Characteristics And Controlling Factors Of Intermediate-Deep Clastic Reservoirs In Shahejie Formation In Baxian Sag

The hydrocarbon exploration has entered into middle-high mature stage in Baxian Sag,nonstructural traps of intermediate-deep are important areas of incremental reserves in the future,systemical research of intermediate-deep clastic reservoirs has an important guiding significance for hydrocarbon exploration.Based on the geological and geophysical datum,sequence stratigraphy,sedimentary petrology and reservoir geology as the instructional theory,through thin sections,cathodoluminescence,scanning electron microscopy and X-ray diffraction experiment etc.,a systemical research of sedimentary facies and diagenetic characteristics,discussing the reservoirs characteristics and main control factors of intermediate-deep clastic reservoirs.The Sha-3 Member of Shahejie Formation comprises 3 third-order sequences,deposits on braided fluvial delta,fan delta,nearshore subaqueous fan and lacustrine.The intermediate-deep sandstones are and rock types are mainly lithic arkose and arkose.The sandstones have a low degree of compositional maturity and a moderate degree of textural maturity.The intermediate-deep clastic rocks undergo compaction,cementation,dissolution and metasomatism etc.,and being A1 substage at present.Four types of diagenetic facies are recognized on the basis of the diagenetic minerals and diagenetic characteristics.They are tightly compacted,carbonate cemented,clay mineral filling,and unstable components dissolved.The sonic,resistivity,and gamma ray logs,which are sensitive to diagenetic facies,were selected to establish the logging criteria for diagenetic facies.As a constructive diagenetic facies,unstable components dissolved facies has a low to medium GR,medium AC and highly variable RT values.The reservoirs are low to extra-low porosity and extra-low to ultra-low permeability.Reservoir spaces consist of primary pore,secondary pore and mixed pore.Between 3600~3700 m and 4000~4100 m,the reservoirs develop two anomalously high porosity zones.The deposition mainly controls sedimentary facies,sand body thickness,sorting and rock fabric,etc..Compaction and cementation are the main actor reducing reservoir quality,the reduction of porosity of the former is greater than the latter.The dissolution is mainly responsible for improving reservoir quality,furthermore,early hydrocarbon charging and overpressure are beneficial to protect the primary pore.