Experimental Evaluation of Zwitterionic and Cationic Surfactants to Optimize Bulk Foam Properties for Gas Mobility Control in High-Salinity Carbonates

Abstract

Foam injection has been acknowledged as a promising technology to control gas mobility by establishing the flow resistance during gas enhanced oil recovery (EOR) processes. For applications in challenging carbonate formations, the development of well-matched foaming agents is required. In this paper, the foam performance established by different switchable and zwitterionic surfactants along with their combinations in controlling gas mobility and displacing the residual oil is investigated. The stable solutions of commercial amine-based and/or zwitterionic surfactants were prepared in 20 wt % salinity. A series of foamability and foam stability tests were conducted as initial screening at high temperatures in the presence and absence of crude oil. Foam texture and foam stability were also investigated at different gas/liquid fractions under high-temperature and high-pressure conditions. The best-performing formulation at optimum foam quality was evaluated in coreflooding experiments in terms of mobility reduction factor (MRF) and residual oil recovery. Bulk foam results demonstrated the superior foamability and foam stability of a betaine (B1235) surfactant. Foam endurance of B1235 was found comparable to the diamine (DTTM) produced foam; however, the DTTM surfactant showed insignificant foamability. Among all tested surfactants and their mixtures, B1235 was found most effective in maintaining foam properties in a crude oil environment, and no synergistic effect was observed in the use of surfactant mixtures. The optimum concentrations for B1235 with and without crude oil were 0.25 and 0.5 wt %, respectively. The results obtained from the experiments in a pressurized view cell indicated a prolonged decay profile at 90% gas fraction in bulk. During dynamic flow in carbonate rocks, the optimum quality of foam stabilized by the selected surfactant was found at 70%. At this quality, the pregenerated foam injection pronouncedly increased the MRF to 48. The cumulative oil recovery after foam injection was 67%, providing 25% incremental recovery. The overall performance of the betaine-based surfactant-stabilized foam in high-salinity carbonates was found effective in controlling the gas mobility during the foam EOR process.