The Research And Application Of Thin Layer Geological Resolution In The Magnetotelluric

The resolution of the magnetotelluric sounding method is a very complex and important problem, and as a resolution problem of magnetotelluric method of thin layer geological detection, has always been one of the important content of the magnetotelluric sounding research. The study of thin layer resolution geological body, can give a lot of important concept, clearing and recognizing the geological body resolving power and its response characteristics of thin layer in the different occurrence condition, to the field construction design and indoor data processing and interpretation have an important guiding significance. Therefore, the thin layer of geologic body in one-dimensional and two-dimensional medium resolution forward modeling study is very necessary.This article summarized and based on a series of achievements of the experts and scholars, and has carried on the system research to the thin layer geological resolution of magnetotelluric sounding. First of all, this paper derived apparent resistivity formula of homogeneous medium and heterogeneous medium in the magnetotelluric sounding method, and clearly presented the object of study in this paper—thin layer geological body, based on magnetotelluric sounding clear concept and its distinguish standard in one-dimensional and two-dimensional medium model. In one-dimensional medium, basing on the typical three-tier geoelectric model, when the middle layer as a thin layer is studied in detail, its change of physical parameters of the buried depth, thickness and resistivity and so on, go to the effect rule with thin layer distinguish ability, and analyzes the two kinds of equivalent phenomenon existing in the thin layer, and the parameters changes affect to the thin layer distinguish ability in multilayer medium, finally summarized thin layer distinguish condition of geological body in the one-dimensional medium. Rsearch shows that: in the uniform horizontal layered media, the factors that influence the thin layer geological resolution in magnetotelluric sounding, mainly depends on the thin layer thickness, buried depth and wall rock resistivity ratio, and magnetotelluric sounding can distinguish for thin layer of its rock resistivity ratio and thickness of the buried depth ratio was positively related to relationship; With 5% relatively uniform error of distinguish standard in one-dimensional layered media, when:2 1SS ?0.4, and 2 0? ? ?0.15,2 1h h ?0.035, the low resistance thin layer can be distinguished, when:2 1h h ?0.286, and high resistivity thin layer and the resistivity of surrounding rock exists obvious difference, high resistance thin layer can be distinguished. Second, in the two-dimensional medium model, analyzed the factors of different polarization mode, different inversion method, different distance of measuring points, and topographic relief on the effect of thin bed resolution, compared the thin layer geological differentiating of horizontal, vertical resolution and border picking up in TE and TM polarization mode, and generalize some occurrence conditions in twodimensional medium, the relationship between transverse size and longitudinal depth size. Research shows that: for the longitudinal resolution of thin layer, TE polarization mode should be given prioritized, for the delimited of transverse size of thin layer, the TM polarization mode should be given prioritized; Without considering the other factors such as instruments, noise, device, when the resistivity ratio of low resistance thin layer and the surrounding rock is 0.05, thin layer depth surpass the transverse size of 160%, low resistivity thin layer becomes indiscernibility, when the resistivity of high resistivity thin layer and surrounding rock exists obvious difference, the maximum resolution depth of high resistance thin layer is 40% of the transverse size, but its resolution is mainly because of the influence of buried depth and thickness, under the condition of indiscernibility, changing transverse size will not improve the resolution of the high resistance of thin layer.Finally, based on the "upper middle yangzi focus area of Marine oil and gas geologic integrated research, and the evaluation of the district" project, " deep gold mine secondary exploration" project as an example, and taked the theoretical research results of geological resolution to apply in the actual data. When the actual drilling data and geological data shows that there are geologic abnormal body, and electrical inversion profile has not been a response in accordance with the actual data of abnormal traps, combined with the work area geological data, drilling data and physical property statistics, comprehensively analysed the relationship between the comprehensive reflection of response profile, which is reflected on some factors of thin layer geological body, such as buried depth, thickness, the resistivity differences of surrounding rock, its size, and the thin layer geological limit of resolution in magnetotelluric sounding, and then for the response and unresponse of the geological body of electrical inversion results section in thin layer to provide scientific analysis.