Three-dimensional controlled-source electromagnetic forward modeling by edge-based finite element using secondary electric field

As an important complementary tool for seismic survey, the controlled-source electromagnetic (EM) method can be used to monitor reservoirs by detecting the subsurface electrical properties. In order to investigate theoretically feasibility of monitoring reservoirs by the controlled-source EM, a requisite component is to calculate the EM responses of three-dimensional conductivity model excited by the EM sources. Total fields varies rapidly and is difficult to simulate accurately for the region adjacent to the source locations, to this end, the primary field is calculated for a half-space or a layered-earth model as the source term. To bypass the problem that the divergence condition is unsatisfied when using traditional nodal element to model the electrical field, the partial deferential equation (PDE) for the controlled-source EM, based on the secondary electric field, is solved discretely by the edge-based finite element method. To model the responses at multiple frequencies, the frequency-adaptive mesh can be used to increase the speed of forward calculation while maintaining the accuracy. The algorithm is verified by comparing the analytic solution with the numerical solution for a three-layered conductivity model. The modeling results of a simple reservoir model demonstrate the possibility of the controlled-source electromagnetic method in reservoir monitoring. © 2015, Science Press. All right reserved.