The Characteristics Of Reservoirs And Caprocks, And Their Effects On Gas Accumulation In He8 Member From Sudong Block Of The Sulige Gas Field

On the basis of previous studies,guided by the theory of sedimentary petrology,reservoir geology and hydrocarbon accumulation geology,this paper makes a comprehensive study on the characteristics of the He8 reservoirs and caprocks in Sudong block of Sulige gas field in Ordos Basin by using geological data,such as logging data,gas production testing and so on,as well as analysis test data such as casting thin sections,particle size analysis,SEM,etc.,This paper analyzes the main controlling factors of reservoir physical properties and the reservoir controlling factors of the gas reservoir.Studies have shown that:Combined with core observation,according to the grain size,lithology,color and sedimentary structure of sediments,it is determined that the sedimentary facies of He8 member in Sudong block of Sulige gas field is fluvial facies,He8~2 is braided river facies,and He8~1 is meandering river facies.The lithic sandstone and lithic quartz sandstone are the main rock types in the study area,and the content of lithic quartz sandstone in He8~2 member is higher than He8~1member.The grain size of sandstone is mainly medium sand-coarse sand,the sorting of sandstone clastic particles is moderate,and the grinding roundness is mainly sub-angular.The chlorite,kaolinite and illite are the mainly interstitial materials.The main pore types are dissolved pores and intergranular pores,dissolved pores are the important components of the present pore space.The diagenesis study shows that the original porosity of sandstone is 37.4%,the porosity lost during compaction is 21.7%,the residual porosity is 14.5%after compaction,the loss of cementation process is 14%,the remaining porosity is 1.2%after cementation.The porosity is increased by 1.3%in intergranular pores and 6.3%in dissolution process.Lithology is different,the porosity loss of lithic sandstone during compaction is 22.4%,that of cementation process is13.8%,and the porosity of dissolution process is 4.9%.The porosity loss of lithic quartz sandstone during compaction is 19.5%,and the loss of cementation process is 15.3%.The porosity increased 10.0%for dissolution.He8 reservoir is invided into four categories in study area.Among them,the high quality reservoir of type?and type?are distributed in the region of high-energy mid-channel bar with relatively good physical properties,lithic quartz sandstone enrichment,lithic dissolved pores are relatively developed and coarse grain size.The reservoir of type?and type?accounted for 67%of He8~2-2,and in He8~2-1 is 56%;He8~1 reservoir is low quality,mainly are type?and type?.The upper Shihezi formation is the regional cap in study area,and the mudstone from He5 to He8 is the direct capstone of He8.Under the premise of sufficient gas source conditions,the distribution of gas reservoirs is controlled by multi-factors,such as reservoir physical property,sand body thickness,caprock,pore type ect..The physical property of reservoir and the thickness of sand body control the distribution of gas reservoir in the region,,the natural gas is enriched in the area with relatively good physical property and large sand thickness.The lithic quartz sandstone and lithic dissolved pore affect the physical property of reservoir at the microscopic level,and they control the enrichment of natural gas,the cap rock indirectly controls the distribution of gas reservoir macroscopicly.