Experimental investigation on mechanical characteristics of shale under water-rock interaction

Shale mechanical properties under water-rock interaction have a significant impact on wellbore stability, casing integrity, and hydraulic fracturing for shale oil and gas reservoirs. Most previous studies focused on the influence of fluid type and soaking time on shale mechanical properties, but the influence of soaking conditions (temperature and pressure) was seldom investigated. In order to investigate the influence of temperature, pressure, and soaking time on shale mechanical properties, the shale specimens were soaked under different temperatures and pressures, a large number of uniaxial compression experiments were carried out on the soaked shale specimens. The elastic modulus, Poisson's ratio, and peak strength of shale rock were selected as the response factors, and the second-order response surface model was employed to analyze the interaction relationship among mechanical properties and soaking conditions. The results indicated that the influence degree of a single factor on shale mechanical properties follows the order: soaking time > temperature > pressure. The response surface analysis results indicated that the influence degree of multi-factor interaction on shale mechanical properties follows the order: soaking time and temperature > soaking time and pressure > temperature and pressure, which confirmed that the interaction of soaking time and temperature has a significant impact on shale mechanical properties. The experimental results can help us better understand the evolution of shale mechanical properties under water-rock interaction, and it can also provide guidance for wellbore stability, casing integrity, and hydraulic fracturing for shale oil and gas exploitation.