As stated in The Plug and Perf Process, electric line and frac pump crews coordinate the pump-in process to convey each FP-setting tool-perforating gun “assembly” along the lateral section of the well – perhaps 70 times per well. High mechanical reliability is expected, so the pump-in process must also be reliable. But to achieve this, many process risks must be mitigated. How are some of these risks mitigated?
Run-in speed. An OEM specifies a maximum run-in speed for its FP in feet per minute (fpm). During conveyance, this is measured using electric line drum speed. Higher speeds increase the risk of FP damage. This is mitigated through electric line crew competency.
Excessive bypass flow. While dragging along the low side of the casing, a percentage of the pump-in flowrate always bypasses the assembly. But if assembly movement stops, the full flowrate bypasses it. An OEM usually states the bypass flowrate limit for its FP. Exceeding this limit increases the risk of FP damage. Mitigation is achieved through recognition and reaction, and coordination between the pumping crew and electric line crew.
Wellbore debris. Debris such as frac sand and metallic perforating gun remnants increase the risk of FP failure. Accumulations of debris can stop movement of the assembly, leading to excessive bypass flow. If embedded in the FP, debris can prevent it from gripping and/or sealing within the casing. Mitigation is achieved through practices that promote a clean wellbore.
Distressed frac plug. When a FP is moving at 4 ½ mph through the lateral, timely recognition and reaction to a problem is crucial. Once recognized, fast reaction can mitigate against 2nd order risks. However, recognition and reaction risks are primarily a human factors challenge. Mitigation can be achieved through experience, competency, job planning, and coordination.
Successfully pumping a FP assembly to its target location requires mitigation of process risks. These risks can be mitigated only if known. The pump-in process will vary from well to well but can be de-risked in advance using process Failure Modes and Effects Analysis (pFMEA).
TRUTH: Frac plug reliability is highly influenced by pump-in process reliability.
This is the 4th in a series of five articles on why Frac Plugs fail in Plug and Perf applications.
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