Research On Shale Gas Forming Conditions Of Chang 7 Member Of Yanchang Formation In Wuqi-Zhidan Area,Ordos Basin

Ordos Basin has abundant oil and gas resources,chang 7 member of Yanchang formation developed in the heyday of the lake basin.Wuqi-Zhidan area,as the study area,is in the center of the lake basin in the chang 7 sedimentary period.In order to clarify the main controlling factors of shale gas accumulation,this paper have done analysis testing of source rocks,reservoir physical properties and other aspects on the basis of the collection of a large number of geological,logging,analysis data and on-site core observation,including Flake identification,organic geochemical testing,pore osmosis analysis,x diffraction analysis,field emission scanning electron microscopy,gas analysis.This paper makes an in-depth study on the formation conditions of shale gas in the chang 7 member of Wuqi-Zhidan area,and obtains the following new understanding.The results show that the study area is mainly composed of deep lake facies,the thickness of the shale is 90m,large and continuous.TOC content is high,between 2.01%and 12.03%.This paper establish the TOC log interpretation model of Wuqi-Zhidan area with multipleregression analysis method,and fitting effect is better,which can be used to evaluate the plane change of abundance of organic matter in the study area.Organic matter type is mainly II,and maturity is high.Ro is between 0.7%-1.2%.Pyrolysis peak temperature is mainly distributed between 440-460?.It is concluded that Wuqi-Zhidan area has the material guarantee of shale gas generation,and the thermal evolution reaches the stage of generation of oil and gas.The composition of mud shale minerals in the study area is mainly quartz and clay minerals.The average content of quartz is about 31.11%.The clay minerals are mainly composed of chlorite,illite and Yimeng mixed layer,and the content is about 28.98%.The brittleness index is distributed between 0.53 and 0.75.The average porosity is 2.82%and the permeability is 0.028x10-3?m2.The Analysis of field emission scanning electron microscopy show that the pore type of the shale in the study area is mainly composed of intergranular pores,and the development of organic matter is poor.The pore size is mainly distributed between 30-300nm,mainly mesopore-macroholes and little micropores.Shale throat radius distribution is between10.79nm-190nm,mainly between 15nm-30nm,which is the nano-pore throat.Shale reservoir pore permeability conditions are poor.We can learn that the gas distribution range is between 2.6m3/t-5.5m3/t from the gas measurement data,which is greater than the shale gas development standards lower limit.It is found that the gas content of shale is affected by shale thickness,the content of TOC,quartz,clay minerals and other factors.Based on the gas potential?measured shale gas content and reservoir characteristics,the evaluation criteria of the study area are established,and the favorable evaluation area of shale gas is predicted.