Foam has been employed as an Improved/Enhanced oil recovery (IOR/EOR) method to overcome gravity override and the channeling and fingering of the injected gas, which arises due to the low density and viscosity of the injected fluid combined with the rock heterogeneity. A major challenge; however, is the stability of the generated foam when it contacts the oil. Foam boosters, which are generally costly surfactants, have been co-injected together with the main foaming surfactant to create stable foams in the presence oil. Similar to surfactants, particles can also accumulate at the gas-liquid and liquid-liquid interfaces. The difference is that the energy of adsorption and desorption of particles to the interface is so large that their adsorption is considered irreversible. Nanoparticles are orders of magnitude smaller than pore throats and therefore can easily flow through porous media.

In this study we investigate the possibility of replacing the expensive foam boosters with inexpensive nanoparticles made of coal fly-ash, which is abundantly available as a by-product of coal power plants. We investigate the viability of reducing the size of fly-ash particles using high frequency ultrasonic grinding. We also study the foaminess (foamability) and stability of the foams made with minor concentrations of fly-ash nanoparticles and surfactant both in bulk and porous media. The effect of monovalent and divalent ion concentration on the foaminess of the nano-ash suspension combined with very low concentrations of a commercial alpha olefin sulfonate (AOS) surfactant, in presence and absence of oil, is studied.

We observe that bulk foam that contains very small amounts of nano-ash particles shows a higher stability in presence of model oils. Furthermore, experiments in porous media exhibit remarkably stronger foam with mixtures of nano-ash and surfactant, such that the amount of produced liquids from the cores significantly increases. In presence of oil, the nano-ash-AOS foam shows a higher stability, although crude oil tends to form stable emulsions in water in presence of nano-ash.

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