A Laboratory Investigation Confirms the Relative Inefficiency of True Miscible Drives, and Outlines New Concepts for Maximizing Oil Recovery by Gas Injection

Abstract

Abstract Laboratory displacements of oil by gas at high temperature and pressure have been performed in one and two dimensions using both performed in one and two dimensions using both simple ternary mixtures and actual reservoir fluids. The results have been analysed with the help of a numerical model. The displacements carried out in the so called "dynamic miscibility" conditions are fundamentally different from true miscible displacements, in particular the conformance appears to be much better when optimum conditions (pressure and/or gas compositions) are selected. These conclusions may be extended to all displacement processes involving mass transfer between phases. Introduction Several types of displacement processes are commonly referred to as "miscible", although they do not involve identical thermodynamic conditions. Fig. 1 represents the classical ternary diagram, in which complex hydrocarbon mixtures are schematically described as a combination of three main constituents: methane (C1), intermediate hydrocarbons (C2 to C6) and heavy hydrocarbons (C7+). Although this diagram is only a crude approximation of the complex PVT behaviour of natural hydrocarbon mixtures, it is very convenient and good enough qualitatively for demonstration purposes.