Evaluation of Surfactants for CO₂-Foam Mobility Control

The effectiveness of surfactants, for C0₂-foam mobility control in dolomite limestone formations, is evaluated at surfactant concentrations below their critical micelle concentra-tions (CMC). The candidate surfactants are commonly used foamants which are either nonionic or anionic types of surfactants.

The evaluation procedures to be discussed, and the data to be presented, include the determination of foamability of surfactants and foam durability of C0₂-foam, the measurements of adsorption parameters of surfactant onto reservoir core samples, and the measurements of C02-foam mobility in reservoir rock samples. All of the experiments except the adsorption measurements are conducted at reservoir conditions. Adsorption of surfactant onto reservoir rocks is measured using a modified drop-weight method in a direct flow-through measurement at ambient conditions.

The C0₂-foam activities are found to be affected by the presence of crude oil in the foam durability test. However, C0₂-foam mobilities are still reduced effectively inside the rock samples containing some residual oil. It is also found that an additional amount of surfactant over the surfactant concentration required for C0₂-foam propagation is needed to satisfy the permanent adsorption. At surfactant concentrations below the CMC, the effectiveness of mobility reduction of C0₂-foam as well as the amount of surfactant adsorption vary with the type of surfactant and its concentration in reservoir brine.

Through the entire evaluation procedures, the best candidate surfactant and the most suitable concentration are determined for a particular rock sample at a certain reservoir condition.The laboratory evaluation procedures can be carried out in relatively uncomplicated fashion and are applicable to different reservoir conditions.