| This peper on the background of Longmen Mountain geological and geophysical structure, premise on magnetotelluric sounding, by study the electrical structure of magnetotelluric sounding profile which across the Longmen Mountain thrust belt and Western Sichuan foreland basin, combination with seismic and geological structure data to study the deep electrical structures of Longmen Mountain thrust nappe, the geometry of main detachment surface, the ancient uplift and depression that may be exist in Western Sichuan foreland basins, basement structure of Western Sichuan Depression and so on,to provide geological and geophysical basis for background research of oil and gas.The Paper Collection Anxian- Suining magnetotelluric data which is section of Songpan - lichuan - Shaoyang geology and geophysics profile,re-process and interpretation. Focus on analysis of curve type to understand the basic electrical layer of this region; analysis of sectional drawings of resistivity and phase to recognizing the overall electrical structure, structure contours,fracture distribution and so on; analysis of the polarization characteristics to understand the structural trend and two-dimensional nature; analysis of total vertical conductance to understand the ups and downs status of the basement; use one-dimensional Bostik transform to determine the depth of the inversion ,provide initial model for the two-dimensional inversion,and use other information supporting constraints to do two-dimensional Occam inversion, inversion mode contains TE, TM and TE + TM inversion, finally,chose the results of joint inversion to interpretation. According to the results of Occam two-dimensional inversion and the magnetotelluric reflection coefficient imaging results to study the Anxian - Suining electrical structure of the upper crust. Based on electrical structure, combined with surface geological observations, divided Anxian-Suining magnetotelluric profile into three electrical structure belt for its electrical structure is different obviously: Longmen Mountain eastern margin electrical structure belt, western Sichuan foreland depression electrical structure belt, central Sichuan electrical structure belt.Study on the characteristics of the three electrical structure belt detailedly. According to the electrical structural characteristics suggested the existence of ancient uplift and depression for the first time.According to Luqu-Longmen Mountain-Zhongjiang magnetotelluric profile, Malcolm-Dujiangyan-Pixian magnetotelluric profile,Anxian - Suining magnetotelluric sounding profile and WFSD-1 AMT profile,the peper analyze of deep electrical structure of thrust nappe structure and geometry of Yingxiu fault which is Longmen Mountain thrust beltthrust nappe structure main detachment surface.Using Luqu-Longmen Mountain-Zhongjiang magnetotelluric profile,Anxian - Suining magnetotelluric profiles and Yingxiu - Jianyang long period magnetotelluric profile, compilation of the basement depth chart of the middle of Western Sichuan foreland basin for the first time,to study structure and buried depth of basement of the basement,for the basement structure controlled the geological evolution of sedimentary cover, and then controlled the deposition of Western Sichuan foreland basin marine strata, to find local uplift structure in the basement is benefit of further search for enabling accumulation environment of oil and gas.According to the ancient uplift of Magnetotelluric profile and basement to study the background of hydrocarbon occurrence, the ancient uplift and basement fractures controlled the geological evolution of western Sichuan depression, the ancient uplift controlled migration and accumulation of oil and gas, within the ancient uplift control, low-amplitude structures of large syncline has reservoir conditions. According to magnetotelluric, seismic, gravity and magnetic, geological and petroleum, etc., analyze of oil and gas occurrence background of the Western Sichuan foreland belt, preferably some hydrocarbon favorable block. |
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