Microscopic Residual Oil Distribution Characteristics and Quantitative Characterization of Producing Degree Based on Core Fluorescence Analysis Technology

Abstract

In this study, to address the insufficiency of research on the distribution characteristics and quantitative characterization of oil, water, and rock in a reservoir, laser confocal and core fluorescence analysis techniques are combined with core flooding experiments to investigate oil–water distribution characteristics in the core and the microscopic origin of residual oil. The results obtained show that the three-dimensional (3D) distribution characteristics of oil, water, and rock can be depicted using a laser confocal technique. Free and bound states are dominated by water flooding, and their total proportion is 93.65%, while the semibound state only accounts for 6.35% of the total. Polymer flooding has clear effects such as production of cluster-like residual oil, interparticle adsorption state residual oil, pore surface oil film, and corner residual oil. After alkali-surfactant-polymer (ASP) flooding, the residual oil produced at the lowest degree corresponds to particle adsorption oil, pore surface oil films, and interparticle adsorption state residual oil. The emulsion transition process in porous media, i.e., Winsor I→Winsor III→Winsor II, is studied. Moreover, the fluorescence analysis technology is used to clarify the causes for residual oil production, namely, pore structure, crude oil viscosity, the Jia Min effect, particle migration, and adsorption capacity. The combination of laser confocal and fluorescence analysis technology can help realize the three-dimensional reconstruction of the fluid in the core, and it can quantitatively characterize the microscopic residual oil. According to the analysis results, it can also guide the formulation and adjustment of oilfield development plans.