Quantitative Simulation Of Physical Properties And Pore Evolution Of Tight Sandstone Reservoirs

The authors selected the Shanxi formation in the eastern Ordos Basin,and analyzed the characteristics of rock minerals by means of thin slice observation,cathodoluminescence,electron microscope scanning,and fluid inclusion temperature measurement.With the help of basin simulation software and quartz precipitation kinetics model,the authors analyzed the pore evolution process of sandstone from various stages of diagenesis.The Shanxi formation in the target area is a series of coal bearing strata,with sand-shale interbed.Among them,quartz sandstone in the lower part of the Shan2 section is generally gas bearing in the target area.But the porosity of the reservoir is at the average of?4.19⁵.3?%.The average permeability of its permeability is?0.208⁴.52?x 10^-3um².It is a special low porosity and ultra low permeability reservoir.The Hg curve of the quartz sandstone reservoir of the Shan2 section has a small slope.The curve has a wide curvilinear platform.This phenomenon indicates that the quartz sandstone reservoir has the largest pore throat and the pore structure is more homogeneous.Diagenesis research reveals that quartz secondary growth is very developed,mainly in the I and II stage,and occasionally in the III stage.Fluid inclusions are widely developed in the secondary enlargement of quartz.The homogenization temperature of inclusions in I stage secondary quartz enlargement is usually at?80¹20??.The homogenization temperature in secondary enlargement quartz of II stage is usually at?130¹60??.Combined with inclusions data of the quartz overgrowth edge,quartz precipitation and basin dynamics model diagenetic burial history data analysis,The initial porosity of the Shanxi formation is about 50%when it enters the diagenetic process.In the A stage of early diagenesis,from the beginning of sedimentation to 220 Ma ago,the formation depth is about1362 m.In this stage,compaction plays a major role.The simulation results show that the porosity decreases by 11.90%when the depth reaches 1362.0m.The total porosity at this time is 38.10%.When entering the B stage of early diagenesis,220Ma-206Ma,the stratum depth is1362.0m-1906.5m.According to the simulation results,the geothermal temperature is 65⁸5C,and the cementation of quartz begins.The porosity is down by 3.22%.At this time the total porosity is only 34.88%.When entering the A stage of late diagenesis,206Ma-138Ma,the stratum depth is 1906.5m-3010.0m.At this time,the secondary growth of quartz in the II stage of sandstone develops.Siliceous cementation results in a 17.06%decrease in porosity.At this time the total porosity is only 17.28%.When entering the B stage of late diagenesis,138Ma-93Ma,The ground temperature is greater than 140?,and the buried depth is more than 3010.0m.Siliceous cementation results in a 11.91%decrease in porosity.The total porosity is only 5.37%.Sandstone densification further intensified development,it is the result of the combined effects of tight sandstone diagenetic environment and diagenesis.