In recent years, the application of CO2-foam in mobility control has gained more interest among surfactant-based enhanced oil recovery processes. This is because the mobility-controlled CO2 flood can mitigate the problems of frontal instability as well as the preferential flow of CO2 in a heterogenous reservoir which otherwise induces the early breakthrough of CO2.
Earlier laboratory results indicate that the changes of flow and displacement behavior of CO2-foam can reduce the mobility of CO2 alone and increase the displacement efficiency. Further measurements of the mobility of CO2-foam in several researches also confirm the mobility-reducing characteristics of CO2-foam. In a recent paper, Lee et al. suggested that if a suitable surfactant is selected and a careful design is implemented, a mobility-controlled CO2-foam flood can not only preserve the uniformity of the flood front but also correct the nonuniform flow in a heterogeneous reservoir to some extent. Therefore, the objective of this study is to extend our earlier versions of the experimental designs to evaluate the surfactants for mobility controlled CO2-foam flood applied in a particular reservoir.
In this study, the selected target reservoir consists of dolomite limestone formations. The candidate surfactants include commonly used anionic and nonionic types of foamant. From an economic standpoint, it is advantageous to use the lowest concentration of surfactant possible. Accordingly, the effectiveness of all candidate surfactants are evaluated at concentrations below their CMC.
Although we are interested in surfactant concentrations below their CMCs, the selected surfactant still needs to be effective in 1) reducing the mobility of CO2-foam to some extent, 2) resisting chemical or temperature degradation, 3) enduring the presence of dissolved salts at high concentrations, and 4) not being adsorbed excessively onto the rock.