Research On Sequence Stratigraphy And Depositional System Of The Middle Third Member Of The Eocene Shahejie Formation In The Liangjialou Area,Dongying Sag

Liangjialou area is located on the slope in the southeast of Lijin sag,Dongying sag,Jiyang depression,Bohai Bay basin.It is one of the key exploration blocks of the oil production plant of the oilfield with"three facing depressions"in the structural position and significant source reservoir advantages.The area is rich in oil and gas resources and has a high degree of exploration,but previous studies mostly focus on oil and gas production.The research results of high-resolution sequence stratigraphy and sedimentary system of the middle member of the third member of Shahejie Formation(Es3~m)of Paleogene have poor comparability in the whole area.Guided by the standardized theory of sedimentology and sequence stratigraphy,through the comprehensive analysis of Geology and three-dimensional seismic data,this paper studies the fourth-order sequence stratigraphy and sedimentary system in Liangjialou area,and predicts the dominant development position of favorable reservoirs such as lithologic oil and gas reservoirs in the study area.According to the five common sequence stratigraphic boundaries in the study area,four third-order system tracts are identified in the third-order sequence(ESQ6):highstand systems tract(HST),falling stage systems tract(FSST),lowstand systems tract(LST)and transgressive systems tract(TST).Based on the stratigraphic relationship,shoreline trajectory and seismic reflection characteristics,13 fourth-order sequences(HRS1-HRS13)are further identified,and each fourth-order sequence is composed of T-R sedimentary cycles.Taking the fourth-order sequence stratigraphy as the research unit,the sedimentary system analysis of Liangjialou area is carried out,and several sedimentary facies such as Delta,lacustrine facies and gravity flow are identified.Among them,the delta plain mainly develops water distributary channel and flood plain microfacies,the delta front develops underwater distributary channel,mouth bar and sheet sand microfacies,and the deep-water gravity flow sand body is relatively developed.Therefore,the spatial distribution position of thin sandstone reservoir in this area is further determined.Based on the analysis of high-resolution sequence stratigraphy and sedimentary system,combined with seismic forward modeling and cooperative waveform cluster analysis,the reservoir properties of high-resolution sequence stratigraphy 1(HRS1)are classified,and the plane distribution positions of reservoir I,reservoir II and poor reservoir are obtained.The reservoir quality of fourth-order sequence HRS11-HRS13 is classified by carbon hydrocarbon detection technology.The prediction results are consistent with the comprehensive interpretation results of drilling,which is considered that this technology has strong applicability in the classification of favorable reservoir quality in the study area.In addition,the continental lacustrine basin is different from the marine basin.The former has the geological characteristics of"near provenance,multi provenance,rapid phase transformation and thin reservoir".Combined with the development characteristics of sedimentary system and on the basis of previous studies,this paper considers that the hierarchical control of structure,sediment supply and high-frequency dry-wet climate cycle are the main control factors affecting the stratigraphic development,and establishes a comprehensive control factor model of lacustrine basin sedimentary sequence represented by FSST.