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.
