Abstract

Cretaceous oil reservoirs in Wyoming, many of which have been the target of unsuccessful cyclic CO₂ projects, are not inherently unqualified for this technique in spite of the poor performance of many of the projects. Various reservoir geological and aqueous geochemical aspects that have affected the success of some projects have been indentified. Five case studies are presented which illustrate how two of the problems of cyclic CO₂ projects, confinement and problems of scale precipitation, might be avoided. Confining the CO₂ to the near-wellbore region is essential to keeping the CO₂ in contact with residual oil there and moving it to the wellbore. Some features that may contribute to loss of confinement are high permeability heterogeneity, nearby injectors or producers, good reservoir continuity, and fractures. Scale problems are not likely during most cyclic CO₂ projects, but can be very damaging when they do occur. The combination of features likely to cause scale problems are a long CO₂ soak time, abundant calcite in the reservoir, and a large pressure drop into the wellbore. Many of these features can be evaluated from existing data.