3D FEM Numerical Simulation Of Borehole-ground Potential On Undulate Topography

Undulate topography has always been a difficult problem in geophysical exploration, especially for the complex areas. Field work are greatly influenced by terrain, hence, a prospecting method for oil, gas and mental reservoirs exploration is urgently needed on complex terrain conditions. The borehole-ground potential method is a exploration method which measures potential on the surface with the supply current source in the well. This method not only plays an important role in the exploration of the remaining oil distributions and the potential ore deposits in deeper and outer of the critical mines, also has been widely used in the aspects of hydrogeology, engineering geology etc. The theory of borehole-ground potential in level topography has been deeply developed by the domestic and foreign scholars study, so this paper is mainly focus on the3D finite element method numerical simulation of borehole-ground potential on the undulate topography.The total potential is divided into normal and abnormal potential in order to eliminate the singularity of source potential. Starting from the boundary value problem of borehole-ground potential, this paper derived the abnormal potential functional expression. The rolling terrain mesh is firstly divided into hexahedron units, and then the hexahedron units can be divided into five tetrahedron elements, wrote the corresponding program based on the finite element method process. In view of the large linear equations in the3D FEM, using the symmetrical super relaxation preconditioned conjugate gradient method to solve the equation, and that reduces the required memory of computer and improves the calculation efficiency and precision.Take examples with two typical surface of ridge and valley, the paper got the contrasts of abnormal potential contour map and the abnormal potential curve of a section on the undulate and level topography, and then studied the abnormal response of different target geologic body by the forward modeling of different geo-electric models, thus analyzed the effects on the borehole-ground method from the undulate topography.This article laid a solid foundation for further inversion imaging of undulate topographical borehole-ground potential, also had a guiding significance for the field production practice.