Experimental Evaluation of Amphoteric and Switchable Surfactants for Improving Foam Performance Under Harsh Reservoir Conditions

Abstract

Foam injection is designed to reduce the effects of high reservoir heterogeneities and fluid viscosity contrasts during gas flooding, and hence, improve sweep efficiency. However, harsh reservoir conditions in the Middle Eastern reservoirs pose a serious problem to foam stability, leading to a poor mobility control for foam injection. In this study, different surfactant types and their combinations were tested to screen and optimize foam performance in harsh salinity (20 wt%) at high pressure and high temperature (HPHT) conditions (1000 psi and 80 °C) based on series of bulk foam experiments. For this purpose, different commercial amphoteric and amine-based switchable surfactants were utilized and their compatibility in 20 wt% brine were ensured at HPHT conditions. Initial screening was performed by conducting series of foam stability and foaming ability tests at high temperature. The surface tension and surfactant solution rheology tests were performed to analyze foam behavior. The mixtures of amphoteric and amine-based surfactants were then investigated to improve bulk foam performance. Foam stability and foam texture at different foam qualities under HPHT conditions were also studied. Bulk foam experiments showed that betaine (B-1235) surfactant outperformed other surfactant types through achieving the highest foam generation with excellent foam stability performance. Betaine foam endurance was found to be comparable to that of viscoelastic diamine surfactant. However, poor foam generation was observed when diamine was used as a single surfactant. The optimum concentration for betaine surfactant was found to be 0.25 wt%. A mixture of betaine and amine-based surfactant improved the latter foam properties and its performance was found to be higher than that of single surfactant. The foam stability of mixed surfactant was approximately 8 folds higher than that of single amine-based surfactant. Furthermore, foam texture directly controls foam decay profile, and the optimum foam quality based on static pressurized foam cell test was found to be 90% due to the formation of uniform and closely packed bubbles. This research identified high performing individual as well as a mixed surfactant systems for designing foam EOR projects for Middle Eastern harsh reservoir conditions.