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Study On Three-dimensional Forward Modeling For Transient Electromagnetic By Vectorial Finite Element Method

Posted on:2016-04-08Degree:MasterType:Thesis
Country:ChinaCandidate:W H YaoFull Text:PDF
GTID:2180330476451350Subject:Solid Earth Physics
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In recent years, Transient electromagnetic method gradually become a compelling geophysical prospecting method through the development and practice at home and abroad. However, due to the complexity of the transient electromagnetic theory, the current theory of technology is still not perfect, especially in the interpretation of three-dimensional forward and inverse process, which is far from practical level. The main reason is that the transient electromagnetic response characteristics and regularity of understanding is not clear in the three-dimensional space, And the current software can not accurately simulate complex earth-electricity model in three-dimensional space. With this situation, this article will focus primarily on the three-dimensional vector finite element transient electromagnetic fields forward, and hope to provide a scientific basis and reference for subsequent transient electromagnetic forward modeling and inversion study. Main content is as follows: First we derived the electric dipole field at any position in half homogeneous space. Then using the anomaly field method which is to load the background field produced by loop source in half homogeneous space into the equations of the anomalous electric field, We realized 3D loop source frequency domain forward modeling by the Witney type interpolation basis functions for solving discrete region, interpolation. The sparse matrix is stored by the CSR format and the equations are solved by the parallel solver PARDISO in the MKL library. We first calculated on a finite number of different frequency response with equal logarithm interval, and then inserted the response which need to be solved in the time domain transformation by the Cubic spline function, Finally achieved the time domain transformation by the cosine transform. We adopted Fortran language to write the program, and separately compared with the typical H-type, K-type digital filtering solution and found that the vector finite element calculation of transient electromagnetic response is more accurate by error analysis that the relative error of the vertical component is in five percent or less. Through compared with three-dimensional models response calculated by Wang & Hohmann’s three-dimensional FDTD algorithm, we further proved the correctness of vector finite element method. Based on the correct procedures, we calculated the central loop transient electromagnetic response half homogeneous space containing conductive body and containing resistive bodies, and analyzed the response excited by a large loop source in a half homogeneous space, half-space with a conductive bodies, and half-space with a resistive bodies, and found that vertical response on different planes is consistent with the smoke ring theory. Then we simulate the transient electromagnetic response of ground-air system of dip orebody excited by grounding electrical source, and calculated the global apparent resistivity section. The apparent resistivity section can more objectively reflect the size and occurrence location of underground anomalies.On this basis, we calculated the shallow sea tentative formula towed marine transient electromagnetic response of high resistance reservoir model in different water depth, different reception conditions, and analyzed the curve configuration and the response regularity. Finally we find that the depth of sea plays a vital role in the detecting of oil and gas reservoir. Based on the same scale and depth, the transient electromagnetic field, we observed, has large amplitude with small difference between the background and anomaly field in the shallower depth, while in the deeper depth, it has small amplitude with larger difference, in contrast. In the last article, some of the problems and future work is pointed out.
Keywords/Search Tags:Transient electromagnetic method, Vector/Edge finite element method, Three-dimensional forward modeling
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