New insights into reservoir architecture of Fuyu oil layer in southern Songliao Basin based on analyses of water-flooding characteristics

Fuyu oil layer of Fuyu oilfield located in southern Songliao Basin, NE China, has been in high water-cut stage after more than 50 years' water injection. According to the cores of the inspection wells, the distribution of the remaining oil is inconsistent with predictions. The water-flooding characteristics playing an important role in controlling remaining oil distribution were studied by the cores, the logging data in dense well spacing area, as well as the measurements of porosity, permeability, and remaining oil saturation. Based on the water-flooding characteristics, the reservoir architecture and sedimentary environment of Fuyu oil layer were discussed. The results show that Fuyu oil layer is not characterized by the water-flooding law of a typical distributary channel in delta systems, that the lower single sand body always has a higher water-flooding degree than the upper as it consists of channels with single sand body scale (1-2 m) and stably distributed interchannel mudstone with a thickness of 10-30 cm. The specific reservoir architecture also indicates that the sedimentation of Fuyu oil layer has undergone frequent alternations of rivers and lakes. The results not only point out the distribution of remaining oil for such mature oilfields but also offer a new method to recognize the reservoir architecture.