湖平面变化对浅水三角洲前缘砂体构型的控制OA

[Objective]In the middle and late stages of oil and gas field development,studying sand architecture is the key to accessing residual oil and enhancing recovery.Precise interpretation of similar outcrops provides a compa-rable prototype model for predicting underground reservoir architecture.[Methods]The shallow-water delta profiles of the Yan'an Formation in the Kaokaowusugou and Gulf Mining Industry in the Ordos Basin were the research objects.UAV oblique photography was used to obtain images of massive outcrops from which 3D digital outcrop models were established.Detailed interpretation of digital outcrop architecture was then carried out by combined field observation and indoor analysis.[Results]Developmental characteristics and evolutionary models of shallow-water delta front architecture during a time of rising lake levels were defined.When the lake level is low,mainly trunk-type distributary channels are developed,measuring 23.30-48.40 m wide×0.89-1.81 m thick,with an average width-to-thickness ratio of 26.74.The sandbody superposition patterns are mainly overlay type.As the lake level rises,fork-type distributary channels,mouth bars,sand sheets and subaqueous distributary bays gradually develop.The width of the mouth bar is 53.90 m,thickness is 2.21 m,width-to-thickness ratio is 24.39,and the sandbody superposition patterns is mainly lateral splicing type.When the lake level is higher,mainly terminal-type distributary channels,mouth bars and sheet sand architectural units are developed.Terminal-type underwater distributary channels,which are isolated in muddy deposits,have widths ranging from 4.70 to 25.30 m,thickness from 0.40 to 1.03 m,and the width-to-thickness ratio from 11.75 to 24.56.[Conclusions]When the source supply of material is relatively stable,an increase in lake level enlarges the accommodation space.The architectural units evolve from trunk-type to terminal-type distributary channels,depositing mouth bars and sand sheets.The size of the sandbody decreases,but its width-to-thickness ratio increases.Overall,the ratio between sandstone and stratum thickness decreases,spatial connectivity decreases,and reservoir heterogeneity is enhanced.