Pore-scale investigation of supercritical multi-component thermal fluid flooding in deep heavy oil reservoirs

Abstract

Supercritical multi-component thermal fluid (SCMTF) flooding, which is an innovative technology for the development of deep heavy oil reservoirs, characterized by its high heat-carrying capacity, enhanced miscibility, and environmental sustainability, includes supercritical water (SC-W), supercritical carbon dioxide (SC-CO₂), and supercritical nitrogen (SC-N₂). Due to the existence of various mechanisms such as heavy oil component reactions, coking, miscible phase interaction, and multi-component synergistic effects during the SCMTF displacement process, the microscopic interaction mechanisms at the pore throat level are extremely complex. Currently, there is a lack of effective simulation means in this regard. This work has developed a pore-scale modeling workflow for SCMTF flooding. Firstly, a multi-component molecular model of heavy oil was developed to determine the diffusion coefficients of SCMTF in heavy oil. Subsequently, a numerical simulation model characterizing the reaction of heavy oil in a supercritical water atmosphere is established. Finally, a rapid conversion process from porous media images to models was established to characterize the influence of coke deposition on rock pore structure. In addition, the influence of reservoir and fluid properties on the oil displacement efficiency of SCMTF was analyzed. The accuracy of the model has been proven by comparing with experiments or analytical solutions. The results indicate that: The increase of SC-W and SC-CO₂ will increase the diffusion coefficient of SCMTF and heavy oil. A higher Péclet number results in weak miscibility between the injected fluid and heavy oil. The increase in permeability contrast will destroy the stability of the displacement front and lead to a decrease in recovery. As the reaction time increases, the light components content in heavy oil increases, and coke begins to be produced after 110 min, reducing the permeability and porosity of the rock. The increase in reaction temperature will reduce the light components content.