Calculation of reservoir fracture network propagation based on lightning breakdown path simulation

Abstract

<p indent="0mm">Hydraulic fracturing produces fractures with high conductivity and forms a complex fracture network, which supports the economic development of unconventional reservoirs. Describing a fracture network is the basic premise for fracturing evaluation and production simulation. This study analyzes the lightning breakdown path simulation method and adopts the principle of similarity to comprehensively consider the reservoir geological parameters, <italic>in situ</italic> stress distribution, and fracturing construction parameters; the results are used to develop a new fracture simulation method. In the proposed method, circumferential stress and critical fracture stress are used to determine the extension range of secondary fractures, and random function and fractal probability index are introduced to characterize the random distribution of the fracture extension. Then, an actual production well fracture network with microseismic monitoring data is simulated. The results show that the proposed simulation method can accurately describe the fracture network with a high degree of matching in the range covered by the microseismic data. In addition, the influences of the <italic>in situ</italic> stress difference gradient, initial injection pressure, and fractal probability index on the fracture morphology are analyzed. This research shows that a smaller <italic>in situ</italic> stress difference gradient relates to greater fracturing fluid injection pressure and smaller fractal probability index and fracturing fluid viscosity, which facilitates the formation of more branch fracture network systems. Finally, the proposed method is applied to the simulation of a fracture network in two wells. The results show that the inverted fracture morphology is consistent with the distribution range of microseismic data. The simulation of 94 clusters of fractures in 32 sections of well X2 shows that the fracture branches of the well are obviously developed, which indicates a generally complex fracture network. The transverse communication of the single wing fracture network is about <sc>200 m,</sc> and the longitudinal communication is about <sc>20 m.</sc> Therefore, the calculation method of fracture network propagation based on lightning simulation can consider the uncertainty in the fracture propagation direction, particularly when the reservoir geological characteristics are unclear. Moreover, it provides a new method for simulating hydraulic fracture propagation.