Tight Sandstone Gas Reservoir Formation Process

Based on drilling core,field outcrop observation and logging,well logging data,through experimental methods,such as core observation and conventional thin section identification,grain size analysis,scanning electron microscopy(SEM),research the sedimentary facies,petrological characteristics,physical property and diagenesis characteristics of the eastern basin of Shanxi formation,Mainly through the characteristics of fluid inclusions and the uniform temperature,it determined the periods and time of hydrocarbon filling,combining regional burial history and regional sedimentary structure diagram,put forward the corresponding relations of diagenetic stage division and the pore evolution,establishes gas reservoiring pattern of upper palaeozoic in Ordos Basin,combining the tectonic evolutionary-thermal history,hydrocarbon generation-deposition/diagenetic history of the basin,analyzed the development process of densification and tight gas reservoir formation.Reservoir of Shanxi formation in the study area is typical low permeability tight reservoirs,mainly for the quartz sandstone and lithic sandstone.Area of Shanxi formation sandstone suffers strong compaction and cementation,but weak denudation,with secondary porosity is given priority to,it has the characteristics of low permeability reservoir,low oil saturation,low pressure and other significant characteristics.Research indicates that there are mainly two phase of gas(oil)filling,the first phase of filling time is between 190Ma-170Ma,it was from early Jurassic to middle Jurassi,the quartz sandstone reservoir has been started developing from the low permeability reservoir to the densification reservoir,The second phase of filling is between 160Ma?115Ma,is was late Jurassic to early Cretaceous,the reservoir has already been to the densification reservoir during this period,that's to say the formation process is filling while densifying,due to the second phase of the gas filling is the main original gas reservoir accumulation period,in general,the formation process of tight gas in the study area is densifying while forming.