Deep Clastic Reservoir Characteristics And Diagenetic Evolution In Dehui Fault Depression Of Songliao Basin

The deep clastic reservoirs have large burial depth,strong diagenesis and heterogeneity,high densification,complex reservoir evolution,and high exploration risk in Dehui fault depression of Songliao Basin.In this thesis,rock and mineral test and analysis methods such as common thin slices,cast thin slices,scanning electron microscopy,and X—ray diffraction are used to study petrological characteristics,physical properties,pore structure,diagenesis,diagenetic facies and diagenetic evolution of deep reservoirs,and establish pore evolution model.The results are obtained as follows:The lithology of deep reservoirs is dominated by feldspathic lithic sandstones and lithic feldspar sandstones.The compositional maturity is low,the roundness is sub-edges,the separation is moderate—good,and intergranular is line contact.Pore type is dominated by secondary pores,the pore structure is generally poor,with Yingcheng Formation being relatively good,deteriorating with depth,and develop two types of reservoirs: ultra-low porosity—extremely low permeability,and ultra-low porosity/low porosity—extremely low permeability.The reservoirs diagenesis of Dehui fault depression in Songliao Basin are from A—substage of middle diagenesis to the B—substage of the middle diagenesis.They underwent destructive diagenesis,such as mechanical compaction and cementation,and constructive diagenesis such as dissolution.The diagenetic facies are divided into 4 types,the D phase is the most important constructive diagenetic facies.Evolutionary sequences are basically the same,strong compaction—early calcite cementation—quartz secondary—acidic water-dissolution—late cementation.Through quantitative calculation,the pore evolution model of the Upper Jurassic and the Shahezi Formation and Yingcheng Formation in the Lower Cretaceous were established.The difference in initial porosity is not significant.The pore evolution process of the Lower Cretaceous is similar to that of the Upper Jurassic.It underwent early compaction and reduction of pores,early cementation and pore reduction,acidic dissolution and increase of pores,re-buried cementation and pore reduction,and the current porosity are calculated to be 5.50%,4.18% and 7.22%.The calculated results matches well with measured porosity.