Numerical simulation of two-dimensional cyclic water injection in rock fractures

Abstract

Abstract Understanding the shear-seepage behaviors in rock fractures is crucial in excavation of tunnels through fractured surrounding rocks and mining explorations, however, the cyclic injection mechanism of fractures is not yet fully understood. This study utilized the COMSOL Multiphysics software to simulate the cyclic water injection in rock fractures with various injection amplitudes and frequencies. We documented that when subjected to cyclic water injection, the fluid flow in the rock fractures exhibited periodic fluctuations. As water injection amplitude increases, the flow pattern within the low-flow region become more turbulent, creating significant disturbances to the overall flow pattern. Additionally, the permeability of rock fractures varies periodically with the inlet flow rate, resulting in a permeability-flow rate relationship that forms an elliptical closed curve over time. Moreover, the amplitude of fluctuation in permeability increases as the water injection frequency and amplitude increase, illustrating that water injection within a specific range could enhance permeability in rock fractures. Furthermore, we proposed an approach to identify and quantify the primary channel and eddy flow areas.