Modelling the 3D TDEM response using the 3D full-domain finite-element method based on the hexahedral edge-element technique

In EM modelling, in order to accurately compute the responses of earth structures, it is necessary to take into account the inherent constraints in the components of the electric and magnetic fields. These include the discontinuity of the normal component and the continuity of the tangential component of the electric and magnetic fields at the boundaries. The use of the conventional node basis function finite-element method fails to produce accurate results, because in the approximation of the fields the method requires the continuity of all the field components at the inter-element boundaries of the finite-element cells. The edge basis function (vector) finite-element method is designed to overcome the problems, because it takes the whole vector of the field components in the approximation as one entity instead of independently for each field component. Compared to the conventional method, the method is also more efficient, because it is possible to solve for a single vector tangential component along the element edges instead of solving for three scalar field components at each element node. In this paper, an approach for modelling the transient EM response of geological structures based on the 3D hexahedral edge finite-element technique is presented. The approach is stable and accurate over a broad contrast range from low to very high conductivity contrasts (up to 100,000:1) and is capable of modelling complex 3D geological structures efficiently.