Phase Behavior In Miscible Systems Of Solvent, Dry Gas And Oil

Abstract

Introduction In solvent injection projects, the injection fluid mixes with the reservoir oil being displaced. As the project proceeds, all the possible mixtures of reservoir oil and injection fluid from pure oil to pure injection fluid will occur. If all these mixtures are single phase at reservoir temperature and pressure, then the process is a miscible displacement, and high oil recovery can be obtained from the swept regions of the reservoir. In most cases, the injection fluid is vaporized at reservoir conditions. Therefore, for a miscible displacement, it is necessary to have a composition transition from liquid reservoir oil to vaporized injection fluid without having two phases present at any one point in the reservoir. A series of phase behavior experiments was conducted which showed the event which occur during the transition from pure reservoir oil to pure injection fluid. These events can be illustrated by Fig. 1. Fig. 1 shows that the addition of injection fluid to reservoir oil produces a series of bubble point mixtures, then a critical mixture, and finally, a series of dew point mixtures. A bubble point mixture is defined as one which produces a gas as the second phase when the pressure is lowered into the two phase region. A dew point mixture produces a liquid as the second phase.