Depositional Characteristics And Hydrocarbon Control Of West Slope Belt In Dongpu Depression

Central west slope belt in Dongpu depression is an important area for exploration.Using abundant drilling, logging, seismic and assay data, research has been carriedout dominantly for type III sequence framework and its correspond depositionalsystem together with high resolution sequence stratigraphy theory and method. TypeIV~V sequence framework and its correspond depositional system has also been studiedfor important sequences in important area, on the basis of which to investigatelithological reservoir distribution so as to resolve its formation model, toidentify exploration target of lithological trap and complete prediction evaluation.The study finally aims at exploiting the area for hydrocarbon exploration,discovering new reserves and reaching favorable exploration benefit.Using high resolution sequence stratigraphy theory and method 11 type IIIsequences have been classified, which are mainly composed of progradation andaggradation sequence set. Vertically it can further be divided into low level system,lacustrine flooding system and high level system.High frequency sequence was developed in interval S3 in west slope with frequentvibration of lake basin and alternating occurrence of high water and low water. Highlevel deposition exists in low level system as well as low in high system, whichalso caused frequent intercalation of sand and mudstone in S3 formation.Sedimentary facies study makes it more reasonable for understanding sedimentaryfacies types and depostional system in interval S3 in west slope in Dongpu depression.In the west mainly developed braid river delta and fan delta depostion.In west slope lithologic reservoirs consist of sandstone updipping pinchoutreservoir, lenticular reservoir sandstone (conglomerate) fan body reservoir andstructural-lithologic reservoir, among which small and deep structural-lithologicreservoirs are principle.Various sandbodies with high level braid river delta were developed on upthrowwall of Xingzhuang fault in west slope, while downthrow wall mainly developed lowlevel delta sandbody and high level turbidite sandbody. Upthrow wall mostlydeveloped various structural reservoirs and downthrow wall is the favorable areafor lithologic reservoir formation.