Laboratory Investigation of Liquid Injectivity in Surfactant-Alternating-Gas Foam Enhanced Oil Recovery
Time: 12:45 – 13:30, May 23
Surfactant-alternating-gas (SAG) is a favored method of foam injection, in part because of excellent gas injectivity. However, liquid injectivity is usually very poor in SAG. We report a core-flood study of liquid injectivity under conditions like those near an injection well in SAG application in the field: i.e., after a prolonged period of gas injection following foam. We inject foam (gas (nitrogen) and surfactant solution) into a 17-cm-long Berea core at temperature of 90°C with 40 bar back-pressure. Pressure differences are measured and supplemented with CT scans to relate water saturation to mobilities. Liquid injectivity directly following foam is very poor. During prolonged gas injection following foam, a collapsed-foam region forms near the inlet and slowly propagates downstream, in which water saturation decreases. This decline in liquid saturation reflects in part liquid evaporation, and also pressure-driven flow and capillary effects on the core scale. In the collapsed-foam region, subsequent liquid mobility is much greater than downstream, and liquid sweeps the entire core cross-section rather than a single finger. Mobility in the region of liquid fingering is insensitive to the quality of foam injected before gas and the duration of the period of gas injection. We find that there is a small region very near the well, crucial to injectivity, substantially different from that further out, and not described by current foam models. The results can inform a model for liquid injectivity based on radial propagation of the various banks seen in the experiments.