Abstract: In order to clarify the controls of barriers/interlayers on the distribution of remaining oil in the braided-river reservoirs, taking the sand set II in the third member of the Guantao formation (N₁g₃^Ⅱ) in the Liuguanzhuang area of Dagang oilfield as an example, and using the data of core, testing, logging, and production performance, the criteria for quantitative identification of barriers/interlayers were established for the target interval in the study area, and the hierarchy, genesis of barriers/interlayers and their controls on remaining oil distribution were determined. In the study area, the barriers/interlayers in the target interval can be divided into 3 categories such as barriers between sand sets, interlayers between sand bodies, and interlayers within a sand body, which are developed near the architecture boundaries of the 7th-, 8th-, and 9th-order sand bodies, respectively. The barriers between sand sets are dominated by floodplain mudstones and silty mudstone, with thickness ranging from tens of centimeters to several meters. They can efficiently seal oil and gas vertically and allow the edge water to advance preferentially along the formation during development, leading to severe water flooding, and thus the remaining oil is mostly distributed in the upper parts of the complex mid-channel bars and braided channels far from injectors. The interlayers between sand bodies are mainly composed of fine-grained sediments in abandoned channels and gullies, with thickness typically ranging from 0 to 2 meters. They locally hinder vertical fluid migration and laterally control the distribution of remaining oil in different sand bodies, leading to two remaining oil distribution patterns: one is controlled by abandoned channel and the other by gully. The interlayers within a sand body are primarily associated with lateral accreted and interchannel mud deposits, and fall-silt seam, with the thickness reaching tens of centimeters, leading to three remaining oil distribution patterns, which are controlled by laterally-accreted mudstone, fall-silt seam, and interchannel mudstone, respectively.

Key words: Dagang oilfield, Liuguanzhuang area, Guantao formation, barrier and interlayer, floodplain, fall-silt seam, abandoned channel, remaining oil distribution