Measurement of Bubble Point Pressures of n-Decane, CO₂ and N₂ Mixtures

Utilization of carbon dioxide in enhanced oil recovery (EOR) serves two important goals. Firstly, it recovers more oil, which could not be recovered during primary and secondary recovery methods. Secondly, it is one of the carbon capture and sequestration (CCS) techniques that work to reduce the emissions of greenhouse gases into the air and combat the climate change. To design and optimize the process of CO2-EOR, it is crucial for engineers to have knowledge about the reservoir fluids properties and their interaction with injected gases. Bubble point pressure is critical for the description of the reservoir fluid behaviour. Constant composition expansion (CCE) experiments were performed to measure the bubble point pressures for binary mixtures of n-decane/carbon dioxide (n-C10/CO₂) and ternary mixtures of n-decane/ carbon dioxide/nitrogen (n-C10/CO₂/N₂). The n-decane represented the hydrocarbon phase, where the gaseous phase consisted of CO₂ and N₂. The experiments were conducted at two different temperatures, 30 and 60° C. The gas mole fraction in each mixture ranged from 20-80%. For the gaseous phase itself, N₂ and CO₂ were mixed in three different proportions: 0, 10 & 20% N₂ mole fractions. The work in this paper was set to examine how the bubble point would behave due to presence of nitrogen contamination in carbon dioxide, rise in temperature and changing mixture compositions. The results shows that bubble point pressure increased when the temperature increased from 30° to 60° C, for all mixtures. These increases in bubble point pressures ranged between 19-35%. The introduction of N2 into the mixture would raise the bubble point by up to 55%. The addition of more hydrocarbon into the mixture decreased the bubble point. Bubble point pressure is a strong function of gas solubility, which is capable to explain these behaviors of bubble points.