Electrical structure identification of deep shale gas reservoir in complex structural area using wide field electromagnetic method

To fully exploit the technical advantages of the large-depth and high-precision artificial source electromagnetic method in the complex structure area of southern Sichuan and compensate for the shortcomings of the conventional electromagnetic method in exploration depth, precision, and accuracy, the large-depth and high-precision wide field electromagnetic method is applied to the complex structure test area of the Luochang syncline and Yuhe nose anticline in the southern Sichuan. The advantages of the wide field electromagnetic method in detecting deep, low-resistivity thin layers are demonstrated. First, on the basis of the analysis of physical property data, a geological–geoelectric model is established in the test area, and the wide field electromagnetic method is numerically simulated to analyze and evaluate the response characteristics of deep thin shale gas layers on wide field electromagnetic curves. Second, a wide field electromagnetic test is conducted in the complex structure area of southern Sichuan. After data processing and inversion imaging, apparent resistivity logging data are used for calibration to develop an apparent resistivity interpretation model suitable for the test area. On the basis of the results, the characteristics of the electrical structure change in the shallow longitudinal formation of 6 km are implemented, and the transverse electrical distribution characteristics of the deep shale gas layer are delineated. In the prediction area near the well, the subsequent data verification shows that the apparent resistivity obtained using the inversion of the wide field electromagnetic method is consistent with the trend of apparent resistivity revealed by logging, which proves that this method can effectively identify the weak response characteristics of deep shale gas formations in complex structural areas. This experiment, it is shown shows that the wide field electromagnetic method with a large depth and high precision can effectively characterize the electrical characteristics of deep, low-resistivity thin layers in complex structural areas, and a new set of low-cost evaluation technologies for shale gas target layers based on the wide field electromagnetic method is explored.