Study on Depositional Elements and Sandstone Body Development Characteristics Under High-Resolution Sequence Framework of the Fuyu Oil Layer in Bayanchagan Area

Summary With the development of oil and gas exploration, the tight oil in Daqing Oil Field has attracted attention. In recent years, the Fuyu oil layer in the northern Songliao Basin has become a focal point for exploration; however, the study of depositional elements in this area remains insufficient. Based on several analyses of sandstone thickness, depositional environment, heavy minerals, rock color, sedimentary structures, and logging curve characteristics, as well as stratigraphic division and comparison in the Bayanchagan area’s Fuyu oil layer, it has been revealed that the clastic source directions are northwest and west. The area features river-dominated, shallow water lacustrine delta deposits. These deposits are further divided into two subenvironments: delta plain and delta front, encompassing eight depositional elements. The main depositional elements are distributary channels, crevasse splays, floodplains and overbank sand lenses, subaqueous distributary channels, river mouthbars, interdistributary bays, and frontal splays. The whole oil layer in the study area is in the background of a transgressive deposition, during which lake level oscillates and several water regressions occur, thus establishing the sedimentary evolution characteristics of the oil layer in the study area. The Fuyu I (FI) sandstone thickness and oil layer thickness in the study area are the largest, with the widest distribution range, while the Fuyu III (FIII) is the least developed; the Distributary channels are the most effective oil and gas depositional elements. Vertically, the FI and Fuyu II (FII) oil layers are the most developed, and gradually deteriorate downwards.