On the importance of gravity and three-phase flow in gas displacement processes

This review paper examines the roles of gravity and capillary forces in determining the efficiency of oil recovery by gas displacement. Gas injection in either miscible or immiscible forms can be designed to achieve attractive additional oil recovery, following water injection, or in combination with water injection (WAG). Factors influencing the selection of three-phase flow correlations and the advantages to be derived by using gravity to benefit the displacement are discussed. The use of nearly miscible displacement with gravity assistance can have attractions which provide opportunities for optimal selection of enrichment and water/gas ratios. Uncertainties associated with modeling the effects of heterogeneities are indicated, and some results given on the benefits of gravity for gas displacement in reservoirs with vertical fractures. Some future research needs are summarized.