Numerical simulation and transient electromagnetic response characteristics of fracturing-induced fractures in underground shale formations

Hydraulic fracturing is currently one of the most important techniques for enhancing oilfield production, with the primary objective of transforming shale formations to generate artificial fractures. Understanding the development process, depth, length characteristics, and distribution of these fracturing-induced fractures is crucial for the efficient exploitation of shale formations and the improvement of production capacity. In practical engineering applications, surface-based electromagnetic methods are significantly limited by detection depth and accuracy. To enhance the efficiency and accuracy of inter-well detection, it is feasible to conduct simultaneous observations from both downhole well patterns and surface arrays. The influence of various shale formation parameters in vertical wells on measurement results was investigated. By utilizing the principles of transient electromagnetic (TEM) methods, a grounded electric dipole source was employed to transmit signals. Hydraulic fracturing was carried out at one or multiple locations along the inner wall of the well casing, with surface fracturing equipment used to compress the sandstone around the shale, thus inducing fractures. A saline electrolyte was then injected, creating low-resistivity fractures around the wellbore. This resulted in a vertically distributed geological model with varying conductivity due to the injected fracturing fluid. Geoelectric data was acquired through a surface concentric circular array composed of three loops, with a total of 72 measurement points arranged along the loops, enabling the monitoring of the development of underground fracturing-induced fractures. Based on finite element numerical simulations conducted using COMSOL Multiphysics software, the response characteristics of fractures with different geometries in shale formations were analyzed. The results demonstrate that this method effectively determines the orientation, burial depth, and length of subsurface fractures, thereby providing a theoretical foundation and technical approach for the characterization of fracturing-induced low-resistivity fractures in subsurface formations.