Evaluation of an Ethoxylated Amine Surfactant for CO2-Foam Stability at High Salinity Conditions

Abstract

CO2 flooding is well-known to be an effective EOR method and has been successfully implemented around the world. In heterogeneous formations, CO2 foam has been utilized to achieve conformance and mobility control. However, the foam performance degrades significantly at high saline environments. Ethoxylated amines have been reported to be successful in high pressure-high temperature (HPHT) conditions. This paper investigates the results obtained from a study of the foamability and foam stability at varying salinities, initial pH, and surfactant concentration. The surfactant is evaluated to provide optimum concentration, salinity, and a pH level for better foam performance during EOR applications. Bottle shake tests achieved the objectives of this paper. Different salinities of brine, ranging from 0 to 25 wt%, mixed with the surfactant, with concentrations of 0.1 to 1 wt%, helped in the investigation of the foam performance. The bottle shake tests were conducted to prescreen the surfactant concentration, salinity, and pH level, at ambient conditions. Sodium chloride was used to prepare the solutions. The bottle shake tests indicated that, in terms of foam half-life, the optimal surfactant concentration was 0.25 wt% for salinities of 0 to 15 wt% NaCl. Moreover, at this salinity range, the lowering of the surfactant solution's pH had a detrimental effect on the foam stability. The faster collapse of the foam at lower pH could be attributed to the repulsive interactions between the amine headgroups. The optimum initial pH was between 6 and 6.5 for salinity between 0 to 15 wt% NaCl. However, for higher salinity environment, 15 to 25 wt% NaCl, foam stability at low pH shows drastic improvement over its counterpart at lower salinities. At these high salinities, the optimal surfactant concentration was 0.50 wt%. The application of the ethoxylated amine surfactant at different salinity levels has not been studied in detail. The application of this surfactant needs to be evaluated for optimum concentration, pH, and salinity. The effect of the surfactant's initial pH on the foamability and foam half-life has not been investigated. This paper addresses these gaps in literature and provides an optimized composition that can be applied for EOR operations.