An investigation of viscous oil displacement in a fractured porous medium using polymer-enhanced surfactant alternating foam flooding

Naturally fractured reservoirs are one of the hydrocarbon resources where the application of foam flooding is particularly recommended, as foam can divert the flow of displacing fluid from high-permeability regions (fracture networks) to low-permeability regions (rock matrix blocks). However, its application in heavy oil reservoirs is challenging and results in inadequate sweep efficiencies. The current practice of foam flooding (including polymer enhanced foam flooding, PEF) is inefficient in displacing high viscosity oils. This is due to large viscous forces associated with the oil phase flow and the high rate of bubbles coalescence (foam collapse), which make it difficult for foam to displace the heavy oil from the matrix. Thus, we investigated feasibility of polymer-enhanced surfactant alternating foam (PESAF) flooding (as a new hybrid enhanced oil recovery process) to displace the oil phase in porous media. We hypothesized that PESAF flooding can emulsify the oil phase and generate oil globules by reducing the interfacial tension forces between the oil and water phase, and also it increases the foam stability, leading to higher displacement efficiencies in the presence of viscous oils. For this purpose, three different oils (low, medium, and high viscosity oils) were used in a micromodel to simulate the immiscible displacement process in fractured rocks. The experimental results showed that PEF flooding is efficient in displacing the low viscosity oil, however it cannot yield a high efficiency displacement in viscous oil cases. It was found that the hybrid enhanced oil recovery (EOR) process of PESAF flooding can increase the oil recovery factors for the medium and high viscosity oil cases significantly. These experimental results supported the hypothesis of applying PESAF flooding to improve the displacement efficiency of high viscosity oils in fractured porous media.