Three-Dimensional Modeling of Marine Controlled Source Electromagnetic Using a New High-Order Finite Element Method With an Absorption Boundary Condition

The marine controlled source electromagnetic method (MCSEM) is widely used in marine oil, gas exploration, and deep structures investigation because of its low cost and high efficiency. In this article, a high-precision forward algorithm for 3-D modeling for MCSEM is proposed. Unstructured meshes are used to discretize the model domain, and local mesh refinement techniques are applied, which is conducive to simulating complex terrains and targets. The application of electric dipole discrete technology can load wire excitation sources with arbitrarily complex spatial shapes, which can simulate more realistic electromagnetic field distribution of marine controllable sources electromagnetic in actual exploration. Absorption boundary conditions (ABCs) based on real number and exponential stretching techniques are introduced to improve the numerical solution accuracy. To improve the efficiency of solving, the open-source [multifrontal massively parallel solver (MUMPS)] based on the multifrontal algorithm is used to solve the finite element equations. Finally, some typical geoelectric models are designed to verify the correctness and effectiveness of the proposed algorithm. The calculation results show that higher order finite elements bring about higher accuracy. In addition, the loading of ABCs is simple and effective than conventional Dirichlet boundary conditions.

I. Introduction

The marine controlled source electromagnetic method is an effective tool for geophysical exploration, and it has been widely used in marine oil, gas exploration and deep structures investigation [1], [2], [3], [4], [5], [6]. With the great improvement of instruments and continuously advancing in data acquisition technology, exploration in complex marine geological environment is becoming more and more convenient, and large number of data have been collected. In order to make full use of these data and give out a reliable interpretation, we need some high accuracy and efficiency tools. High-precision inversion is one of them. As we know, forward is the basis of inversion, and the accuracy and efficiency of inversion highly depend on the forward algorithm. Thus, studying and developing a high-precision forward algorithm for inversion program is of great value in theory and application area.