Experiment on mechanical properties of shale soaked with supercritical carbon dioxide

Key words:  supercritical carbon dioxide  shale  carbon dioxide soaking  mechanical properties  rock mechanics

Abstract:

Supercritical carbon dioxide as fracturing or displacement fluid has great potential in exploration and development of unconventional reservoirs such as shale oil and gas. In this study, the mechanical properties of shale rocks soaked with carbon dioxide soaking were investigated via indoor experiments under different pressure and temperature conditions. The experimental results show that the shale rock core expanded in the beginning of the soaking, then contracted, and finally leveled off. Its elastic modulus and Poisson 's ratio increased after the soaking. At near the critical pressure of CO₂, the mechanical property of the core changes sharply, and then it becomes stable as pressure further increases. The average increments of the elastic modulus and the Poisson 's ratio are of 43.4% and 36.6%, respectively. With the increase of temperature, the elastic modulus and Poisson 's ratio increases gradually, and the maximum increase for the two parameters is of 138.4% and 24.7% respectively. The change of the mechanical properties of shale is not very sensitive to CO₂ pressure, but the influence of temperature is obvious and complex. A quantitative description of the mechanical parameters of shale rocks soaking in CO₂ under high temperature and pressure conditions was given, which can provide guidelines for the application of supercritical carbon dioxide in shale gas exploitation in terms of rock mechanics.