Abstract Miscible gas flooding has been used for enhanced oil recovery for many years. Considerable data exists for CO2 and enriched hydrocarbon flooding so that screening criteria can be applied to determine when miscible flooding with these gases could be successful. However, for nitrogen the data are much more sparse. Thus, previous screening tools are very imprecise. In fact, all four correlations for nitrogen minimum miscibility pressure available in the literature predicted miscibility pressures that were more than 1000 psi different from the measured value for more than a third of the data available in the literature.
This paper presents a new much more accurate correlation for nitrogen MMP. This correlation takes into account the effects of oil composition and reservoir temperature and matches all nitrogen MMP data in the literature within 750 psi. This correlation predicts that the nitrogen MMP of an oil decreases as the methane or intermediate content of the oil increases, and that the nitrogen MMP increases as the mol weight of the oil increases. It also shows that the nitrogen MMP goes through a maximum as the temperature increases and that this maximum is a function of oil composition.
In addition, this paper summarizes available nitrogen MMP data and presents seven new data points.
Introduction The oil industry has been involved in miscible gas flooding for many years. Most of the industry's experience has been with CO2 in the United States and with enriched hydrocarbon gas in Canada. Because these gases may not always be available outside of North America and since many international reservoirs are at relatively high temperatures and pressures, there has been an increased interest in using nitrogen as a miscible solvent.
Theoretically nitrogen would be available almost worldwide, but the pressure required for nitrogen to become miscible with crude oils is quite high. Minimum Miscibility Pressures (MMP) on the order of 5000 to 6000 psi for North Sea oils and values as high as 9000 psi for an Alaskan oil have been reported in the literature.
The use of nitrogen as a miscible solvent has not been as extensively studied as either CO2 or enriched hydrocarbons. Therefore there are really no good screening criteria sufficiently useful to guide an engineer in making a decision as to whether or not nitrogen could be used as a miscible solvent. The purposes of this work were to:To build an apparatus capable of measuring nitrogen MMP at pressures up to 10,000 psi and temperatures up to 300 degrees F.
To determine the effects of oil composition and temperature on nitrogen MMP.
To develop a nitrogen MMP correlation based on these parameters which can be used as a screening tool to help decide if nitrogen miscible flooding is feasible.
Background There are very few measurements of nitrogen MMP reported in the literature. Most of the data for nitrogen MMP involved relatively light oils with high methane concentrations (anywhere from 30 to 60 mol%) and low C7+ mol weights (less than 200 g/mol).
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