Abstract: At the mature development phase of an oilfield,the analysis of monogenetic sand reservoir architecture is efficient to instruct the research on the oil-water movement pattern and the operation of tapping remaining oil.Based on the reservoir configuration theory,this paper divided the composite sand reservoir into multiple monogenetic sandbodies in Oil-groupⅠ and Ⅱ of the E₃d₂^L in Oilfield Z of the Bohai Bay Basin using three vertical stage identification markers and four lateral delimitation identification markers.The vertical stage identification markers include shale interlayers,pebbly sandstones,calcareous interlayers and the lateral delimitation identification markers include logging curve shape difference,lithology difference,thickness difference and water flooding feature difference.Each monogenetic sandbody represents a single sedimentary microfacies (e.g.underwater distributary channel or mouth bars,etc).In addition,the definite logarithm correlation between interwell sandbody thickness variation and top boundary dip was used to quantitatively identify the pinch out point of the single sandbody.Therefrom,the subsurface complex sedimentary characteristics were reconstructed to display the contiguous distribution of mouth bars and the cross superimposition of underwater distributary channels within this oilfield.Combing with the other static and dynamic data,the comprehensive analysis revealed that the quality difference of monogenetic sandbody is the major factor influencing the oil-water movement and remaining oil distribution in the study area.The independent flow unit develops within the individual lobe,within which the different types of monogenetic sandbodies with different reservoir quality correspond to different seepage capacities and flooding features.The premium monogenetic sandbodies are prone to form dominant pathways and result in enrichment of remaining oil.The study of oil-water movement based on monogenetic sandbody analysis will provide a solid geological foundation for tapping the potential of remaining oil through infill drilling and enhancing the oil recovery in the oilfield.

Key words: monogenetic sand, delta front, water flooding pattern, reservoir quality difference, remaining oil, Dongyin Formation Bohai Bay Basin