Multi-component joint inversion for time-frequency electromagnetic (TFEM) method: A case study of igneous rock prospecting in western Sichuan

In recent years, non-seismic exploration has played a guiding role in the study of igneous rocks, deep-seated results, and fractures in western Sichuan, especially in the extraction and fine inversion of weak anomaly information by the time-frequency electromagnetic (TFEM) method, which has a good effect in searching for volcanic conduits and exploring the forming mechanism of volcanic rocks. However, the non-plane wave effect, sha-dow effect, and the additional effect of the artificial field source result in the multi-solutions to the data inversion, which leads to the low quality of inversion data imaging or even false anomalies. Multi-component electromagnetic data inversion is an effective method to overcome the difficulties mentioned above. On the basis of the principle of time-frequency electromagnetic exploration, the finite-difference forward modeling formula for the nine-point finite-difference structure of the two-dimensional model and three-dimensional source was derived. According to the principle of regularization inversion, a multi-component joint inversion objective function was constructed, and a multi-component joint inversion algorithm suitable for the time-frequency electromagnetic method was derived. To balance the difference in the order of magnitude between different components, we added the dynamic equilibrium coefficient to the inversion process. The theoretical model test results show that the multi-component joint inversion is more effective than single-component data inversion, and the noisy model test results indicate that the algorithm is correct and reliable and has great anti-noise performance. This method was applied to the observed time-frequency data from western Sichuan, and the inversion results were in good agreement with drilling information and other known information, which shows that the algorithm is practical and effective. © 2022, Editorial Department OIL GEOPHYSICAL PROSPECTING. All right reserved.