Super critical carbon dioxide (SC-CO2) flooding is one of the most important enhanced oil recovery (EOR) methods to recover oil from both sandstone and carbonate reservoirs. In many cases this process is handicapped, especially in thick reservoirs, by SC-CO2 gravity override. SC-CO2 is lighter than oil and water, so there can be extensive gravity override of SC-CO2 bypassing oil in the lower part of the formation. Different methods have been used to control SC-CO2 mobility and improve its sweep efficiency by either increasing its density, viscosity, or reducing its relative permeability. SC-CO2 as a foam or as an emulsion is one of these methods and can provide better mobility control of the injected SC-CO2. This paper investigates the impact of various parameters such as liquid/liquid ratio, different foam qualities and different injection modes on the SC-CO2-foam quality and its rheological properties.

In this study, types of surfactants were used to generate SC-CO2-foam. SC-CO2-foam was generated at two different type of injection modes. Experiments were designed and conducted in a high pressure and temperature flow loop instrument to identify the optimum surfactant concentration and liquid/liquid ratio that can produce high quality foam and increase the SC-CO2 viscosity. During the experiment, SC-CO2-foam characteristics were analyzed through a visual cell in terms of bubble size distribution.

The rheological properties of the SC-CO2-foam were investigated by varying the shear rate, shear stress, foam quality, injection modes and foaming agent concentrations at reservoir conditions. The experimental results show that the foam mobility (total mobility of SC-CO2-surfactant solution) decreases with increasing foam quality. The results indicate that the SC-CO2-foam can make strong and stable foams under certain conditions. This was also correlated with the images of the high pressure, high temperature (HPHT) foams that were captured through microscope at different time intervals and analyzed to indicate their stability. Two foaming agents were identified that show excellent foam quality with good foam strength and stability over a period of time at reservoir conditions.

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