时移电阻率法三维反演研究

3D Time-lapse resistivity inversion

时移电阻率法是监测浅地表物性参数动态变化的有效方法之一.在实际应用中,由于观测噪声随时间变化,基于不同时刻观测数据单独反演所得的电性结构变化可能存在虚假信息.这些时变噪声引起的虚假信息增加了时移电阻率法解释的难度.本文通过在传统的正则化反演目标函数中增加时移约束来调控相邻时刻同一位置的电性差异,以抑制时变噪声产生的虚假变化.在此基础上,采用有限内存拟牛顿法实现了时移电阻率法三维反演.合成数据反演结果表明,相对于不同时刻监测数据单独反演的结果,时移反演可更好的抑制噪声影响,获取更准确的电性结构及其动态变化.野外实验数据反演结果表明,时移反演能更真实刻画实验区域的电性结构变化.上述结果表明,时移反演可以更好的压制由背景噪声引起的假异常,提高反演结果的准确性和解释的可靠性.本研究为时移电阻率法监测浅地表电性结构动态变化提供了一种有效途径.

Time-lapse resistivity imaging is one of the effective approaches for monitoring dynamic conductivity changes in shallow subsurface. In practice, due to temporal variations in observation noise, electrical structural changes derived from individual inversions may contain false information, increasing the difficulty in interpreting the time-lapse resistivity results. In this study, the time-lapse constraint is applied to the traditional regularized inversion objective function to control the electrical difference at adjacent time points, thereby suppressing the spurious changes caused by time-varying noise. The three-dimensional (3D) time-lapse resistivity inversion approach is then realized by using the limited memory quasi-Newton method. The inversion results of synthetic data show that, compared with the results of individual inversion, time-lapse method can better suppress the influence of noise and obtain more accurate electrical structure changes. Field experiments show that time-lapse inversion can more closely reveal the actual electrical structure changes. These results suggest that time-lapse inversion can suppress false anomalies caused by background noise and improve the accuracy of inversion results. This study provides an effective way to monitor the dynamic changes of electrical structure in shallow subsurface.