Sedimentary Model Of Slumping Gravity Flow And Its Significance For Hydrocarbon Exploration

With the development of oil & gas exploration,the deep-water turbidite reservoirs are becoming one of important goals for oil-gas exploration and development in the Bohai Bay basin,east China.Deep-water turbidites can be subdivided into flooding turbidite and slope-slumping turbidite according to their triggering mechanism.In this thesis,sequence stratigraphy,sedimentology,reservoir geology,petroleum accumulation of the slope-slumping turbidite system fed by Dongying delta were studied based on a large number of core,well logs and seismic data of the third middle sub-member,Shahejie formation in Dongxin area,Dongying depression.Some progresses are proposed in sedimentary characteristics,sedimentary process,reservoir evaluation and hydrocarbon accumulation.Firstly,sequence stratigraphic framework was rebuilt during this study.Moreover,a short lived,large-scale hiatus between the third middle sub-member and the third lower sub-member of Shahejie formation was regonized.The third middle sub-member was divided into one third-order sequence,three system tracts and ten parasequence sets.The tenth,ninth and eighth sand groups belong to lowstand system tract(LST),and the seventh sand group belongs to transgressive system tract(TST),and the sixth to the first sand group are belong to highstand system tract(HST).Secondly,four gravity flow deposits,i.e.slide,slump,debris flow and turbidity current are identified according to core data from 38 wells.Debris flow can be subdivided into sandy debris flow,muddy debris flow and mud flow.Statistics showed that turbidite system was dominated by sandy debris flow and sandy slump while turbidity current played a little role in deep-water deposition in study area.Thirdly,a new sedimentary model characterized by non-channelization sedimentary architecutures was summarized and the traditional lacustrine floor fan model was modified.Channel-style and nonchannel-style sedimentary models for gravity flow were proposed on basis of identification of six sedimentary architecture units of gravity flow including channel,channelized lobes,tongue-like debrite,thin-bed turbidite sandstone,slide and slump.Fourthly,relationships between sandstone genesis,reservoir scale,physical properties and oil bearing possibility of turbidite system were systematically analyzed in this thesis,which suggested that slide and sandy debrites were the best reservoirs with high porosity,permeability and oil bearing.Then,lacustrine deep-water reservoir was evaluated sand group by sand group.As a result,channelized lobes and tongue-like debrite dominated by debris flow are thought as the best exploration targets.Finally,two hydrocarbon accumulation models,i.e.source-controlled model and fault-controlled model,are summarized in this thesis.Prediction of sandstones and faults providing migration route of hydrocarbon are the key controls for hydrocarbon exploration in the east part of study area.However,distribution of overpressure area of source rocks and prediction of sandstones with high porosity are the key controls for hydrocarbon exploration in the west of study area.