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 consideration 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 mow 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.


With the vicissitudes in the oil industry, many times enhanced oil recovery schemes are reviewed with an optimistic or pessimistic attitude. It commonly seems that there is no middle ground. The thought of high initial costs associated with enhanced oil recovery schemes sometimes dissuades some operators from considering what may be their only hope. Whereas, at other times, larger corporations, because of the "charisma" associated with high technology implementation, have spent money needlessly on EOR schemes which from the beginning were not suited to their application.

Take, for example, the winter of 1994–95. Gas prices were low and therefore the production of energy from reservoirs was of much greater value when obtained as a liquid phase rather than as a gas. At times like this, it would be synergistic to have a reservoir where one knows that gas injection would be beneficial and thus have an idea of what is the optimal gas design. Indeed, many companies considered shutting in their gas production and some did reduce gas production due to gas prices. Some of the gas could be used for injection into reservoirs which were declining in productivity. It is important that the research needed to identify good gas injection candidates must be synchronized so that when an opportunity arises, one can apply the principle of serendipity and make these market conditions work for you.

No matter what the history of gas injection has been, which is viewed with different conclusions depending upon to whom you speak, the question still remains of what is the best way to optimize cash flow from a given reservoir.

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