Miscible flooding was invented many years ago, and in the 1950's it was viewed as one of the most promising techniques to use for improving oil recovery from a reservoir.1,2,3,4,5,6,7 Since that time many groups have researched what would be the most important parameters to optimize in the lab, have developed theoretical models to correlate these parameters, and then have implemented these "optimally designed" gas injection systems in the field. Amidst all the increase in technology and sophistication there is still ongoing debate as to whether one needs to achieve miscibility in order to optimize the recovery or whether a degree of immiscibility, characterized by the name "near miscible", is equally adequate for field implementation in enhanced oil recovery processes.
This paper seeks to provide insight into these questions by reviewing some of the parameters which are at work in gas injection EOR as well as qualifying some of the techniques which can be used in designing gases for injection. Moreover, case histories are described herein where laboratory work was performed, phase behavior described, and then the gas injected into the reservoir. Results from the field are then shown and commentary included on the field performance.