Numerical investigation of laboratory hydraulic fracturing tests in Pocheon granite

This study investigates numerically several hydraulic fracturing experiments that were performed on intact cubic Pocheon granite samples applying different injection protocols. The goal of the laboratory experiments is to test the concept of cyclic soft stimulation which aims to increase permeability sustainably among others. The Irazu 2D numerical code is used to simulate explicitly coupled hydraulic diffusion and fracturing processes under bi-axial stress conditions. Using the hybrid finite-discrete element modelling approach, we test two injection schemes, constant-rate continuous injection and cyclic progressive injection on homogeneous and heterogeneous samples. Our study focuses on the connection between the geometry of hydraulic fractures, fracturing mechanisms and the permeability increase after injection. The models capture several characteristics of the hydraulic fracturing tests using a time-scaling approach. The numerical simulation results show good agreement with the laboratory experiments in terms of pressure evolution characteristics and fracture pattern. Based on the simulation results, the constant-rate continuous and cyclic progressive injection schemes applied to heterogeneous rock sample with pre-existing fractures show the highest hydraulic aperture increase, and thus permeability enhancement.