Research On Formation Mechanism Of Oil-gas Reservoirs Of S₂₊₃ Oil Layer In West Slope Region, North Songliao Basin

Based on predecessor's research results, formation condition of oil-gas reservoirs of S₂₊₃ oil layer in westslope region was comprehensively and systematicaly studied, through using comprehensively seismics,logging, well logging, core, analysis assay data and paleontology data and adopting the latest theories andtechniques and methods of structural geology, sequence stratigraphy, sedimentography, petroleum geology,and oil-gas accumulation dynamics, etc. Main controlled factors, periods and models of oil-gasaccumulation and distribution were identified, favorable exploration areas were forecasted, throughdissecting typical oil-gas reservoirs and analyzing oil-gas accumulation mechanism and process.Structural features of west slope region is simply by the study of structural and evolution characteritics inwest slope region, it is eastern slope unicline, structural plane map of each reflection interface express thatslope gradual decrease one by one from bottom to top. Structural evolution can be divided into three stagesof chiasmic, depressed and abortion equilibrium. Fault generally doesn't develop, main types are fault ofpost rift extend, fault of reverse-strike, fault of reverse-extension. Three-stage sequences and four-stagesequence framework, facies signs and sedimentation models were established by the study of sequencestratigraphy, the result shows that three-stage SQy_1-2 sequence develops delta and shore-mearesedimentation and delta is main, the transgressive system tract of distribution is finer. Three-stage sequenceSQy3 main develops transgressive system tract delta and shore-shallow lacustrine sandbars, shore-shallowlacustrine mixing beaches and eroded channel filling. During the early period of Yaojia formation, thelacustrine bank line waves in east edge of west slope region. Then source supply enough and detlta faciesespredominate. During the late period of Yaojia formation, the lacustrine bank line cosmically pusheswestwords and forms unique concomitant sedimentary pattem of delta-eroded channel filling-sandy beachbars sedimentary facies. Type of oil-gas reservoirs were dissected, the result shows that S₂₊₃ oil layer inwest slope region have four types oil-gas reservoirs, anticline, lithotogic updip pithing, structural-lithologic,fault barrier. Gas lies upper but oil lies bottom in the same layer, oil-gas distribute mainly in Taikang upliftzone and nearby in the plane, the types of oil-gas reservoirs are anticline and structural-lithologic inTaikang uplift zone. the types of oil-gas reservoirs are unconformity and lithologic updip piching in thewestearn overlap zone. Oil source are compared, the result shows that oil-gas of S₂₊₃ oil layer in west sloperegion come mainly from Qingshankou formation of Qijia-Gulong sag, oil-gas from Qijia-Gulong sagmigrated laterally westword through sandbody that connected by fault, there have three migration pathways,the first migration pathway is that oil-gas migrate from Qijia sag across Taikang to Fulaerji, the secondmigration pathway is from Gulong sag across Baiyinnuole to Erzhan and Alaxin, the third migrationpathway is Gulong sag across Bayanchagan to Tailai. Gas transporting ability of S2+3 oil layer in westslope region is evaluated, the result shows that most area of gas transporting ability is more higher butFulaerji, gas favorable migrate and accumulate to the west slope region. Based on the relationshiphydrocarbon distribution between formation condition of S₂₊₃ oil layer in the west slope region, the resultshows that hydrocarbon formation and distribution were mainly controlled by trap development,relationship trap between the room place of oil-gas migration pathway, convergence area of centrifugalflow and endocentric flow, etc. Oil-gas accumulation period is the end of Nenjiang formation sedimentation,Mingshui formation sedimentation and the early of Palaeocene. Migration and formation of hydrocarbonreservoir of S₂₊₃ oil layer in the west slope region have three models, migration and formation model ofsand uplift piching trap, migration and formation model of structural and stractural-lithologic trap.migration and formation model of fault barrier trap. Based on synthetical analysis of main controllingfactor of oil-gas accumulation and distribution of S₂₊₃ oil layer in west slope region, favorable area wassforecasted, the result shows that uplift zone of Taikang and nearby is favorable area of accumulation anddistribution of S₂₊₃ oil layer in west slope region, du405's sand uplift piching trap is favorable target area ofnext oil-gas exploration.