Study On Profile Control And Flooding Technology Of Supercritical CO₂ Foam

As a flooding method, CO₂ has not only the general flooding mechanisms like general gas flooding, but also the mechanisms of physical chemistry features due to dissolving in water and crude. Mixing CO₂ and surfactant into CO₂ foam system, can control the mobility of CO₂ effectively, and play the double role of CO₂ flooding and foam flooding which may enhance oil recovery dramatically. Moreover, as the greenhouse gas, controlling CO₂ discharge and realizing CO₂ geological buried storage effectively is a huge challenge in front of the governments.This paper is starting from supercritical CO₂ physical features. Through the experiment, observed the state transformation of CO₂ under 55°C and different pressures (5²0MPa), found marked differences of CO₂ state during different ranges of pressure. Experimentized ScCO₂ foaming under 55°C and 9MPa situation, found that the state of ScCO₂ foam is like incanus emulsion, and stability is worse than N2 foam under the same experimental situation. Experimentized the migration law of ScCO₂ in porous media, analysed the impact of permeability, oil saturation, and saltness on diffusive equilibrium. Through theoretical derivation, combining the CO₂ foam state experiment, and bringing in the solubility in water of CO₂, gained a theoretical CO₂ foam state equation.Researched flow law of CO₂ foam flooding in porous media by aqueous core experiments. Analysed the impact of permeability, gas liquid ratio, and inject velocity on the plugging performance of CO₂ foam based on the physical features of ScCO₂. Found and explained the reasons of the change law of CO₂ foam resistance factor is different from N2 foam. Due to describe the diversion effect of CO₂ foam in parallel system, defined a concept called diversion number, and found that diversion effect is increasing with the increasing of permeability differential. Developed foam diversion theory based on the steady, uniphase and linear assumption. Brought in a concept which is called permeability difference to investigate the essential impact on the foam diversion effect and developed three equations on the basis of combining theory with practice.Researched flow law and oil displacement of CO₂ foam flooding in porous media by the microscopic experiments. Found foam generation mechanism and law of flow in porous clearly, and there is an upper limit and a lower limit velocity of gas for foam generation through theoretical analyzing, explained the microscopical mechanism in macroscopical phenomenon. Found the process of oil displacement by foam flooding, and the primary is that a huge bubble occupying the capillary tube, and summed up many mechanisms of CO₂ foam flooding.Researched the EOR effect of CO₂ foam profile control and flooding by comparison and impact factor experiments. The results shows that CO₂ foam can enhance oil recovery dramatically than water flooding, CO₂ flooding and WAG. On the basis of the water sensitivity feature of reservoir, used CO₂ foam/CO₂ (FAG) alternate flooding in the experiment. Researched the impact of foam injectivity, inject period and gas-liquid ratio of foam on EOR effect. Results shows that the three impact factors above influenced on EOR effect of CO₂ foam to varying degrees, and the essence is that the high-strength foam whether generated or not in the high-speed channel.