Multiple hydraulic fractures in naturally fractured unconventional oil reservoirs have often induced complex fracture network growth, as revealed by microseismic monitoring data by Maxwell et al. (2002), Fisher et al. (2005) and Daniels et al. (2007). History matching and production forecasting from an unconventional oil reservoir is possible only if a complex fracture network can be clearly described through the engineering parameters. However, currently, the integration technology of propagation simulation and structural characterization of the complex fracture network is still an extreme challenge.
A new propagation modeling and characterization technique has been developed for these complex fracture network expansion that combines improved displacement discontinuity method (DDM) and pseudo-3D fracture propagation model to simulate the propagation process of complex fracture network and improve stimulation accuracy. This is very important for modeling and simulation of multi-fracture propagation in a unconventional oil reservoir with natural fractures. The theoretical model include the calculation model of combined stress field, the mechanical model of fracture propagation patterns and the corresponding propagation criteria, the injection fluid distribution model, and the mathematical model for structural description and morphological characterization as a post-processing program. The propagation simulation results of complex fracture network are implicitly and directly entered into the post-processing program and characterized by some engineering parameters as well.
Simulation results show that the different propagation patterns of fracture network are produced, which is governed by the in-situ stress anisotropy, hydraulic fracture density, and distribution modes of pre-existing natural fracture as well as fractures interaction angle. More importantly, the simulation results can be characterized as different engineering parameters containing the fracture network bandlength, bandwidth, stimulated reservoir area (SRA) and fracture width. The presented comprehensive workflow could assists the reservoir engineers in clearly understanding and evaluating the complex fracture network, including geometrical morphology, spatial distribution, and conductivity of complex fracture networks.
The propagation simulation and structural characterization technique presented in this paper can help identify stimulation and forecasting strategies that will significantly improve well performance and ultimate recovery from an unconventional oil reservoir.