The Hydrocarbon Accumulation Mechanism Of Typical Depression Troughs In Erlian Basin

The petroleum resource is abundant in sub-sags of the Erlian Basin,but research about the hydrocarbon accumulation mechanism is relatively weak.Through type classification with twenty-three sub-sags,this dissertation selects four sub-sags to make petroleum geochemistry research,and finally build different types of accumulation models and different main controlling factors of petroleum accumulation.The sedimentary filling types of twenty-three sags could be divided into three types and fifteen subtypes,such as high source rock maturity large brackish sag.The structural types of twenty-three sags could be divided into five types,such as single fault groove sub-sag.The hydrocarbon generating potential could be divided into three levels which are rich,normal and non-hydrocarbon generation sags.High mature sub-sags and mature brackish sub-sags are of rich hydrocarbon generation condition.Furthermore,the condition that sub-sag area is bigger than 100 square kilometer is necessary for the formation of rich-hydrocarbon generation sub-sags.Based on differences of biomarker indexes,hydrocarbon source rock formation models of four typical sags could be divided into salty water algae source conservation model,freshwater or brackish water mixed supply model and freshwater higher plant supply model.Different models of source rock are of different geochemical characteristics,different hydrocarbon generation and expulsion thresholds,as well as different oil window width.The genetic types of crude oil generated by different source rock could be divided into three categories and nine sub categories.Different subcategories crude oil is distributed as zone or layer.Crude oil in the menggulin and xiaoabei reservoir of the anan sub-sag is mainly migrated through unconformity-fault-unconformity which is a stepped way migration.Crude oil in the wulanhua south sub-sag is mainly migrated vertically through fault.Crude oil in the aershan layer of the wuliyasitai south sub-sag is mainly migrated laterally through the T8 unconformity,whereas crude oil in the lower part of the first member of tenggeer formation is migrated laterally along sand body.Crude oil in the bayindulan south sub-sag is mainly migrated laterally along sand body.In the four typical sub-sags,the aershan fault zone,the inner zone of the South Wuya slope and the Ba I structural zone have the characteristics of high-strength filling,while the other zones are mostly of medium or low-strength filling.The crude oil of four sub-sags is mainly charged in the Teng-2 and the Saihan period,but crude oil of salty sub-sags is charged earlier,and crude oil of structure near the deep sag zone is charged more often.At present,the basin is mainly a hydrostatic low-pressure system,but the oil column height is less than the critical oil column height driven by buoyancy,hence,buoyancy and paleo abnormal pressure are the driving forces of oil and gas filling in the deep depression during the geological history.The petroleum accumulation model of different structural type sags could be divided into four types.Water salinity during the source rock deposition period controls source rock formation model.Hydrocarbon source stove controls the source,distribution and exploration potential of crude oil.Sag structural types control the migration and accumulation of crude oil.