The3-D Numerical Simulation For Borehole-to-ground Resistivity Survey

Borehole-to-ground electrical method, is a exploration method, which set theexcitation source deep in the hole while putting survey grids on the ground to receivedata. For practical applications, the forward and inverse calculation of the theoreticalmodel is need. In this thesis, based on a previous study, a large number of forwardmodel tests are designed to verify the stability of forward calculation and analysis ofthe response characteristics of different models with existing programs, which hasimportant guiding significance for the practical application of the inversion and thepromotion of the theoretical model.The first question of the three-dimensional electrical borehole-to-groundnumerical forward modeling calculation is the forward equation calculation. We usefinite difference method, converting the differential equations to the differenceequations.We establish large-scale discrete difference equations, and finally use theincomplete cholesky conjugate gradient method (ICCG method) to solve it.Before the numerical model experiments, the authenticity of forward calculationhas been proved. We found that in the stage for calculating the forward areasubdivision by finite difference method, the boundaries expanded one is closer to thetrue value than the unextended one. In the numerical modeling stage, we designedbasic models to explore the law of the power supply, the orebody depth, and surfaceore body thickness parameters corresponding apparent resistivity. We found that theposition of point sources by changes in the depth direction of apparent resistivityanomalies and surface condition can be inferred center of the corresponding verticalextent of the underground ore body, and the surface of apparent resistivity response isalways the power attribute points around the orebody. We designed thin model bodylike veins, like a layered model topography and overburden fault model.For differentgeological features, we designed different targeted forward modeling, andsummarized the law between the particular model parameters and apparent resistivityon the ground. For different tilt angles ore vein, section through its surface apparent resistivity curve inflection point can determine the position of the edge of theunderground ore bodies. Overlay for the existence of ore, found low resistivityoverlay information for underground ore body shielding layer is covered withrelatively high resistance greater impact. For underground faults, through dramaticchanges in the amplitude of the surface as well as its apparent resistivity contour mapof the face, it is possible to infer the location of underground faults.