Diagenesis And Pore Evolution Of Chang 6 Reservoir In Jiyuan Area

The Ordos Basin is an important oil-bearing sedimentary basin on the land of China,and the Triassic Yanchang Formation is its main oil-bearing horizon.This paper mainly studies the diagenesis and pore evolution of the low-permeability reservoir of the Chang 6 oil-bearing formation of the Yanchang Formation in the Jiyuan area of the Ordos Basin.The reservoir performance and hydrocarbon-bearing properties of reservoirs are extremely important factors restricting the development of oil and gas resources in the study area.Therefore,This paper mainly studies the reservoirs of the main low-permeability clastic rocks in the Chang 6oil-bearing formation of the Yanchang Formation in the Jiyuan area of the Ordos Basin.Workers are of great significance to the exploration and deployment of oil and gas in the region and the selection of favorable exploration targets and the improvement of oil and gas reservoir theory in the study area.In order to reveal the diagenesis of the clastic rocks in the Jiyuan area and its quantitative influence on the pore evolution,the favorable reservoirs are searched,and under the premise of comprehensively summarizing the work of the predecessors,the scanning electron microscopy?SEM?and the castings are used based on the core observation.Thin-film identification,X-ray diffraction analysis?XRD?of clay minerals,mercury intrusion testing,etc.have been comprehensively applied to the petrological characteristics,physical properties,microscopic pore structure,and diagenesis of reservoirs in the study area.The study suggests that the pore evolution and diagenetic evolution in the study area are coupled.The formation mechanism of secondary pores includes dominant sedimentary facies,dissolution and abnormal high pressure.The diagenetic evolution stage is mainly from the A to B stages of the diagenetic rocks.The reservoir space appears in the composite form of various types of pores.The residual intergranular pores and feldspar dissolved pores are the main ones.The intergranular dissolved pores,the lithic dissolved pores and the intercrystalline micropores are in the secondary position in the pore formation.The change in permeability is mainly related to the degree of development of the pores,the size of the pore throat,and the degree of connectivity between the pore throats.The results show that the diagenesis of the six groups of clastic reservoirs in the Ordos Basin includes compaction and pressure dissolution,cementation and dissolution;compaction,calcite cementation and quartz enlargement are the main factors for the decrease of reservoir physical properties in this area.The reason is that the dissolution is the constructive diagenesis of the formation of secondary pores;affected by the alkaline fluid generated by the early karst cream layer and the organic acid discharged from the source rocks in the middle and late stages,the reservoir of the gypsum interval has experienced alkaline and acidic.The diagenetic environment is controlled by the diagenetic environment.The clastic reservoir is mainly composed of cementation and pore reduction in the early diagenetic stage,and dissolution and pore enhancement occurs in the middle diagenetic stage.Based on a large number of analytical data of different depths and different horizons,preliminary formation has been formed.Quantitative characterization of pore evolution.Physical properties show that the porosity of this area is mainly between9.81%-11.25%,and the permeability is mainly in the 0.31-0.86×10^-3?m2 sandstone reservoir.The heterogeneity is strong,which is low porosity and low permeability reservoir.Compared with other areas in the Ordos Basin,the reservoirs in this area are denser and have poor reservoir performance.The high-quality sandstone reservoirs are mainly controlled by the diagenesis and diagenesis facies,source and source rocks.The type of rock that is most conducive to pore formation and preservation is quartz sandstone,followed by lithic quartz sandstone.Reservoir fractures play an important role in the seepage of oil and gas.In particular,high-angle fractures provide a channel for oil and gas migration to form oil and gas reservoirs.The pore evolution in diagenesis has positive significance for the development of the Lower Permian Yanchang 6 Formation low permeability reservoir in the Ordos Basin.