Comparison Of The Geological Conditions Of Shale Gas In The Middle And Lower Yangtze Region

This Paper is inspired by the exploration success of Eyiye well 1,using field investigation,sample testing,and experimental analysis to compare the sedimentation-tectonic evolution background,the organic geochemical characteristics of shale,shale reservoirs,and isothermal adsorption characteristics of shale formation in the middle and lower Yangtze,this paper probe into the forming conditions and resource potential of middle and lower Yangtze shale gas.(1)The whole area of middle Yangtze region is rich in dark mudstone formation,the Shijintuo group is a set of dark-colored mud shale and silty sand deposited under anoxic environment.It is widely distributed.But the lower Cambrian hetang formation in the lower Yangtze region is characterized by carbon-silica-bearing shale,grayish-black thin-layer silica-bearing rocks,with a thickness greater than that in the middle Yangtze area.(2)The type of kerogen in middle Yangtze region is Ⅱ.The total organic carbon content is between 0.15% and 9.64% with an average of 2.33%.The type of kerogen in lower Yangtze isⅠ.The total organic carbon content is between 0.13%-38.39% with an average of 4.78%.The organic matter type and organic matter abundance in the lower Yangtze region are superior are superior to those in the middle Yangtze region.(3)The shale vitrinite reflectance Ro in the middle Yangtze region is between 2.0% and 5.0%,which is generally over mature;the vitrinite reflectance Ro in the lower Yangtze region is greater than 3.0%,and the highest energy reaches 4.94%,it is in mature and overmature stage.The thermal evolution degree of shale in the middle and lower Yangtze areas is similar,which belongs to the stage of superheat evolution.(4)The average content of carbonate minerals in the Shuijintuo formation in the middle Yangtze Region is about 58.5%,which is three times that of the Hetang Formation in the Lower Yangtze Region,and the average content of clay minerals is 28.1%,Which is about 15.9% lower than that of the Hetang Formation in the Lower Yangtze Region.Other minerals,such as plagioclase,K-field,pyrite,etc are not much different.(5)The pore size of the secondary dissolution hole in the Shuijintuo Formation shale in the middle Yangtze region is between 1and 10μm,the microfractures are between 1-2μm,shale porosity is between 0.41% and 21.42%.The shale pore size of the Hetang Formation in the lower Yangtze region ranges from 2 to 20μm,microfractures are between 1 and 2.5μm,and the average porosity of shale is 2.06%.Because the percentage of carbonate minerals in the middle Yangtze region is much higher than that in the lower Yangtze region the permeability of shale pores in the middle Yangtze region is better than that in the lower Yangtze region.(6)The intensity of tectonic transformation in the middle Yangtze region is weaker than in the lower Yangtze region.