Analysis of the transient pressure of fractured wells coupling with irregular flow fracture: Semi-analytical model and case study

Abstract

A strange phenomenon happens all the time that the obtained permeability by the conventional finite-conductivity model (FC) is much larger than the actual value in tight reservoir. The conventional pressure-transient analysis models of vertical-fractured wells regard fracture as a regularly non-uniform flow rate. However, due to fracture bending, irregular proppant filling, proppant crushing, and inadequate fracturing fluid backflowing, the fracture may show an irregular flow rate in different fracture segments. An additional horizontal line or concave curve appears on the pressure derivative curve by considering the irregular flow rate in the fracture. In the past, the concave curve would be regarded as an error from field data, and the horizontal line on the pressure derivative curve would be regarded as the quasi-radial flow regime. If the horizontal line is recognized as the quasi-radial flow regime in tight reservoir, the interpreted permeability will be magnified many times. In this work, we proposed a multi-segment irregular non-uniform flow model with changing wellbore storage effect (MINFC) to characterize the pressure response of irregular fractures better, making the pressure response in the fracture more realistic. The MINFC model can correct the magnified permeability and diagnose the partial closure fracture location, length, and flow rate. Green function and Newman product method are applied to obtain the bottom-hole pressure behavior. The results demonstrate that the pressure derivative curve is not a line with a slope of 0.5 in the irregular fracture flow regime but a horizontal or concave curve. Sensitivity analysis demonstrates that the location and length of the irregular proppant filling will affect the duration of the horizontal line. In conclusion, the reservoir permeability and fracture half-length obtained by the MINFC model are closer to the actual value. The locations of irregular proppant filling and low flow rete are quantified so that researchers can take steps to improve fracture performance. Finally, the comparison between the MINFC model and the finite-conductivity model verifies the MINFC model's accuracy. The MINFC model matches field data to verify its practicability.