Estimation of minimum miscibility pressure (MMP) of CO2 and liquid n-alkane systems using an improved MRI technique.

Minimum miscible pressure (MMP) of gas and oil system is a key parameter for the injection system design of CO2 miscible flooding. Some industrial standard approaches such as the experiment using a rising bubble apparatus (RBA), the slim tube tests (STT), the pressure-density diagram (PDD), etc. have been applied for decades to determine the MMP of gas and oil. Some theoretical or experiential calculations of the MMP were also applied to the gas-oil miscible system. In the present work, an improved technique based on our previous research for the estimation of the MMP by using magnetic resonance imaging (MRI) was proposed. This technique was then applied to the CO2 and n-alkane binary and ternary systems to observe the mixing procedure and to study the miscibility. MRI signal intensities, which represent the proton concentration of n-alkane in both the hydrocarbon rich phase and the CO2 rich phase, were plotted as a reference for determining the MMP. The accuracy of the MMP obtained by using this improved technique was enhanced comparing with the data obtained from our previous works. The results also show good agreement with other established techniques (such as the STT) in previous published works. It demonstrates increases of MMPs as the temperature rise from 20 °C to 37.8 °C. The MMPs of CO2 and n-alkane systems are also found to be proportional to the carbon number in the range of C10 to C14.