Application and Mechanisms of Self-Generated Heat Foam for Enhanced Oil Recovery

Foams are widely used in the oil and gas industry due to their unique viscous and elastic properties. However, typical foam injection methods into reservoirs require large equipment with high injection pressure, which might not be suitable for development of offshore oilfields, deep wells, or high condensate petroleum reservoirs. Here, for the first time, we report self-generated heat foams (SGHFs) that are systematically generated and studied by combining self-generated nitrogen gas reactants (sodium nitrite and ammonium chloride) and environmentally friendly surfactants. Sandpack oil recovery flooding experiments at 60 °C and 4 MPa along with two-dimensional (2D) visualization micromodel experiments were carried out to analyze the oil displacement mechanisms. Various oil recovery aspects such as heat production, oil viscosity reduction, foam generation, profile control, and heat-foam synergistic effects were investigated. The results showed that SGHFs can increase oil recovery by 33.9% from homogeneous (permeability of ∼2 Darcy) single layer formation and by 20.4% from heterogeneous (permeability ratio >10) multilayer formation. The incremental oil recovery by SGHFs was much higher than that of conventional foam or self-generated heat (SGH) without foam. The heat produced by the SGHF chemical reaction increased the temperature of the crude oil by 13 °C, reduced the crude oil viscosity by 35%, and helped increase oil recovery by reducing the mobility ratio. Moreover, the foams generated by SGHFs had a remarkable effect on the profile (conformance) control in the presence of crude oil. The synergistic effect between the heat and the foam produced by SGHF chemical reaction can be explained by (1) The chemical reaction can produce small and uniform foam, seen by the 2D micromodel, which can block large pores in porous media and enhance sweep efficiency and (2) The uniform sweep efficiency due to the presence of foam can help distribute the heat and make the temperature rise evenly along the sandpack, which was beneficial to reduce the crude oil viscosity throughout the entire porous media and improve oil recovery.