Study On 3D Forward Modeling Of Complex Resistivity Method Of Finite-length Wire Source

As we all know, rocks and minerals have complex resistivity properties because of the induced polarization effect, and now the study of controlled-source electromagnetic forward modeling and inversion mostly considers electromagnetic effect, ignores the IP effect, and assumes that underground resistivity does not change with frequency. This paper is from the fact, carried out the three dimensional forward modeling research of complex resistivity method for long wire sources that has taken into account the IP effect and electromagnetic effect. The method involved physical parameters more effectively less geophysical inversion of multiple solutions explained, can more accurately determine the division of geological anomaly and provide more information for accurate geological interpretation.Firstly from Maxwell’s equations, the derived point dipole by schelkunoff potential recursive solution, then its integral along the wire will be the analytical solutions of the long wire source, can be seen from the expression in the long wire source analytical solutions related to the two grounding item.Through the comparative analysis of electromagnettic fields generated by point dipole and a long wire source,found that the longer the power pole pitch, the greater the difference of electromagnetic field between both and thought in a certain extent, can use multiple point dipole instead of a long wire source. In the three-dimensional forward modeling,the method is diretly to solve total field, not to get electromagnetic field by dividing into background field and abnormal field, uses the equivalent source of current density distribution is pseudo delta function instead of electric dipole, so as to avoid the source singularity, and improves the compu-tationnal efficiency. To simulate the long wire source field, in order to join the continuous long wire source in the binned grid, setting multiple point dipiles on the grid nodes to replace long wire source that is equivalent to superpose multiple point dipole to achieve the goal of simulating longwire source field. After compared with analy-tical solutions of long wire source,found that the relative error between the electromagnetic field components and carney apparent resisitivity and phase of 3D forward modeling and the analytical solution is smaller, verifying the multiple point dipoles instead of long wire source of feasibility.Finally, using a wide range of Cole-Cole complex resistivity model are introduced into 1D and 3D forward modeling, and completed the preparation of the program. Through change Cole-Cole model parameter to analysis its parameter on electromagnetic field distribution of effect, in 1D forward modeling, found that electric field changes more largely than magnetic field, and apparent resistivity and phase curves are well reflected; in 3D forward modeling, find the distribution of electromagnetic field is more influenced by zero-frequency resistivity and polarizability than time constant and frequency correlation coefficient.