| dc.description.abstract | Switchable ethoxylated amine surfactants are readily soluble in CO2 and high-saline brines, as well as chemically stable at high temperatures. Additionally, in their cationic form, these surfactants exhibit low adsorption on carbonates, making them excellent candidates for EOR and other applications in high-salinity, high-temperature carbonate formations. This work focuses on investigating the foaming and interfacial properties of Ethomeen C12 (EC12) in presence of CO2. The objective is to optimize the surfactant concentration, pH, and brine salinity, and composition for maximizing the foamability and stability of CO2 foam at 150°F. From the results, potential applications of EC12 for CO2 foam in the oil/gas industry is recommended.
The various conducted foam tests helped determine the optimum parameters for CO2 foam stability at room temperature and at 150°F. The surface tension of EC12 as a function of concentration was evaluated using a drop-shape analyzer. From the surface tension versus surfactant concentration plot, the critical micelle concentration (CMC) and the slope were calculated. EC12 was prepared at a salinity range of 0-25 wt%, surfactant concentrations of 0.0001-1 wt%, and pH 2.5 and 6.5. The influence of cation charge on the foam stability was also examined using NaCl and CaCl2 brine solutions. The foam tests assisted in determining the optimal initial foamability and the foam half-life in different salinity, temperature, and pH conditions. The surface tension study illustrated the use of interfacial properties to evaluate the potential of the surfactant to create stable foam.
Maximum foam stability was observed for a solution comprising of 1.5 wt% EC12, 25 wt% NaCl, and pH 6.5. The foam stability was enhanced at high salinity conditions because of the increased interactions between the anions and the surfactant heads. The interactions allowed closer packing of the surfactant molecules at the lamellae and strengthening the foam. At a pH of 2.5, the absence of salt led to poor foam stability. However, in presence of NaCl, the foam was stable for longer periods of time because of the decreased repulsion between the surfactant heads. The surface tension study helped in validating the foam stability tests. The surface tension gradients were a direct indicator to the foam stability. There was a strong resistance to foam degradation when multivalent cations were present, up to 25 wt% multivalent salt concentration. However, in the presence of sulfate ions, the foam degraded very quickly. This was further evidence indicating strong performance of switchable ethoxylated amine surfactant in high-salinity conditions of 25 wt% NaCl. Extensive investigation of the foaming performance and interfacial properties of this surfactant type over a wide range of salinity and pH in representative field conditions was conducted. These are the gaps in the literature that this work addresses. Additionally, recommendations on optimizing the use of EC12 depending on the reservoir conditions are provided as a result of this study. | en |
