Development of the coupled elastoplastic damage constitutional model of acidized shale gas formation based on experimental study

Since the focus of shale reservoir exploration and exploitation have shifted to deeply buried formations, the high breakdown pressure becomes an obstacle for massive hydraulic fracturing. Pre-acidizing is an effective way to reduce the breakdown pressure, at the same time it causes the plastic deformation that affects the shale fracability. In order to evaluate the acidizing effect on rock mechanical deformation, experimental and numerical approaches were conducted in this paper. A series of experimental studies on the effects of hydrochloric acid on the micro-structure and rock mechanical properties of shale samples was conducted for analyzing the mechanism of acidizing. A damage elastoplastic constitutive model for acidized shale was proposed to simulate the nonlinear deformation and damage process caused by the acidizing effect and pressure. The model input parameters were interpreted from the experimental data. This constitutive model based on plastic mechanics and damage mechanics was verified through good correlation between the numerical simulation results and the experimental data. This model is practical because its parameters are easy to acquire from the conventional indoor experimental data and it could be embedded into the hydraulic fracturing model conveniently.