Sedimentary microfacies of the Cretaceous shallow-water lacustrine delta deposits in the Songliao Basin:An example from the Pu I 1-3 oil reservoirs of the eastern Xing-3 block, Xingshugang Oil Field, Daqing

On the basis of well logs, mud logs, analytical data and regional geological background, the present paper conducts a systematic study of the types, characteristics, association patterns, planar distribution and evolution of the sedimentary microfacies in the Pu I 1-3 oil reservoirs of the eastern Xing-3 block, Xingshugang Oil Field, Songliao Basin. The shallow-water lacustrine delta deposits in the Pu I 1-3 oil reservoirs consist of two sedimentary subfacies including the delta distributary plain and delta front subfacies;11 sedimentary microfacies including the distributary channel, abandoned channel, natural levee, crevasse splay, overbank thin-bedded sheet sandstone, interdistributary bay, subaqueous distributary channel, subaqueous crevasse splay, distributary channel mouth bar, sheet sandstone and subaqueous interdistributary bay microfacies, and 7 sedimentary microfacies associations including the distributary channel-overbank thin-bedded sheet sandstone, distributary channel-natural levee-overbank thin-bedded sheet sandstone, distributary channel-natural levee-crevasse splay-overbank thin-bedded sheet sandstone, distributary channel-abandoned channel-overbank thin-bedded sheet sandstone, distributary channel-interdistributary bay, subaqueous distributary channel-distributary channel mouth bar-sheet sandstone-subaqueous interdistributary bay and subaqueous distributary channel-sheet sandstone microfacies associations. On the whole, the Pu I 1-3 oil reservoirs have undergone several evolutionary stages of early regression, middle stable deposition and later transgression, during which the lake basin displayed the wide-narrow-wide scales, and gradual decrease of the thickness and ideal drilling rates of the skeletal sandstones.