Paul Weddle describes himself as a “perforation geek.” The completion manager for Liberty Resources is among a small group that has an obsessive interest in all the details that can alter the performance of the openings blasted through casing, cement, and into rock during hydraulic fracturing.
The shaped charges that create circular openings with amazing force are a well-established technology that gets little notice so long as the guns go off as planned. But Weddle is among a few who see perforations as the point of attack for raising fracturing performance.
At the recent SPE Hydraulic Fracturing Technology Conference, Liberty reported completions in North Dakota that routinely stimulated more than 12 of 15 clusters, resulting in wells producing 1.7 to 2.5 times more than comparable wells (SPE 189880). By changing the way perforations were used, the operator was able to reduce the number of stages to 27 along a 9,500-ft lateral, which it estimates saved 15% on its finding and developing costs per barrel.
It stimulated those stages, which are about 350 ft long, with 15 clusters of perforations, with two perforations in each. This represents a significant break from the standard design of four or five clusters each with as many as six perforations. Since the tests reported in the paper, Weddle said Liberty has “gone all in on it.”
ConocoPhillips is working on designs with as many as 10 clusters per stage and two or three perforations per cluster, with all of them located at the top of casing, said Dave Cramer, a senior engineering fellow in completions for ConocoPhillips.
More clusters per stage allow operators to fracture longer wells without the cost of added stages, but Liberty and ConocoPhillips have not had a lot of company.
“I would say these ideas are not yet common to the industry, but at least a few operators and service companies are thinking about them,” said Robert Barree, president of Barree & Associates. The fracturing consultant said that “15 clusters are a lot. Most people are at the five to eight level … and some are at three.”
Grouping clusters with many perforations would seem to offer safety in numbers. The hard part about what is new is the old problem of directing a sufficiently strong stream of water into many small holes spread out along a long horizontal wellbore. Tight clusters of perforations can add stress that can interfere with fracture growth.
Liberty’s method depends on its ability to limit the fluid into each of the perforations to ensure that the high-pressure flow is distributed equally enough to stimulate most of the perforations. Liberty’s new method, called eXtreme Limited Entry (XLE), is based on work going back decades, including a paper in 1987 by Cramer (SPE 16189) on limited entry fracturing.