Sour Gas Injection to Enhance Oil Recovery

Abstract

Proper handling of sour gas produced is crucial to the development of sour reservoirs. Over years of research and practice, many methods of sour gas processing have been developed from the solid storage of sulfur to reinjecting the sour gas back into producing or depleted light oil reservoir for miscible flooding enhanced oil recovery. This paper seeks to investigate the use of sour gas to enhance oil recovery and its associated phase behavior problems. In designing a miscible gas flooding project, the minimum miscibility pressure (MMP) is the key parameter that determines the impact on gas and oil mixing phase behavior. The MMP is the lowest pressure at which the displacement process becomes miscible upon contact with the reservoir fluid. There are various methods to determine the MMP. A laboratory experiment is the most accurate but time consuming and subject to fluid sample quality; while the Equation of State is poor in characterizing polar molecules like H2S. For this study, empirical correlations are used to determine the MMP because the study focuses more on the general trend of how methane concentration affects the MMP of the process. In this study, a sour gas injection model is developed using a compositional simulator with the aim to determine mechanistically how sour gas enhances oil recovery. This model is used to evaluate the effect of some important parameters such as acid gas concentration, injection pressure and injection rates on oil recovery efficiency. The result of MMP study shows that methane concentration has a significant impact on the MMP of the process. As methane concentration increases in the injection gas, the MMP of the process also increases. From this study, it was observed that increasing acid gas concentration decreases the MMP of the process as a result of an increase in gas viscosity, consequently extending the plateau period resulting in late gas breakthrough and increasing the overall recovery of the process. It is also seen that this increase in viscosity increases the volumetric sweep efficiency of the process which is an improvement to most gas injection enhance oil recovery (EOR).