Propagation Simulation and Structural Characterization of Multiple Hydraulic Fractures in Naturally Fractured Unconventional Hydrocarbon Reservoirs

Abstract Multiple hydraulic fractures in naturally fractured unconventional hydrocarbon reservoirs often induce complex fracture network growth, as revealed by microseismic monitoring data from Maxwell et al. (2002), Fisher et al. (2005) and Daniels et al. (2007). History matching and production forecasting from an unconventional hydrocarbon reservoir are possible only if a complex fracture network can be clearly described through the engineering parameters. However, the current integrated technology of propagation simulation and structural characterization of a complex fracture network still presents extreme challenges. A new propagation modeling and characterization technique has been developed for complex fracture network expansion that combines the improved displacement discontinuity method (DDM) and pseudo-3D fracture propagation model to simulate the propagation process of complex fracture networks and increase stimulation accuracy. These improvements are very important for modeling and simulation of multifracture propagation in an unconventional hydrocarbon reservoir with natural fractures. The theoretical model includes the calculation model of the combined stress field, the mechanical model of fracture propagation patterns and corresponding propagation criteria, the injection fluid distribution model, and the mathematical model for structural description and morphological characterization as a postprocessing program. The propagation simulation results for a complex fracture network are implicitly and directly entered into the postprocessing program and further characterized by some engineering parameters. Simulation results show that different fracture network propagation patterns are produced, which are governed by the in situ stress anisotropy, hydraulic fracture density, and distribution modes of pre-existing natural fractures as well as the fracture interaction angle. More importantly, the simulation results can be characterized by different engineering parameters. The presented comprehensive workflow could assist reservoir engineers in clearly understanding and evaluating complex fracture networks, including the geometric morphology, spatial distribution and conductivity of complex fracture networks. This technique can help identify stimulation and forecasting strategies that will significantly improve well performance and ultimate recovery from unconventional hydrocarbon reservoirs.