Influence of diagenesis on reservoir in He 8 member of the Permian Shihezi Formation in Longdong Area, Ordos Basin

Abstract:As a typical representative of unconventional gas reservoirs, tight sandstone gas reservoirs have the characteristics of large reserves and rich oil and gas resources, and have become an important exploration and development target for the government and enterprises. As one of the large oil-bearing basins in China, Ordos Basin contains many sets of oil-bearing strata, which are rich in oil and gas resources and have obvious characteristics of source-reservoir-cap assemblage. Longdong area in the southwest of the basin, under the influence of sedimentary environment and tectonic factors, continuously deposited a set of relatively complete tight thick sandstone, and the multi-layer system is generally rich in oil and gas. With the deepening of the exploration of tight sandstone oil and gas, the area has gradually become a new oil and gas development replacement area.The physical properties, lithology, pore structure and other parameters of the reservoir in the study area were studied by using casting thin section, scanning electron microscope, high pressure mercury injection, physical property analysis and gas testing data. The results show that the main rock types of He 8 member in the study area are lithic quartz sandstone ( 61.6 % ) and lithic sandstone ( 15.06 % ). The grain size of the reservoir is coarse and the sorting is medium. The pore types are mainly intragranular dissolved pores, followed by intergranular pores and intercrystalline micropores.The reservoir thickness range and lithology in the study area vary greatly and the heterogeneity is strong. Reservoir properties are controlled by sedimentary facies and diagenesis. Sedimentary facies fundamentally control the reservoir physical conditions, sand body structure has an important influence on reservoir physical properties, cutting type single sand body reservoir physical properties is relatively good, splicing type sand body reservoir physical properties, poor isolated single sand body.Compaction is the main reason for the densification of reservoir physical properties. Water mica is the primary factor for the densification of reservoir caused by cementation. The dissolution degree of reservoir is low, and the effect of improving reservoir quality is limited. The research results can provide reliable geological basis and scientific basis for further exploration and development of the lower section of He 8 in Longdong area.