Stress-Induced Anisotropic Poroelasticity in Westerly Granite
Stress-Induced Anisotropic Poroelasticity in Westerly Granite
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西风花岗岩中应力引起的各向异性孔隙弹性
DOI：
10.1029/2023jb026909
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发表时间：
2023
期刊：
影响因子：
3.4
通讯作者：
Elsigood B
中科院分区：
文献类型：
--
作者：
Elsigood B
我们测量了三轴条件下，在高围压和一系列的差应力开裂花岗岩的孔隙弹性性质。斯开普顿系数和不排水杨氏模量和泊松比直接通过记录在轴向和径向应力的快速循环过程中的原位流体压力来确定。在超声频率下静态和动态测量排水性能。在一定的围压下，随着差应力的增加，岩石呈现出弹性横向各向同性，对称轴与压缩轴一致。Skempton系数也是各向异性的，孔隙压力响应于径向应力（coefficientBx）的变化比响应于轴向应力阶跃（Bz）的变化更大。Skempton系数的各向异性随着差应力的增加而增加，Bz减小，Bx略有增加。静态模量和Skempton系数的演变很好地近似Gassmann方程使用从超声测量获得的干模量。从动态数据反演的裂纹密度张量的基础上的Skempton系数的简化预测也表明可以接受的协议与直接观察。完美的定量协议没有达到，由于我们的动态测量，模型简化，和静态模量之间的固有差异，使用几个MPa的应力和动态超声应力振荡的应力步骤获得的不精确。
We measured poroelastic properties of cracked granite under triaxial conditions, at elevated confining pressure and a range of differential stresses. Skempton's coefficients and undrained Young's modulus and Poisson's ratio were determined directly by recording in situ fluid pressure during rapid cycles of axial and radial stress. Drained properties were measured both statically and dynamically at ultrasonic frequencies. At a given confining pressure, increasing differential stress leads to the development of elastically transverse isotropy, with symmetry axis aligned with the compression axis. Skempton's coefficients are also anisotropic, with larger changes in pore pressure in response to radial stress (coefficientBx) than to axial stress steps (Bz). The anisotropy in the Skempton coefficients increases with increasing differential stress, withBzdecreasing andBxslightly increasing. The evolution of static moduli and the Skempton coefficients is well approximated by Gassmann's equation using dry moduli obtained from ultrasonic measurements. Simplified predictions of the Skempton coefficients based on crack density tensors inverted from dynamic data also shows acceptable agreement with direct observations. Perfect quantitative agreement is not reached, due to the imprecision of our dynamic measurements, model simplifications, and inherent differences between static moduli obtained using stress steps of several MPa stress and dynamic ultrasonic stress oscillations.