The synergistic role of silica nanoparticle and anionic surfactant on the static and dynamic CO2 foam stability for enhanced heavy oil recovery: An experimental study

CO2 foam is a promising candidate in enhanced oil recovery and reducing anthropogenic CO2 emission through geo-sequestration due to its CO2 mobility control ability. However, instability of CO2 foam stabilized solely by surfactant strongly retards its application. Here, two types of silica nanoparticles (NPs) with varied hydrophobicity are used with sodium bis(2-ethylhexyl) sulfosuccinate (AOT) to increase CO2 foam stability. Through foamability and foam stability experiments, together with complementary experiments such as measurements of CO2-water interfacial tensions, particle zeta potential, and adsorption isotherm of surfactant, the stabilization mechanisms of AOT-NPs aqueous dispersions on the CO2 foam films are revealed. Oil recovery experiments are performed in an oil-wet micromodel where high permeability channels are included to mimic wormholes in unconsolidated sandstone reservoirs during sand production. Results show that the nanoparticle surface hydrophobicity strongly influences the interactions between particles and AOT. Partially hydrophobic NPs (NPB) are much more efficient in generating and stabilizing CO2 foam than hydrophilic NPs (NPA) when mixed with AOT in a proportion of 1: 0.16 (wt%/wt%). AOT-NPB dispersions improve the recovery in two aspects: First, the synergistic interactions between AOT and NPB leads to the adsorption of AOT on particle surfaces, thus enhancing mechanical strength of bubbles. High quality foam encompasses a fine foam texture and provides higher resistance to the gas flow, leading to a more uniform sweep. Second, AOT-NPB dispersions reduces oil/water IFT, promotes emulsification forming oil in water (O/W) emulsions, and alters glass surface wettability, leading to substantial incremental oil recovery.