Application of Foam for Mobility Control in Enhanced Oil Recovery (EOR) Process

This thesis focuses on the application of foam for mobility control in enhanced oil recovery (EOR) process. The performance of foam and surfactants was evaluated by systematic laboratory study. This includes the screening and evaluation of surfactant formulations for foam EOR process and the investigation of foam for mobility control at reservoir conditions. The adsorption of cationic surfactants on natural minerals was discussed in a separate chapter, although it is one aspect for evaluating surfactant formulations. A numerical model was used to fit the foam strength for foam flooding at reservoir conditions. The solubility, thermal and chemical stability and foaming ability of surfactant formulations were investigated in the screening and evaluation step. A qualified surfactant formulation for foam EOR should be soluble and stable from injection to reservoir conditions. The foaming ability of surfactant formulations needs to be verified in a porous media with crude oil. The bulk foam tests, i.e., foam height, equilibrium foam volume and foam half-life, are not suggested to be used for evaluating foaming ability of surfactant formulations, because of the poor correlation with foam tests in porous media. The detrimental effect of oil, especially for light crude oil, for foam stability was demonstrated. Foam boosters, e.g., betaine surfactants, can be used to stabilize the foam in the presence of crude oil. The mobility control ability of foam was evaluated in Silurian dolomite cores at reservoir conditions after screening and evaluation step. The apparent viscosity of foam was used to describe the mobility control ability. The higher apparent viscosity indicates the stronger foam and better mobility control ability. The strength of foam depends on foam quality, salinity and temperature. The influence of each parameter was investigated and illustrated by controlled experiments. Ethomeen C12 in formation brine and CO2 can generate strong foam at 120 °C and 3400 psi in a wide range of foam quality after the pressure gradient exceeded the minimum pressure gradient. The adsorption of cationic surfactant on the pure carbonate minerals is low owing to the repulsion of the electrostatic force. However, the natural carbonate minerals contain negatively charged impurities, e.g., silica and clays. The adsorption of cationic surfactants on these impurities was significant. Multivalent cations, i.e., Mg2+, Ca2+ and Al3+, can compete with cationic surfactants on the negatively charged binding sites to reduce the adsorption. The adsorption of Ethomeen C12 on silica was reduced from 5.33 mg/m2 in DI water to 3.31 mg/m2 in synthetic brine with 1.51×10-3 mol/L Al3+. The adsorption of Ethomeen C12 was measured at 2 atm CO2 to keep the solution clear. The method of methylene blue (MB) two-phase titration was improved to determine the cationic surfactant concentrations in high salinity brine. In summary, this study demonstrates the methodology to screen the surfactant formulations for the foam EOR process, elucidates the application of the foam for mobility control at reservoir conditions, improves the MB two-phase titration for cationic surfactant in high salinity brine and illuminates the reducing of the adsorption for cationic surfactants on natural carbonate minerals