PETROLEUM SOCIETY OF CIM and CANMET PAPER NO. 95-51 "DOES MISCIBILITY MATTER IN GAS INJECTION?" F.B. Thomas, Hycal Energy Research Laboratories Ltd. T. Okazawa, Imperial Oil Resources Ltd. Adel Erian, Hycal Energy Research Laboratories Ltd.

Over the years gas injection design has undergone an evolution in the types of laboratory tests used to design a gas injection project as well as the interpretation of the experimental testing. In the recent past, there has been much written in the area of immiscible and near-miscible gas flooding. Often, some of these applications appear to be very effective and somewhat less expensive than the so-called "miscible " floods. In this paper the authors discuss some of the considerations which are germane to gas injection and provide evidence that suggests that many of the previously accepted laboratory techniques were not really providing what they were intended to. It is important that one understands the significance of these considerations when designing a gas injection project. The authors indicate that specific testing can be made to gain insight into the most important features of a gas injection project which concerns the interaction between the level of interfacial tension and the mobility effects. By appropriately quantifying whether a reservoir is going to be IFT or mobility-dominated, the operator can concentrate on designing a gas to optimize the factor which is dominant. It is important to know what that dominant factor is so that gas injection processes are the best that they can be. In answer to the question asked in the title of this paper, the authors suggest that most gas injection projects would involve a gas which exhibits properties in the so-called "near-miscible" range. Techniques for determining how miscible one needs to be are provided in this paper