A simulation study of the effect of clay swelling on fracture generation and porosity change in shales under stress anisotropy

The simulation study of the effect of clay swelling on fracture generation and porosity change in shale rocks is of great significance for applying hydraulic fracturing in the development of shale reservoirs in the petroleum industry. However, previous simulations did not consider the heterogeneous characteristics of shales. Besides, it is not clear how the swelling stresses are distributed owing to swelling inside shales. In this paper, we employ a discrete element method (DEM) modeling, which is combined with the CT images and MATLAB coding, to predict the effect of clay swelling on fracture generation and porosity change in shales under stress anisotropy. We are able to successfully simulate the effect of clay swelling on fracture generation and porosity change in heterogeneous shales under stress anisotropy by employing the discrete element method (DEM) modeling. Clay content is the key factor in fracture generation and the resulted porosity change. For shales with high clay content, clay swelling has contributions to the recovery of shale's porosity. The von Mises stress maps show that the stress inside the model is highly anisotropic and the maximum effective stresses concentrate on the fractures' areas. The larger the pressure is applied to the sample, the larger the von Mises stress can be observed. Stress anisotropy is a positive factor in fracture generation in the process of water-shale interaction. The degree of the clay swelling and the heterogeneity of samples are two factors that could influence the results.