Impacts of anisotropy on the dynamic and static elastic characteristics of shales under stress effects
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 fac-tors 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 correla-tion;(3)The dynamic and static stiffness coefficients of shales increase with the confining pressure.The P-wave-related dynamic stiff-ness 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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