Abstract: Aiming at the troubles of rapid phase change and difficulty in prediction of sandbody in Fuyu tight oil reservoir of Sanzhao Sag, the sedimentary characteristics and evolution of shallow water delta in Sanzhao Sag were analyzed in combination with core, seismic, logging and other data, as well as based on the division of high-resolution sequence framework. The results showed that the Fuyu oil layer is divided into 2 long-term semi-cycles and 4 medium-term cycles, and the datum plane dropped to the lowest at MSC3; the study area was dominated by delta plain distributary channel, delta front underwater distributary channel and sheet sand deposit, with meandering stream and shore-shallow lacustrine deposit in some places. In the context of water advance following water recession in the Fuyu reservoir, the datum plane evolution experienced four stages, including slow decline in early stage, rapid decline in middle stage, slow rise and rapid rise in late stage, with obvious differences in sedimentary facies types and sandbody distribution characteristics in different evolutionary stages. This study can provide a geological basis for the reservoir sandbody prediction of Sanzhao Sag.

Key words: tight oil, shallow water delta, sedimentary characteristics, sedimentary evolution, Fuyu oil reservoir, Sanzhao Sag, Songliao Basin