The experimental investigation of effect of supercritical CO2 immersion on mechanical properties and pore structure of shale

Abstract

The interactions between supercritical carbon dioxide (ScCO2) and shale significantly affect shale reservoir exploitation. This study investigates the effect of ScCO2 immersion on the mechanical behavior and microstructure of shale with inclined layering. The orientations α of the bedding plane with respect to the horizontal direction are 0°, 30°, 45°, 60°, and 90°. Mechanical experiment results indicated that the compressive strength of shale decreased, while the elastic moduli increased in ScCO2 immersion. The compressive strength exhibited the same variation tendency, while the elastic modulus exhibited the opposite change trend with increasing α before and in ScCO2 immersion. ScCO2 alters the mechanical properties of shale through pressure, adsorption, and dissolution; the dominant factor enhancing the elastic modulus is adsorption. X-ray diffraction and low-pressure nitrogen adsorption experiments showed that the influence of ScCO2 on the microstructure of the layering was more significant than the influence on the matrix; ScCO2 mainly broadened the micropores in the matrix, while transforming the mesopores and macropores in the bedding plane. This study provides the theoretical basis for the development of shale reservoirs using ScCO2.