Effect of gas type on liquid injectivity in a surfactant-alternating-gas foam process

Foam is injected into geological formations in a number of applications, including enhanced oil recovery, CO2 sequestration, and soil remediation. Surfactant-Alternating-Gas (SAG) is one of the most common methods of foam injection. Injectivity is a key factor in a SAG foam process for both economics and diversion. Depending on process goals and local availability, varies types of gas can be injected. Previous studies suggest that gas properties play an important role in the evolution of gas and liquid injectivity in a SAG process. However, the mechanisms of the effect of gas type on injectivity remain poorly understood. In this study, various types of gas, N2, CO2 and Kr, are employed to investigate the effect of gas type on fluid behavior and injectivity in a SAG process. In one experiment, we partially pre-saturate injected liquid with CO2 to explore the effect of gas-dissolution capacity on liquid injectivity. We observe that the process of dissolution of trapped gas into liquid fingers is strongly affected by gas solubility. The lower the gas solubility in water, the slower the gas dissolution process, and the slower the rise in liquid injectivity. The gas-dissolution process takes much longer with injection of partially pre-saturated liquid than with unsaturated liquid. The propagation of the collapsed-foam front during gas injection is also affected by the gas type: the greater the solubility of water in gas, the faster the foam-collapse process. One practical implication is that CO2 SAG foam injectivity is substantially better than foam made with other gases. The data sets include: cross-sectional water saturation profile during liquid injection following Nitrogen foam obtained from CT scan. Foam scan data for various types of gas at the same superficial velocity. The sectional pressure gradient data during gas injection following foam, liquid injection following foam and a period of gas injection. Researchers can directly draw the curve of pressure gradient change against pore volumes liquid/gas injection in various scenarios.