Whereas surfactants have been utilized to stabilize CO2-in-water (C/W) foams, only recently have they been combined with nanoparticle amphiphiles to offer improved foam viscosity and stability. Highly viscous C/W foams are of interest in a variety of applications including enhanced oil recovery (EOR) and hydraulic fracturing. In this work, nanoparticles were added to surfactants to increase the foam stability, given the essentially irreversible adsorption of the nanoparticles at the CO2-water interface. The role of nanoparticles and surfactants in formation and stabilization of viscous foams was investigated in a porous beadpack using a mixture of surface-modified silica nanoparticles with zwitterionic or anionic surfactants. Surfactant structure and formulation variables including temperature, pressure, and salinity were varied to quantify their effect on foam properties. Interfacial properties were measured to design and interpret foam formation and stabilization mechanisms. In some cases, strong synergy was observed where the mixture of nanoparticles and surfactant produced significantly more viscous and stable foams than either nanoparticles or surfactant alone. CO2-in-water foams with viscosities of over 100 cP in a 1.2 darcy beadpack were generated, more than double the values when only surfactant was present. The nanoparticles alone stabilized weak or no foam. The surfactant lowers the CO2/water interfacial tension to facilitate the formation of CO2-in-water foams composed of small CO2 bubbles (&lt;100 micron diameter), while the adsorption of nanoparticles at the oil/water interface enhances emulsion stability by providing a large barrier to droplet coalescence and contributing to the disjoining pressure to slow film drainage. Weak interactions between silica nanoparticles and surfactant minimizes competition for surfactant molecules by nanoparticle surfaces and the CO2/water interface.

Carbon dioxide-in-water foams stabilized with interfacially active nanoparticles and surfactants

249th National Meeting (2015)

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