Evolving Perforation Strategies Improve Fracture Performance

Abstract

Abstract

Tight control of hole size, orientation, and pressure can yield more productive hydraulic fractures. Hydraulic-fracturing technologies and methods for unconventional reservoirs have evolved over time. SPE 230643 compiles key insights from notable SPE papers along with the authors’ experiences into a set of completions best practices covering limited-entry perforating, perforation-cluster spacing and density, and oriented perforating within the plug-and-perf process, which creates fractures along the lateral to connect the wellbore with the reservoir rock. Dave Cramer, retired from his post of senior engineering fellow at ConocoPhillips, said during the SPE Hydraulic Fracturing Technology Conference and Exhibition in February that entry-hole friction of the perf will affect treatment effectiveness and that the Bernoulli equation, which predicts pressure drop through an orifice, is useful for evaluating perforation friction, which creates a backpressure within the wellbore. The characteristics of the entry hole differ depending on how the perforation is created. “In the old days we had bullets at our disposal” to punch through the pipe into the formation, he said, noting that method yielded “a lot better uniformity.” He added that there has been recent work to resurrect the use of bullets for perforating, he said. Now, jets of high-pressure gas are used to punch the perforation hole. “Every one of these perforations is a little bit different than the other. So, there’s going to be some inherent variability in diameter,” resulting in variable flow rates among the perforations for a given pressure drop, Cramer said. It’s possible to improve accuracy and consistency with jet perfs, he said. Gun clearance contributes to hole-diameter variability. “Having a consistent gun clearance is going to give you more consistent hole diameters.” Other factors include the charge itself, how it fits, how much metal it must penetrate, and the orientation, he said (Fig. 1). “The more precise you are with all these aspects, and using fresh charges from the same lot, the more uniform your hole diameter is going to be.” And that’s important because it will reduce variations in flow rate among perforations and perforation clusters, which leads to improved uniformity of treatments, the authors wrote. ConocoPhillips tested oriented perforations in Poland in 2011 and tested oriented vs. nonoriented perforations in the Eagle Ford in 2016. Cramer said that in the Eagle Ford, the operator had perforations pointing straight up (zero-degree phasing) in 35 wells, and in 64 wells used nonoriented 120° phasing with the same number of perforations. A later review of the program found “across the board in all the different areas that the oriented perf rating was superior in production results to nonoriented perf rating,” yielding about 13% better production, he said, citing SPE 204203. “Oriented perforating; it’s made a big difference in our outcomes.” A 2019 finding concluded entry holes oriented to the high side delivered a more regular outcome than nonoriented holes (SPE 194334), he said. “We had so much better productivity with the oriented perforated (holes). Definitely a best practice” that reduces runaway perfs, or excessively enlarged holes due to erosion. He added that self-orienting guns delivered better, tighter results (Fig. 2).