plays of the Lower 48 states.
Companies are exploring shale formations on the Slope, however, but so far no production tests have been done.
The three tight-rock Lisburne wells exceeded BP’s expectations by about a third but have since declined to about 2,500 bpd. However, Caelus’ wells at Oooguruk stimulated with multi-stage fracturing have not shown significant declines so far, Foley said are often choked to 2,000 bpd to 4,000 bpd early in their life to maximize reservoir performance. Production rates fall to roughly one third of the initial rate one year after they are brought on production.
Foley said Caelus typically drills four or five new wells each year and fracture stimulates them in a single winter program winter at Oooguruk’s offshore gravel production island, which is in shallow Beaufort Sea waters near shore, he said.
When the drilling is complete the company mobilizes equipment for the fracturing of all of the new wells, Foley said. That has just been completed on five new wells drilled at Oooguruk and the production benefit so far has been to lift the field’s production from about 15,000 bpd prior to the fracturing to about 18,000 bpd with four of the new wells on line.
When the last newly-fractured well is put on line Oooguruk’s production will be 20,000 bpd, Foley said.
Fracturing adds to Oooguruk costs
Caelus injected about 2.5 million pounds of ceramic proppant and water based fracturing fluids per well in its Oooguruk multi-stage fracturing. Costs for a new Oooguruk production well average about $20 million and the multi-stage fracturing adds about $10 million to costs, Foley said.
In its Lisburne wells BP used about 30,000 pounds of proppant and 1,000 barrels of fluids in each stage of fracturing, with four stages of fracturing applied at one well and five stages in a second well.
“The important aspect was not so much their size as a focus on stimulating the poorer intervals along the well’s path,” Michie said. BP gave no figures on the cost of the drilling and stimulations.
Tight rock at Lisburne
Lisburne has been a poster child for unpleasant production performance for the North Slope. The reservoir has tight limestone rock with poor permeability but also with a highly complex fracture network.
Oil can flow a hundred times more easily in the Ivishak reservoir, the main Prudhoe Bay producing formation, than it does in the Lisburne, BP has said in a briefing paper.
Initial development began in 1985 but was stopped in 1991 due to poor performance. ARCO Alaska was the operator of the eastern side of Prudhoe Bay, which included Lisburne. After ARCO was acquired by BP the development of Lisburne resumed from 2003 to 2006 but with less-expensive coiled-tubing drilling. The results were equally poor.
While recovery of oil is estimated at 50 percent of 26 billion barrels of oil-in-place in the Ivishak it is only 7 percent of 2.5 billion barrels of oil-in-place in the Lisburne.
If BP engineers can figure ways to get more oil out of the Lisburne rock, such as expanded use of hydraulic fracturing, it would be a big win for the company.
