Mikhaltsevitch Vassily, Lebedev Maxim
Centre for Exploration Geophysics, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.
Centre for Sustainable Energy and Resources, Edith Cowan University, 270 Joondalup Dr, Joondalup, WA 6027, Australia.
Sensors (Basel). 2024 Feb 8;24(4):1122. doi: 10.3390/s24041122.
Numerous experimental and theoretical studies undertaken to determine the effective stress coefficient for seismic velocities in rocks stem from the importance of this geomechanical parameter both for monitoring changes in rock saturation and pore pressure distribution in connection with reservoir production, and for overpressure prediction in reservoirs and formations from seismic data. The present work pursues a task to determine, in the framework of a low-frequency laboratory study, the dependence of the elastic moduli of n-decane-saturated sandstone on the relationship between pore and confining pressures. The study was conducted on a sandstone sample with high quartz and notable clay content in a quasi-static regime when a 100 mL tank filled with n-decane was directly connected to the pore space of the sample. The measurements were carried out at a seismic frequency of 2 Hz and strains, controlled by semiconductor strain gauges, not exceeding 10. The study was performed using a forced-oscillation laboratory apparatus utilizing the stress-strain relationship. The dynamic elastic moduli were measured in two sets of experiments: at constant pore pressures of 0, 1, and 5 MPa and differential pressure (defined as a difference between confining and pore pressures) that varied from 3 to 19 MPa; and at a constant confining pressure of 20 MPa and pore pressure that varied from 1 to 17 MP. It was shown that the elastic moduli obtained in the measurements were in good agreement with the Gassmann moduli calculated for the range of differential pressures used in our experiments, which corresponds to the effective stress coefficient equal to unity.
为确定岩石地震波速度的有效应力系数而进行的大量实验和理论研究，源于这一地质力学参数对于监测与油藏开采相关的岩石饱和度和孔隙压力分布变化，以及根据地震数据预测油藏和地层超压的重要性。本研究旨在通过低频实验室研究，确定正癸烷饱和砂岩的弹性模量与孔隙压力和围压之间关系的依赖情况。研究是在一个石英含量高且粘土含量显著的砂岩样品上进行的，处于准静态状态，此时一个装有100毫升正癸烷的容器直接与样品的孔隙空间相连。测量在2赫兹的地震频率下进行，应变由半导体应变片控制，不超过10。研究使用了利用应力 - 应变关系的强迫振荡实验室装置。动态弹性模量在两组实验中进行测量：一组实验中孔隙压力恒定为0、1和5兆帕，围压与孔隙压力之差（定义为围压与孔隙压力之差）从3变化到19兆帕；另一组实验中围压恒定为20兆帕，孔隙压力从1变化到17兆帕。结果表明，测量得到的弹性模量与根据我们实验中使用的围压差值范围计算出的加斯曼模量吻合良好，这对应于有效应力系数等于1。
