Stability and mobility of foam generated by gas-solvent/surfactant mixtures under reservoir conditions

Surfactant-alternating-gas injection, where foam generation can be expected, is a feasible approach for improving the sweep efficiency of solvent flooding by increasing the apparent viscosity of gas solvent. The foam stability plays an important role in this process. In this study, the foam stability and mobility of solvent/surfactant/pseudo-heavy-oil system under reservoir condition has been examined experimentally. The following factors are considered in the static foam stability experiments: surfactant concentration, salinity, temperature, the presence of pure n-C16H34 as pseudo-heavy oil, and two types of gases (CO2 and C3H8). During the static experiments, foam is generated by sparging C3H8 or CO2 at a constant flow rate through the surfactant Triton X-100 solution, and then stirring the mixture with a magnetic stirrer. The foam stability is subsequently evaluated in terms of its height change as a function of time. It is found that the increasing surfactant concentration contributes to an increase in foam stability; foam stability is insensitive to surfactant concentration when the surfactant concentration is above the threshold CMC. As for the C3H8 foam, an elevated temperature is detrimental to foam stability. At a higher temperature, the effective critical micelle concentration (CMC) of surfactant also increases. In general, the stability of C3H8 foam is negatively affected by an increasing salinity. As n-C16H34 is added to the solution, foam stability deteriorates. In order to study the effect of solvent type on foam stability, CO2 is used to replace C3H8 for generating foam, with the consideration of different salinity and temperature conditions. In comparison, CO2 foam only exhibits several minutes of half-life at any conditions, which is much shorter than the C3H8 foam. Additional flow experiments are also conducted by alternately injecting C3H8 and Triton X-100 solution into a glass beadpack. The pressure difference during the experiments is recorded so as to obtain the mobility of the dynamic flow in the porous media. It is found that alternating C3H8 and Triton X-100 solution results in a larger pressure difference, hence leading to more mobility reduction than alternating C3H8 and water through the porous media. (C) 2016 Elsevier B.V. All rights reserved.