1. College of Geology and Environment, Xi'an University of Science and Technology, Xi'an 710054, China 2. Exploration and Development Research Institute of PetroChina Qinghai Oilfield Company, Dunhuang 736202, China 3. Qinghai Provincial Key Laboratory of Plateau Saline-Lacustrine Basinal Oil & Gas Geology, Dunhuang 736202, China 4. Qinghai Branch of China Petroleum Logging Co., Ltd., Dunhuang 736202, China 5. College of Geology Engineering and Geomatics, Chang'an University, Shaanxi, Xi'an 710064, China
The static elastic parameters are crucial for shale oil and gas production and fracturing through water injection. Under stress effects, anisotropy exerts significant impacts on the dynamic and static elastic characteristics of shales. Investigating the dominant factors and mechanisms controlling reservoirs' dynamic and static elastic characteristics is a burning key scientific problem in shale oil and gas production and fracturing through water injection. Based on triaxial compression tests combining mechanics and acoustics for shales under different pressurization methods, this study delved into the impacts of anisotropy on the compressional/shear wave (P-and S-wave) velocities and macromechanical properties of shales, and the response patterns of dynamic and static elastic characteristics of shales. The results are as follows: (1) With an increase in the pressure, the dynamic and static Young's moduli of shales increase at a gradually decelerating rate, finally tending to be stable; (2) At certain bedding angles, the dynamic and static Young's moduli are positively correlated, with the former higher than the latter, whereas the dynamic and static Poisson's ratios manifest a subtle correlation; (3) The dynamic and static stiffness coefficients of shales increase with the confining pressure. The P-wave-related dynamic stiffness coefficients C11 and C33 display more significant changes than the S-wave-related dynamic stiffness coefficients C44 and C66; (4) The dynamic and static anisotropies of shales also increase with the confining pressure. The results of this study reveal the response mechanisms of the dynamic and static elastic characteristics of shales while providing crucial mechanical parameters for the exploitation and hydraulic fracturing of shale oil and gas reservoirs, thus demonstrating significant scientific research value.
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