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ABSTRACT
We analyze the sensitivity of a three-dimensional crosswell electromagnetic (EM) system based on finite-difference time-domain modeling. To reinforce the simulation accuracy of low-frequency electromagnetic propagation in a small space, we limit the boundary reflection energy by suppressing the numerical dispersion of convolutional perfectly matched layers. The numerical simulation results for an isotropic medium indicate that an anomalous conductivity will induce a large magnetic field strength disturbance at the receiving coils in the X- and Z-directions, and a relatively large absolute sensitivity is observed at the receiving coils in the Y-direction. The three-component signals are most sensitive to high-resistance anomalies. Through an experiment that involved moving an anomalous conductivity disturbance, comparison plots of dynamic residual hydrocarbon monitoring between wells and depth determinations of anomalous conductivities are provided. The optimal acquisition depth interval of the receiving coil in the homogeneous medium is given, and the effective exploration area and optimal modeling region of the crosswell EM system are obtained.
Acknowledgments
Sinan Fang is supported in part by the China Postdoctoral Science Foundation (No. 2017 M622382) and Key Laboratory of Exploration Technologies for Oil and Gas Resources, Ministry of Education, Yangtze University (K2018-16). Zhi Wang is supported by the National Natural Science Foundation of China (No. 41604093)