Modeling Anisotropic Crosswell Magnetic Responses: A Magnetic-Source Integral Approach with Air-Effect Analysis

Crosswell electromagnetic imaging serves as a pivotal method for analyzing the distribution of residual oil in oil and gas reservoirs, as well as for optimizing drilling strategies. Current challenges in crosswell electromagnetic (EM) modeling encompass large-scale discretization, with limited research addressing the effects of magnetic sources in anisotropic media or the influence of borehole air. This study introduces a novel iterative Fourier domain integral algorithm for three-dimensional (3D) magnetic-source magnetic simulation in an anisotropic medium. The proposed method employs the Fourier domain method and quasi-complete Fourier techniques to realize adaptive sampling and efficient 3D modeling. The accuracy and efficiency of the method are validated through models. Parametric analyses quantify the impact of several factors, including source depth, frequency, borehole air effects, and conductivity anisotropy on magnetic field components. For the dynamic monitoring of oil and gas reservoirs, the relationship among the magnetic field, frequency, and water saturation is discussed. Furthermore, comparative response differences between electric and magnetic sources are examined, thereby providing theoretical foundations for real-time EM imaging in anisotropic hydrocarbon reservoirs.