The Barnett Shale is now the granddaddy of all of the North American shale plays, but that shouldn’t minimize its impact on the industry or on the continent’s ability to sustain natural gas production. Just a few short years ago pundits were decrying severe decline curves in Gulf of Mexico gas fields and wondering how the industry could ever replace those reserves. Meanwhile a handful of dedicated oil and service companies were attempting to answer that question in the Fort Worth Basin.
One who was along for the ride was Gary Schein, who spent almost 30 years engineering and designing fracturing treatments for BJ Services before moving to independent oil company Dale Resources LLC. Schein was part of a pioneering group that was willing to try, fail, and try again to get the right recipe for success in this challenging environment. The combination of technologies used today — horizontal drilling, multistage fracturing, slickwater fracs, and simultaneous fracs — are successful because of the years spent testing and perfecting the techniques.
Schein, who graduated from Northern Arizona University, said that most of these technologies were not really new. “Have people been doing multistage fracturing? Sure, we’ve been doing that for years,” he said. “Have there been slickwater fracs? There have been slickwater fracs for more than 50 years. It’s not like all of a sudden this is a new technology. This was really a new application of these technologies.”
He added that the first slickwater fracs in the Barnett shale were not a success. However, they were performed in vertical wells. The combination of the multizone fracs plus small mesh proppants in horizontal wells is what ultimately made the difference.
Schein is probably best known for pioneering the simultaneous fracture process, in which two adjacent wells are fracture-treated at the same time. The technology makes considerable sense — if a well is fractured and put on production, and then a nearby well is fractured later, the pressure drop from the producing well will pull the frac fluids toward that well, often killing it completely or resulting in depleted production.
“The goal of fracturing the Barnett, particularly in horizontal wells, is to expose as much shale to the well bore as possible to maximize production,” he said. “If you communicate with offset wells, you will minimize the amount of new rock that you expose to the well bore.
“But if you frac those wells at the same time, you can create some opposing pressure within the fracture system itself and create fractures in other parts of the shale, exposing more rock to both well bores.”
The numbers speak for themselves — at Dale and other independents that have tried the technique, these simultaneously fractured wells turn out to be some of the highest producers. In one Barnett case study, two wells were drilled from one pad, about 30 ft (10 m) apart, with roughly parallel trajectories ending about 1,000 ft (305 m) apart. The proximity of the wells suggested simultaneous fracturing to avoid killing either well. After treatment, both wells produced at significantly higher rates than nearby offsets.
Right now the challenge is to see how closely the well bores can be spaced before the technique stops working. If the procedure works as well in wells as close as 125 ft (38 m) apart as in wells 250 ft (76 m) apart, it could have a significant impact on expected ultimate recovery, Schein said. This process can also minimize the time to complete multiple wells on the same pad, improving well economics. There have been several instances of triple fracs on wells with improving well results as well.
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