Research On Burial-diagenetic Evolution Process And Densification-hydrocarbons Filling Temporal Sequence Of The He 8 Tight Sandstone Reservoir In The Eastern Ordos Basin

He 8 sandstone reservoir of Permian Shihezi formation of the upper Paleozoic in the eastern Ordos basin has good gas exploration prospect.Domestic research on diagenetic-porosity evolution process,burial-thermal history,hydrocarbon filling history of tight sandstone reservoirs basically stays at an independent,single static research phase at present.Study on the sequence between densification process and hydrocarbon filling attributed to the petrological components of of sandstones and their differential diagenetic evolution process is still weak.The detailed micro study on sandstone types,petrological components and their diagenesis,diagenetic-hydrocarbon filling-porosity evolution was made,dynamic evolution history of burial-diagenetic-hydrocarbon filling-pore evolution of the He 8 Group of the Upper Paleozoic in the eastern Ordos Basin was constracted,based on the microscopic research and quantitative statistics of all kinds of slices under microscope,analysis of scanning electron microscope,fluorescence of thin sections,observation under fluorescence of liquid inclusions,measurement of cathodoluminescence and homogenization temperature and chemical composition of liquid inclusions,combined by study on the burial-thermal and hydrocarbon-injection history of the study area.On the basis of preceding research,porous reduction and raise of different sandstone types caused by diagenesis was quantitatively calculated,and the differences of diagenetic-pore evolution,the sequence between densification process and hydrocarbon filling was discussed in the paper.The research results show that the primitive characteristics of sandstone type,framework mineral composition and textural maturity of He 8 sandstone reservoir in study area decide the original physical properties of sandstone and affect its diagenetic evolution process and diagenetic product.Because of different diagenetic evolution process,the physical properties of various types of He 8 sandstone reservoir are different.Basing on early basal carbonate cementation,calcium cementation sandstone basically lost most of the pore and become tight reservoir,after experiencing the stage A of middle diagenetic phase.The pore loss rates caused by cementation and compaction average separately were 25.0%and 5.2%,and residual pore average was 3.8%.The pore increasing rate caused by dissolution was limited(average0.3%).After experiencing intense compaction of early diagenetic phase,high plastic lithic sandstone lost most of the pore and become low porous and permeable reservoir,and some even become tight reservoir.The pore loss rates caused by compaction average was up to 22.4%,and high plastic lithic sandstone reservoir basically can not provide effective space for late fluid flow after deep burialism.The pore loss rate caused by cementation was low(average5.2%),and residual pore average was 5.4%.The pore increasing rate caused by dissolution was limited(average0.7%).Gas bearing the quartz sandstone and lithic quartz sandstone experienced two periods of dissolution,three periods of hydrocarbon filling and more complicated diagenetic process,and formed various pore assembly types.They are favorable gas-bearing sandstone types of He 8 sandstone reservoir in study area.The main diagenesis of the two types of sandstone which caused pore loss was compaction and cementation.The pore loss rates caused by compaction average separately were 14.5%and 13.2%,and the pore loss rates caused by cementation average separately were 11.8%and 10.6%,and residual pores average separately were 8.6%and 9.4%.The pore increasing rate caused by dissolution was limited,but it is higher relative to the other two types of sandstone(average 1.4%and 0.9%).He 8 sandstone reservoir experienced three periods' significant hydrocarbons filling.The time of the first phase of hydrocarbons filling was last phase of T3 to J1(210Ma?175Ma),and it formed before secondary overgrowth of quartz.It shows dark blue-blue fluorescence and low-medium maturity,and its filling scale is limited.The time of the second phase of hydrocarbons filling was J2 to K1(165Ma?100a),and it happen before the late carbonate cementation but after illite cementation.It filled particles crack,crack and other native aperture,all kinds of solution pores and fractures,and widely distributed.It shows light blue fluorescence and high maturity,and its filling scale is large,which is the mainly hydrocarbons filling stage in study area.The time of the third phase of hydrocarbons filling was K2(90Ma?70Ma),and it happen after the late carbonate cementation.It mainly along the cracks and dissolution system into the reservoir,and it distributed in hydrocarbons filling ? distribution zone and replaced,dissolved and partially covered the hydrocarbons filling ?.It shows bright blue fluorescence and high maturity,and its filling scale is slightly smaller then the hydrocarbons filling ?.This research provide important informations for insighting into all kinds of physical chemistry,fluid and diagenesis environment,and formation mechanism of reservoir performance evolution,through the study on different diagenetic-hydrocarbon filling-pore evolution process combined by microscopic research and macroscopic geological background.