Research on Physical Simulation Model Production and Remaining Oil Distribution Based on Fluvial Compound Sand Body Architecture

Summary Bohai offshore oil fields have reached the stages of high and ultrahigh water content, resulting in a significant amount of remaining oil within reservoirs after long-term waterflooding. For typical offshore oil fields characterized by wide well spacing and sparse well networks, the river facies composite sand bodies pose a challenge. It remains unclear how the configuration of these composite sand bodies affects the spatial sweep characteristics of injection agents, as well as the formation and distribution of residual oil. This study employs a seismic-guided method, integrating well logging and seismic data, to examine the stacking patterns of fluvial compound sand bodies in a typical offshore oil field. A 3D physical model of composite sand bodies with varying stacking relationships was established to carry out physical simulation experiments involving waterflooding and chemical flooding. This study aims to investigate how the interface and differences in the physical properties of composite sand body configurations affect the distribution of remaining oil. Results reveal that the stacking characteristics of fluvial compound sand bodies in the Bohai oil field are represented by three main configuration patterns—the abandoned river channel type, the side edge contact type, and the main body cutting and stacking type. Unlike the laterally structured compound sand body, the vertically superimposed compound sand body configuration in the target reservoir minimizes flow resistance and enhances the effectiveness of swept volume expansion. This ultimately results in improved recovery rates during both waterflooding processes. Furthermore, in a configuration featuring one horizontal injection well paired with two vertical production wells, the injection point benefits from a larger filtration area and a broader sweeping range. Nonetheless, there are difficult-to-sweep areas resulting in higher residual oil saturation. Utilizing a horizontal well arrangement allows for a larger permeable zone, which in turn minimizes the water-fingering effects. Following the waterflooding process, the water ridge at the injection side appears relatively gentle, while the wings at the production side are considerably steeper. Following waterflooding in the 3D physical models, the application of gel plugging combined with microsphere and surfactant profile control and flooding can effectively use the remaining oil. Polymer gel shows a good plugging effect on the high-permeability layer, significantly increasing injection pressure after plugging. This prompts the subsequent polymer microsphere and high-efficiency oil displacement agent to move into the residual oil enrichment area, improving oil recovery by 22.78–26.26% compared with waterflooding alone.