Completed Research
A Thermodynamic Correlation for the Minimum Miscibility Pressure of Carbon Dioxide Flooding of Petroleum Reservoirs
Robert Michael Enick, PhD, 1985
(Abstract: UMI Dissertation Publishing)
A thermodynamic correlation for the minimum miscibility pressure of carbon dioxide flooding is introduced in which the minimum miscibility pressure is estimated as the cricondenbar of a pseudo-binary system at reservoir temperature. The two components of this system are: (1) the displacing fluid and (2) the displaced crude, where the pentane and heavier fraction is modeled by a single alkane of equivalent average molecular weight. The effects of reservoir temperature, C5+ average molecular weight, the type and amount of CO2 impurities and any light or intermediate gases present in the oil are all accounted for. The oil molecular weight distribution is not, however.
The correlation is generated using the Peng-Robinson equation of state and is presented in a graphical form in which the contribution of each factor is individually evaluated. With the exception of a low temperature, high molecular weight correction, the correlation is independent of a CO2/crude oil minimum miscibility pressure data base.
Exact agreement between the cricondenbar and the minimum miscibility pressure is achieved for a model binary system, CO2/nC13H28, over the range of reservoir temperature. The Peng-Robinson equation of state can be used to predict the values exactly only if a temperature dependent interaction parameter is incorporated. Very good agreement of ± 3% is obtained between the minimum miscibility pressures and cricondenbars when CO2 impurities of 5% methane, 10% methane and 5% nitrogen are introduced. The equation of state predictions for the cricondenbars are as much as 30% low, however. When tested against 157 minimum miscibility pressure values for systems containing crude oil, the ratio of the predicted MMP to the actual MMP is 1.09, with a standard deviation of 19%. These results are comparable to many of the purely empirical correlations developed from a MMP data base of CO2/crude oil systems.
Unlike other correlations, a decrease in MMP with temperature is predicted at elevated temperature. This may have a favorable influence on very deep reservoir projects or CO2/steam flooding of reservoirs containing viscous oils.