An experimental study on oil recovery performance using in situ supercritical CO_2- Emulsion for carbonate reservoirs

The poor volumetric sweep efficiency for secondary and tertiary oil recovery processes is mainly caused by reservoir heterogeneity, whether sandstone or carbonate reservoirs. Reservoir heterogeneity is usually characterized by permeability anisotropy and permeability contrast of the formation. Because of the problems of permeability anisotropy and permeability contrast of low and high permeable zones, most of displacing agents are injected into the high permeable zone. When the displacing agent is produced from production well, the displacing efficiency is extremely ineffective. In other words, large quantities of oil remain in the low permeable zone, which is un-swept by displacing agent. In this study, we used In-Situ sc-CO_2-Emulsion as a conformance control agent to plug the high permeable zone, and then improve the volumetric sweep efficiency of the low permeable zone in a carbonate formation. To achieve this goal, we studied the effect of two types of conformance control patterns on tertiary oil recovery performance by sc-CO₂ miscible injection for carbonate reservoirs at reservoir conditions. The conformance control patterns are classified as follows: (1) isolated the low permeable zone and opened the high permeable zone, and (2) opened both the low and high permeable zones when a base-gel system was injected into the core plugs after initial sc-CO₂ flooded. Two physical models consisted of carbonate core plugs set up initially to carry out the core flooding experiments of displacing oil and obtained the remaining oil saturation by water flooding as a secondary oil recovery process. The preliminary sc-CO₂ injection was conducted following water flooding to recover the remaining oil after water flooding as a tertiary oil recovery mode. The practice of the conformance control patterns using In-Situ sc-CO_2- Emulsion generated by injecting base-gel system into the core in which had the presence of sc-CO₂ was performed after the preliminary sc-CO₂ injection. The second sc-CO₂ injection was conducted following base-gel system injection. All experiments were under reservoir conditions. The base-gel system used in this study consisted of polymer and surfactant. The experiments of stabilization and apparent viscosity measurement of the base-gel system and CO₂ emulsion were conducted at varying experimental conditions. Based on the results and observations of the characteristics of study on the base-gel system and CO₂ emulsion, core flooding experiments, the practice of the conformance control patterns with in-situ sc-CO_2- Emulsion, and second sc-CO₂ miscible injection, the in-situ sc-CO₂ emulsion was generated successfully in the formation in which was the presence of sc-CO₂. The volumetric sweep efficiency and oil recovery under the conformance control patterns using in-situ sc-CO₂ emulsion was improved for both physical models. Also, the production performances were compared for both physical models before and after base-gel system injection in this paper.