Identification of Reservoir Water-Flooding Degrees via Core Sizes Based on a Drip Experiment of the Zhenwu Area in Gaoyou Sag, China

Abstract

In order to identify the degree of water flooding in a reservoir and to discover any remaining oil-enriched areas, in this paper, a systematic study on the water flooding of cores in obturated coring wells is carried out. With observations and testing data of the cores, based on the notion of sedimentary facies, the water-flooding degrees of 4–7 sand groups in member one of the Paleogene Sanduo Formation (E2s14–7) of the Zhenwu area in the Gaoyou Sag are determined. Overall, the results show that the study area is formed under the background of lake regression, with various sedimentary systems, mainly including delta facies, braided fluvial facies, and meandering fluvial facies. The degree of water flooding is determined using a point-by-point drip experiment of the core. Combined with the testing results of the core, the water-flooding degrees of the different sedimentary facies are quantitatively determined. Identification standards for the water-flooding degree of delta facies, braided river facies, and meandering river facies are established. The water-flooding degree of the delta sand body is generally weak, with an oil saturation rate of 24.1–40.2%, essentially indicating no water flooding or weak water flooding. The water-flooding degree of the braided fluvial sand body significantly changes, and the variation range of the oil and water saturation measurement results is also large. The water-flooding degree of the meandering fluvial sand body is weaker than that of the braided fluvial sand body, which is mostly not flooded or weakly flooded. The water-flooding degree is obviously controlled by the sedimentary rhythm and the sedimentary type. The top of the positive rhythm, the bottom of the sludge bed in the braided fluvial point bar, the deltaic front subaqueous distributary channel, and the point bar in the meandering fluvial have relatively low water-flooding degrees. They are the subjects of subsequent development adjustment and the remaining oil potential tapping.