ENHANCED OIL RECOVERY USING MIXED CO2/N2 FOAM IN SANDSTONE RESERVOIR

Increase in oil prices and difficulties associated with new discoveries for oil and gas have generated tremendous interest in enhanced oil recovery (EOR). Primary and secondary oil recovery can recover 30-40% of the original oil in place and almost 60-70% of the oil is trapped in the reservoir. It is strategic to focus on recovering oil from proven reserves by using different EOR methods. Among the many EOR processes, gas injection has been widely used for oil displacement and for maintaining pressure in EOR processes. Unfortunately, gas injection techniques suffer from high mobility and gravity override, which decreases the macroscopic sweep efficiency and ultimately the oil recovery. Foams can counter these problems by reducing gas mobility and gravity override, which significantly increases the macroscopic sweep efficiency and results in a higher recovery. CO2 and N2 gases have been commonly used in foam EOR processes. The inherent differences in CO2 and N2 result in variations in the properties of the foam formed from these gases. These differences are exacerbated with increases in pressure, especially at supercritical pressure (for CO2, 1,100 psi at 30C), because CO2 is unable to generate foam or generates weak foam. However, N2 remains in the subcritical state and generates strong foam even at higher pressures. The inability of CO2 to generate foam or strong foam increases mobility, which leads to a poor sweep efficiency. These difficulties can be overcome by replacing a portion of the CO2 with N2 because mixtures of N2 and CO2 gas can generate foam. Although many researchers have independently investigated EOR by using CO2 or N2 foam, the effects of mixed CO2/N2 foam on EOR have not been investigated. The objective of this project is to evaluate the performance of CO2/N2 foam at supercritical conditions for EOR from sandstone reservoirs. This project aims to maximize the sweep efficiency by generating CO2 foam under supercritical conditions by mixing N2 with CO2. A series of core flood experiments will be performed by co-injecting different proportions (ratios) of CO2/N2 mixtures with a surfactant solution. The results will be analyzed to optimize a range of parameters, such as the injection rate, foam quality, CO2/N2 ratio and surfactant type and concentration. The observations from this study will strengthen the potential application of CO2 foam in EOR and will generate data regarding the use of foam with different proportions (ratios) of CO2/N2, including low, medium and high ratios. This investigation will evaluate the prospect of using CO2 in EOR and will contribute to CO2 sequestration in the underground formation.