Probing the Effect of Wettability on Transport Behavior of Foam for Enhanced Oil Recovery in a Carbonate Reservoir

Foam for enhanced oil recovery in carbonate reservoirs is generally challenging because the oil-wet formation is not favorable for generating and stabilizing the lamellae. With an alkyl-polyglucoside surfactant, a series of foam core flooding experiments both in the absence and in the presence of crude oil were performed on Estaillades limestone, a dual porosity and heterogeneous carbonate presenting reasonable similarities with the reservoir formation. The effects of wettability, surfactant concentration, and foam quality on foam strength were systematically investigated. It is found that the foam strength in the presence of oil is generally smaller than that in the absence of oil, and the foam strength in the oil-wet condition is typically lower than that in the water-wet condition. However, for the water-wet condition, the foam strength can be greatly improved by increasing the surfactant concentration, which is getting closer to that in the absence of crude oil at a sufficiently high surfactant concentration. The combined effect of a high remaining oil saturation and the disadvantageous wettability can further destabilize foam, thereby greatly reducing the foam strength at oil-wet conditions. As a result, the foam flooding under the water-wet condition outperforms that at the oil-wet condition. Furthermore, it is found that the foam behavior at a high gas fraction is more sensitive to the wettability of rock and the foam hysteresis effect.