Summary Fracture-closure pressure is an important parameter for fracture treatment design and evaluation. The pump-in/flowback (PIFB) test is frequently used to estimate its magnitude. The test is attractive because bottomhole pressures (BHP's) during flowback develop a distinct and repeatable signature. This is in contrast to the pump-in/ shut-in test, where strong indications of fracture closure are rarely seen. Various techniques are used to extract closure pressure from the flowback-pressure response. Unfortunately, these techniques give different estimates for closure pressure, and their theoretical bases are not well established. We present results that place the PIFB test on a firmer foundation. A numerical model is used to simulate the PIFB test and glean physical mechanisms contributing to the response. On the basis of our simulation results, we propose interpretation techniques that give better estimates of closure pressure than existing techniques.
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Plahn et al. (1997) studied this question.
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