In this paper, an easily computable algorithm, allowing the calculation of the minimum miscibility pressure (MMP) whatever the displacement mechanism, is described. Such an algorithm is based on a multiple mixing cell calculation without any porous media. Only thermodynamic equations are taken into account i.e., a P/T flash routine is only required. Computational speed is from 15 to 80 times faster than using a commercial one-dimensional (1D) simulator, but the accuracy is the same.

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Gas injection processes are among the most effective methods for enhanced oil recovery. A key parameter in the design of a gas injection project is the minimum miscibility pressure (MMP), the pressure at which the local displacement efficiency approaches 100%. From an experimental point of view, the MMP is routinely determined by slim tube displacements. However, because such experiments are very expensive (timeconsuming), the question we want to answer in this article is as follows: Is this still necessary to measure the MMP? In other words, may other quicker, easier and cheaper gas injection experiments such as swelling test or multicontact test (MCT) substitute for slim tube test? This paper concludes that when the injected gas is not pure CO 2 (and probably not pure N 2 or pure H 2 S), it is enough to fit only two parameters of the equation of state on data including classical PVT data + swelling data + MCT data and then to predict the MMP. The accuracy obtained is similar to the experimental uncertainty. It is thus possible to conclude that the slim tube test may be replaced by swelling tests and MCT, which are much cheaper.

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In this paper, real crude oils are dealt with which are modeled with an average of 30 components. On the selected examples, neither the initial tie line, i.e., the tie line that extends through the original oil composition, nor the gas tie line, i.e., the tie line that extends through the injected gas composition, controls the miscibility process. In any case, the miscibility process is controlled by one of the (nc − 3) crossover tie lines, if nc is the number of components in the crude oil. However, it is shown that the miscibility process may be a pure vaporizing gas drive mechanism (VGDM). To be more precise, it is shown that a mixed condensing/vaporizing mechanism may, with increasing pressure, turn into a pure VGDM. This means that the classical definition of a VGDM, i.e., the lowest pressure at which the initial tie line is critical, must be changed. This is the main point of this paper. In the case of a VGDM controlled by a crossover tie line, the MMP (the lowest pressure at which the key crossover tie line becomes critical) may still be computed by a one cell simulation algorithm. Another aim of this paper is to explain what really happens during a one cell simulation and to give proof that such an algorithm may not make critical the initial or the gas tie line.