Investigation for the integration of associated produced gas into low tension gas floods

With increased environmental restrictions, flaring may no longer remain an option for dealing with produced hydrocarbon gas in the oil field. One possible solution for responsibly handling this gas is to reinject it into the reservoir through an injection well. Gas floods have long been used for enhanced oil recovery, however they oftentimes require miscible conditions within the reservoir. 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 is a promising tertiary oil recovery technology in low permeability reservoirs. This LTG process is a technique that involves either co-injection or alternating injection of gas as a mobility control agent to improve sweep efficiency, paired with an optimized surfactant formulation that is able to generate ultra-low interfacial tension (IFT) between the oil and aqueous phases. This reduced IFT allows for the previously trapped oil to become mobile and the added mobility control from the in-situ generated foam better allows for this mobile oil to exit the porous media. An experimental investigation of typically produced hydrocarbon gas was conducted through a series of tests including phase behavior tests, dynamic foam strength tests, and oil recovery corefloods. These tests were performed over a range of temperature, pressure, and salinity values. 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 for 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