关键词: 分块线性变化, 线源, 频率域可控源电磁法, 有限元正演模拟

Abstract:

In order to simulate continuous conductivity of subsurface medium and inverse continuous medium, we worked on the finite element forward modeling on line source of FCSEM (frequency domain controlled-source electromagnetic) for two-dimensional block linear change of conductivity. In each unit, the linear interpolation both for electrical field and conductivity parameter was used, which would keep conductivity changing continuously between each unit. Firstly, boundary value problem and variational problem were given for finite element simulation. And the meshing, interpolation, unit analysis and total synthesis of FEM (finite element method) were discussed in detail. Secondly, sparse storage and BICGSTAB algorithm based on incomplete LU decomposition were used to solve complex equations, which had saved memory and improved compute speed. Then, a homogenous half space model was simulated and its result showed that the FEM numerical solutions of low and high frequency agreed with analytic solutions very well, which proved the correctness of this algorithm. Finally, a horizontal layered model and a vertical fault model were calculated, the contour maps both for apparent resistivity and phase reflected anomaly quite well. All of these had showed this algorithm can simulate the line source of FCSEM for continuous conductivity effectively.

Key words: block linear change, line source, frequency domain controlled-source electromagnetic, finite element forward modeling