Study On Diagenesis And Pore Evolution Of The 8th Member Reservoir Of The Sulige Area

Based on the local geological background of the Sulige Region in Ordos Basin,the Shihezi formation He 8 member of Permian in the upper Paleozoic stratum,we choose the Reservoir Geology and Sedimentology as a guidance,comprehensively using Cast Slices,SEM,CL,XRD,porosity test and homogenization temperature of Fluid inclusive to deeply study the petrologic feature and diagenesis in order to have a better research of porosity evolution of the district,find out the main reason of causing the tight reservoirs.The Sulige Region contains middle grain litharenite and lithic quartz or quartz sandstones,the well rounding and good sorting shows its high level of maturity in texture and composition.Secondary porosity mainly make up the reservoir spaces but the widely developed intergranular pore stills gives us a way of accumulating the Natural Gas which cannot be neglected.The fillings between the granule are mainly cement and less matrix which leads to the one cause of the loss of porosity.The diagensis is complicated and one reason of causing the tight reservoirs are compaction which squeeze the quartz,the cementation bring quartz?Kaolinite?chlorite and illite cement.The quartz are formed in concrescence edge,the rest are filling in the dissolved holes.Kaolinite takes the main composition of the clay minerals,chlorite is less and illite is the least.The dissolution have two methods,the major way of dissolve Rock debris and feldspar are acid-media fluid which causing massive secondary porosity,the other way of producing fewer pores is alkaline-media fluid which cause the corrosion of silicate minerals.Comprehensive analysis shows the period B of the middle diagenetic stage.Due to the severe heterogeneity of the stratum,we take the content of rock in 15%as a limit to separate the reservoirs into two groups which we called sublitharenite and litharenite with high content of plastic fragments.The sublitharenite reservoir takes the more quantity of secondary porosity and lesser fillings but the litharenite reservoirs are worse which cannot be the reasonable reservoirs in theory.The compaction is the primary reason of causing litharenite into tight reservoirs but the cementation is the dominate reason to bring the sublitharenite into tight.The dissolution gives a good recovery of the porosity in both kind of reservoirs.The result of calculation and lab test have a small error which proves the reasonability of the study...