The Research On 3-D Fast Forward And Inversion Of Surface-borehole And Borehole-surface IP Methods

As one of effective in-hole geophysical methods, In-hole IP(Induced Polarization) method is widely used in deep prospecting of hidden polymetallic and noble metallic deposits. Overseas, In-hole IP method has become a routine measure even for every borehole. In the current domestic mineral exploration, In-hole IP is gradually becoming one of the important deep mineral exploration methods. Because of the borehole conditions and environmental constraints, surface-borehole azimuthal IP survey and borehole-surface Mise-a-la-masse IP method is widely used. At present, however, there are a few researches and explain level is relatively backward, resulting in direct impact on deep exploration results. Therefore, Ministry of Land and Resources national crisis mine succeeding resource prospecting office listed "three-dimensional forward and inversion research of surface-borehole and borehole-surface IP methods" as one of the deep mineral exploration key techniques. In line with the state to mine development and the demand for deep exploration, this paper carries out 3-D fast forward and inversion research on surface-borehole and borehole-surface IP methods.The boundary value and variational equation of point-source electrical field of three-dimensional geoelectric section were presented beginning with the differential coefficient of potential. Then, interweaving tetrahedron grids, which provide flexibility and veracity for borehole and undulate terrain, are applied to 3-D FEM forward modeling. As the result, the computation is more efficient and calculation accuracy is improved. Based on detailed analysis of the non-zero elements of 3-D forward coefficient matrix, MSR (Modified Sparse Row) compression and storage technology is used and memory requirements of forward calculation have been greatly reduced. SSOR-PCG is applied to solve the equation so that forward calculation time is significantly reduced. In the general PC, forward calculation is achieved in tens of seconds, which lay the foundation for rapid inversion explained.The third chapter analyzes anomalous characteristics of surface-borehole azimuthal IP survey of different forms of abnormal blind orebody beside borehole. Besides, the impacts of anomalous body position, directions from the borehole, the borehole size, environment and topography are discussed. In the end, it sums up the rapid positioning blind orebody method according to anomalous characteristics of different directions observation. Based on non-equipotential anomalous body, anomalous rules of Mise-a-la-masse IP of cube and tabular body are discussed in the fourth chapter, and the impacts varying of anomalous body depth and charging point's position are also analyzed. All of these provide a reference to the actual work.In the fifth chapter, owing to insufficient observation datum of surface-borehole 5-direction IP survey, 3-D tomography inversion is not feasible. So, man-machine mutual interpretation software is developed on "approximate analytical solution" forward, and the interpretation of the measured data shows a satisfactory result. Moreover, this paper deduces the 3-D tomography inverse algorithm based on the least squares constrained theory. The conjugate gradient (CG) method and approximate calculation of Ax and A~Ty are used to inversion of surface-borehole IP and borehole-surface IP to avoid the calculation and storage of Jacobian matrix and speed up the inversion.This paper realizes the 3-D fast forward and inversion programs of surface-borehole and borehole-surface IP, and develops the man-machine mutual forward fit interpretation software used to surface-borehole 5-direction IP. 3-D forward is about tens of seconds, and 3-D tomography inverse is only about 10 minutes. These programs and softwares are of good application prospects.