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Research Of 2D CSAMT Tensor Data Inversion

Posted on:2016-08-19Degree:MasterType:Thesis
Country:ChinaCandidate:B GuiFull Text:PDF
GTID:2180330461492727Subject:Geological Engineering
Abstract/Summary:PDF Full Text Request
The most important feature of the CSAMT method is the use of an artificial source, which greatly increases the electromagnetic signal strength and makes up for some shortcomings, such as the weak signal of natural field source, difficult to observe and so on. The CSAMT method has been widely applied to oil and gas exploration, mineral prospecting, hydrology environment investigation, etc., and played a huge role. In addition, it has a high efficiency, small high resistance shielding effect, the horizontal and vertical high resolution and other advantages.However, the traditional CSAMT method mostly uses single dipole device of scalar measurements, which is suitable for simple geological environment rather than complex geological exploration. The second deficiency is the observation limit of single dipole transmitter. The position of source is needed to be adjusted in long section observation and area observation. If then source is disposed on faults, the source effect will cause the difficulty in processing those data. So the research of tensor CSAMT data inversion has practical value and is very necessary.In forward, two mutually perpendicular sources which oblique 45 ° to the survey line are divided into parallel X-axis and parallel Y-axis sub-field source, then we separately calculate the electromagnetic field components produced under the role of sub-field source and calculate the tensor impedance elements through tensor impedance formula. Finally, we compute the apparent resistivity and phase by Cagniard resistivity formula. We calculate the electromagnetic field components generated by individual electric dipole using the secondary field method to reduce the impact on the results of the source and improve accuracy. The forward matrix equation is formed by the finite element derivation, solving the equation to get the results in wavenumber domain, and finally we get the spatial domain results by reverse Fourier transform.In the inversion, the focus is the calculation of sensitivity matrix. In this paper, we use adjoint equation method proposed by Mc Gillivray et al to calculate the sensitivity matrix, and the sensitivity matrix of the different electromagnetic field components can be obtained by selecting a different source. In the calculation of the sensitivity matrix of apparent resistivity and phase, the method proposed by Rodi in 2001 is used. The data-space inversion based on the improvement of Occam inversion is employed to inverse the synthetic data, and good results have been obtained by inverting different models, which verifies the correctness and reliability of the algorithm. The trial inversion with real data shows that the inversion algorithm can be used for processing and interpretation of the measured data.
Keywords/Search Tags:CSAMT, tensor, adjoint equation method, data-space
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