LAUSR

Abstract Gas floods have long been used for enhanced oil recovery, however they often times require miscible conditions within the reservoir to be successful. If this reservoir has been depleted and no longer contains the internal pressure to achieve these miscible conditions, an enhanced oil recovery technique known as Low Tension Gas (LTG) may be a better alternative that has been proven to increase oil recovery. This LTG process is a technique which involves either co-injection or alternating injection of gas and an optimized aqueous surfactant solution to both improve mobility control and reduce the interfacial tension between the oil and aqueous phases. When paired with specifically selected surfactants, the injected gas will create an in-situ generated foam which increases the apparent viscosity and acts as a mobility control agent to improve sweep efficiency. The optimized surfactant formulation also has the ability to generate ultra-low interfacial tension between the oil and aqueous phases. This reduced IFT allows the previously trapped oil to become mobile and the added mobility control from the foam better allows for this mobile oil to exit the porous media. The impact of hydrocarbon gas as the co-injected gas was investigated and found to be not only compatible with, but ultimately beneficial to the LTG process. The use of hydrocarbon gas at elevated pressures had a notable impact on phase behavior by slightly lowering the optimum salinity, while significantly increasing the solubilization ratio. This increase in solubilization ratio corresponds to a lower IFT experienced between the oil and aqueous phases, leading to improved oil recovery. This investigation also noted that in the presence of Type I microemulsion, foams created using a hydrocarbon gas composition, appeared to produce a slightly lower foam strength than that of previously used nitrogen. However this slight decrease in foam strength was more than offset by the significant increase in solubilization ratio. Using different hydrocarbon gas compositions as the injected gas during a series of corefloods presented an increase in both the recovery rate and ultimate recovery. This suggests that repurposing produced hydrocarbon gas may not only be the environmentally responsible decision, but also economically advantageous as this may allow for a decrease in surfactant costs used within a Low Tension Gas flood while still achieving the same improved oil recovery.