The Study Of Reservoir Characteristics And Control Factors Of Chang7 Tight Sandstone Reservoir In The Jiyuan Area Of Ordos Basin

According to the core observation,casting thin-section,cathodoluminescence,SEM,grain size analysis,conventional mercury injection,rate-controlled mercury penetration,NMR,this thesis researched the distribution characteristics of sedimentary facies and sand body,reservoir petrology and microscopic pore structure,diagenesis and diagenetic evolution,resistances and dynamics of oil migration during oil filling and accumulation timing,path of oil migration.On the basis of above,to comprehensively analyze the main controlling factors of reservoir accumulation in research area and built oil accumulation model,guided by the theory of petroleum geological accumulation.Main knowledge obtained as follows:Deltaic and lacustrine facies were developed during the period of Chang7 reservoir in Jiyuan area.During chang7₃ deposit period,the lacustrine basin was deepest,and mainly distributed lacustrine facies,the high quality source rocks with thick layer are developed in formation,and the turbidite sand bodies are developed in the center of the lacustrine basin.Duiring chang7₂ and chang7₁ deposit period,the lacustrine basin shranked,deltaic deposit facies was the major sedimentary facies,high quality reservoir developed in underwater distributary channel.Sandstone of chang7 in research area mainly consist of lithic arkose sandstone with good sorting.The content of the cementation is high,which mainly consist of iron calcite,kaolinite and illite.The pore type is mainly the feldspar dissolution pore,and the remaining inter-granular pore is the second.As the layer deepened,the content of quartz decreased,the content of cementation and debris increased,and the plane porosity decreased.The reservoir pore throat is narrow,which dominated by the nano-scale pore throat system,the average poreradius is 18.82?m,and the average throat radius is 0.85?m.The type of diagenesis is rich and complex,mainly by mechanical compaction,cementation and dissolution.Because the chang7 foramtion is deeply buried,and the content of rigid debris particles is low,the mechanical compaction is developed,and greatly reduces the primary pores.The cementation produces a large number of fillings,blocking pores and further reducing the physical properties of the reservoir.The dissolution increases the pore throat of the reservoir and is beneficial to the physical property of the reservoir.The diagenetic facies of chang7 resevoir are illite cementation facies,carbonate cementation facies,feldspar dissolution pore facies,residual inter-granular pore phase and inter-granular pore-feldspar dissolution facies.Feldspar dissolution pore facies,residual inter-granular pore phase and inter-granular pore-feldspar dissolution facies are favorable areas for reservoir development.The tight sandstone is accumulating location for tight reservoir,also the main path of oil migration.Therefore,the quality of reservoirs is an important factor determining the degree of reservoir enrichment.Based on the macroscopic and microcosmic factors,the classification and evaluation criteria of the reservoir were formulated,and the reservoir was classified and evaluated.From chang7₁ to chang7₃,the quality of the reservoir gradually deteriorated.Due to the influence of sedimentary facies and diagenesis,the high quality reservoirs of chang7₁and chang7₂ was developed,and the quality of chang7₃ reservoirs was poor.chang7₁ and chang7₂ are the main mining formation in the research area.The resistances of chang7 hydrocarbon migration is capillary force causing by tight pore throat,the average is 2.04MPa.The dynamics of hydrocarbon migration is residual pressure in the process of hydrocarbon generation by source rocks,the average is 14.8MPa.The path of migration is consist of structural fracture,fracture pore,lithologic bedding and reservoir pores.Chang7 tight reservoir is mainly controlled by source rock distribution,high quality sedimentary facies and reservoir,source-reservoir combination.Source rocks provide direct oil source and dynamics of hydrocarbon migration for reservoir,sedimentary facies and reservoir quality influence the migration and diffusion of oil in the reservoir,the source-reservoir combination controls oil filling speed and final saturation.