3-D Numerical Modeling of Transient Electromagnetic Responses in Anisotropic Formation With Cement-Coated Steel Casing Borehole

Electromagnetic (EM) exploration is one of the most important geophysical methods for monitoring hydraulic fracturing. However, recently published research has focused on the effects of steel infrastructures while neglecting the contribution of the cement layer that interfaces between the casing and the surrounding geological formation. Additionally, they have ignored the effects of the anisotropic nature of subsurface structures, arising from both hydraulic fractures and natural fissures. In this article, we first analyze the transient EM (TEM) responses in various conductive backgrounds with cement-coated steel casing boreholes. We then investigate the effects of the anisotropic nature of subsurface structures caused by hydraulic fractures and natural fissures. To balance computational efficiency with accuracy, we model the hollow steel casing as a rectangular prism. Numerical results demonstrate that the presence of cement-coated steel casing not only alters the electrostatic field within the casing but also affects the distribution of geometric currents in the surrounding geological formation. Moreover, electrical anisotropy significantly influences the TEM responses. If processed with an isotropic model, potential artifacts could be introduced into the target images. These findings could enhance the accuracy of geophysical surveys in hydraulic fracturing operations, leading to more reliable detection and characterization of subsurface fractures and improving the management of extraction processes.