CO2 Mobility Control in Porous Media by Using Armored Bubbles with Silica Nanoparticles

CO2 mobility control in porous media is crucial to geological sequestration of CO2 and enhanced oil recovery (EOR). Although aqueous foam has been widely used to control the mobility of CO2, bubble dispersion with low gas content is formed easily because of gas-liquid separation caused by gravity differentiation, which reduces the storage volume of CO2 and limits its utilization. In this work, the use of armored bubbles with silica nanoparticles for CO2 mobility control in porous media was explored. Visual micromodel flooding experiments were conducted to study the pore-scale flow behaviors of bubbles. Both homogeneous and heterogeneous flooding experiments were used to evaluate the mobility control ability of bubble dispersions. The results showed that the nanoparticles were adsorbed on the interface of CO2 bubbles and formed an armor layer, which made the interface more solid-like and enhanced the roughness of the bubble film. Subsequently, the effective viscosity of the armored CO2 bubble dispersions increased and showed a shear-thinning property. By observing the pore-scale flow behaviors, it was found that armored bubbles showed high rigidity and strong plugging ability, thereby trapping CO2 in porous media and enlarging the sweep region. A synergistic plugging effect occurred between the armored bubbles, which drove the subsequent bubbles to invade into the residual oil region. Moreover, as the armored bubbles became rough, the residual oil was activated more easily by the scraping effect, and the oil-transporting ability of bubbles was enhanced. Thus, residual oils formed after water flooding could be displaced by armored bubbles thoroughly. In homogeneous porous media, the breakthrough and flow channels of the displacing fluid were controlled by the strong plugging of armored bubbles in porous media, and the displacement efficiency was enhanced. The ultimate oil recovery of armored bubble flooding was improved by about 11.4% compared to that of bare surfactant bubble flooding. In heterogeneous porous media, the mobility of the displacing fluid in relatively high permeability sand-pack was reduced more effectively by armored bubbles. Even during the subsequent water flooding stage, the armored bubbles showed relatively strong resistance to water erosion and inhibited the differentiation of outflow percentage. Therefore, the flow profile was controlled by armored bubbles, and the ultimate oil recovery was improved by about 14.3% using armored bubbles. The results confirmed the high mobility control performance of nanoparticle-armored bubbles for EOR.