Application Of Magneto Telluric Sounding In Shale Gas Exploration In Xuefeng Mountain Area

The middle devonian-lower carboniferous deposits in Lianyuan sag of xiangzhong are more than 5,000 meters thick,which is the target area for oil and gas exploration after sichuan basin and the representative area of Marine sedimentation in south China.The purpose of the work is carried out in Lianyuan sag and northwestern Xuefeng mountain in devonian system and Cambrian system as the main goal of MT prospecting,clarify the research structure and the distribution of fracture system characteristics,main stratigraphic unit,buried depth,and the main properties of gas-bearing shale index,based on investigation and well shale gas exploration results,to determine the distribution,thickness of each series of strata,lithology changes,evaluation of shale gas geological conditions.MT section spans the northwest of Jishou-Lianyuan depression and is divided into three sections: Jishou-Xuefeng mountain,Xuefeng mountain-Anhua,Anhua-Lianyuan.Shatianqiao formation of the upper devonian,qiziqiao formation of the middle series,tiamajan formation,niutitang formation of the Cambrian,and bopaang formation of the devonian have relatively good tight oil and gas storage conditions,its organic rich shale is 1.3%-3.7%,and the Ro value is generally greater than 3%.The biogenic combination,dominated by Marine bacteria and algae,has favorable organic geochemical conditions for shale gas accumulation.The field source of magneto telluric sounding method is plane electromagnetic wave with vertical incidence,which simplifies the study of field greatly.At the same time,it has the advantages of large exploration depth,low exploration cost and convenient construction,can penetrate high resistivity layers,has strong ability to distinguish the target layer of relatively low resistivity hydrocarbon source rocks in the area,high horizontal discrimination,and mature data processing and interpretation technology,which can provide an important basis for the evaluation of oil and gas exploration prospect areas and become an important exploration means.The geological and geographical environment of Xuefeng mountain area is complex.In order to obtain objective and reliable measured data,this paper firstly carried out a large number of experiments and optimization on the selection of field parameters.The data collected contains interference information of various causes,which affects the data quality.The data processing method of magneto telluric sounding is discussed in detail to remove interference and extract useful abnormal information,so that the processed data is both smooth and accurate enough to provide a better data model for subsequent inversion.Of second,in order to avoid the explanation,guarantee the stability of the interpretation according to the existing regional geological and geophysical data,according to the results of the Bostick inversion profile semi-quantitative explanation,to roughly understand target horizon electrical characteristics,when the 2-d inversion Bostick inversion results as the initial input model,and combined with the existing geological and geophysical data of constraints;Finally,through the comparative analysis of MT section 2-d inversion interpretation results,seismic and borehole data in Jishou-Lianyuan area,the paper delineates the structural distribution and the advantageous area of shale gas reservoir in the study area,providing a technical basis for finding shale gas resources in Xuefeng mountain area in western hunan.