2.5-D numerical simulation of the marine controlled-source electromagnetic method based on isoparametric FEM for the conductivity orthotropic medium

We have made a 2.5-D numerical simulation of the marine controlled-source electromagnetic method based on isoparametric finite element method for the conductivity orthotropic medium. The electromagnetic field coupling equations of wave number are derived by Fourier transformation, and the corresponding finite element equation is deduced by adopting the Galerkin weighted residual approach. The surveyed region is subdivided by arbitrary quadrilateral elements, and the biquadratic interpolation is conducted in the element turning the finite element equation into linear algebraic equations; finally, the linear equations are solved and the spatial domain electromagnetic field value is obtained through inverse Fourier transformation. This method can simulate the complex model of any shape of the conductivity orthotropic medium under submarine rugged topography. By comparison with the analytical result of the conductivity anisotropy of horizontal layered earth, the validity of the method is verified. The numerical solutions also match well with the results of marine controlled-source electromagnetic adaptive unstructured finite element method in two-dimensional anisotropic conductivity model in existing literature, which further verifies program correctness. The horizontal submarine 2D geoelectric model inspects the influence of various anisotropy coefficients on marine controlled-source electromagnetic response. The value of submarine rugged topography geoelectric model indicates that the resistivity anisotropy will bring obvious influence on marine controlled-source electromagnetic response, and it may mask the abnormal phenomenon caused by submarine topography and highly resistive oil and gas reservoirs.