The distinct element analysis for hydraulic fracturing in hard rock considering fluid viscosity and particle size distribution

A series of simulations for hydraulic fracturing in competent rock was performed by using the flow-coupled DEM code to discuss the influence of the fluid viscosity and the particle size distribution. The simulation results show good agreement with experimental results that contain the AE measurement data. The following observations can be made. When a low viscosity fluid is used, the fluid infiltrates into the fracture immediately. On the other hand, when a high viscosity fluid is used, the fluid infiltrates slowly into the crack after the fracture first elongates. Although tensile cracks are dominantly generated in the simulation, the energy released from a tensile crack becomes small because the tensile strength of rock is obviously small compared with the compressive strength. Such a small AE is easily buried in a noise and difficult to be measured in an experiment. Therefore, in AE measurement experiment, shear type AE with large energy is dominantly observed, as many previous researches have indicated.

► Hydraulic fracturing in hard rock was simulated by using the flow-coupled DEM.
► Crack initiation and breakdown pressure for the low viscosity fluid became low.
► Breakdown pressure in case of using a homogeneous model was remarkably high.
► Shear AE is dominant in an experiment because energy of shear crack is large.