The effect of heterogeneity on hydraulic fracturing in shale

Modelling hydraulic fracturing processes in shale oil and gas development remains a major challenge for industrial applications. The omission of heterogeneity inherent in the shale matrix may be one of the causes for the divergence between simulated fractures and those in reality. To elucidate the effects of heterogeneity on hydraulic fracturing, a workflow is developed for generating heterogeneous fields of hydraulic and geomechanical properties based on relatively easily available compressional wave velocity and shear wave velocity. After that, the workflow is implemented in our thermo-hydro-mechanical simulator for hydraulic fracturing. With the integrated simulator, the following are investigated: the effect of heterogeneity and the interactive effects of heterogeneity with other factors, i.e., in-situ stress gradient and stress shadow, the significance of different levels of heterogeneity, and the impact of various injection rates. The simulation results showed that these factors could have either synergetic or competitive effects under different circumstances. Also, different levels of heterogeneity result in different patterns of fractures' geometry. According to our study, a heterogeneity field with a large coefficient of variation (CV) and medium correlation length (CL) turns out to develop fractures of the most complex patterns. Moreover, the high injection rate leads to neutralization of the influence of heterogeneity through the averaging effect of intense fracturing. The study leads to better understandings in the mechanism of hydraulic fracturing process under complicated factors such as heterogeneity, interactive effects, fracturing strategies, and both modes of rock failure. This study may shed light on future research on hydraulic fracturing and possible applications in practice as well as some improvements in designing hydraulic fracturing simulator.