Mobility Control using Nanoparticle-Stabilized CO2 Foam as a Hydraulic Fracturing Fluid

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Abstract CO2-foam has been used as a fracturing fluid to develop unconventional resources and specifically for water-sensitive reservoirs. CO2-foam not only reduces formation damage by minimizing the quantity of aqueous fluid which enters the formation, but also reduces the water consumption for environmental conservation purposes. CO2-foam as a hydraulic fracturing fluid provides for rapid cleanup during flowback. Although it is common to use surfactants to generate and stabilize foams, they tend to degrade at high temperatures (>212°F) and in high-salinity environments. The present work evaluates new foaming solutions that incorporate nanoparticles to investigate the mobility-control performance when such foams are used as hydraulic fracturing fluids. Of special interest in this work is the study of mobility reduction factor (MRF) of CO2 foam, generated with polymer-based solution, e.g., guar gum, in the presence and absence of nanoparticles, to assess the apparent fluid viscosity at high temperature and high salinity. To achieve this objective, coreflood tests were conducted on different Buff Berea sandstone cores at both 77 and 250°F. CO2 gas was injected with the different solutions simultaneously to generate foam with 80% quality. The pressure drop across the core was then measured to estimate the MRF. Results show that alpha olefin sulfonate (AOS) improves the MRF by 300% compared to NaCl solution. Adding silica nanoparticles and guar-gum to the AOS solution improves both foam stability and MRF. At 250°F, the AOS solution retained foam stability, while the MRF increased to 28 compared to that of at 77°F. Choice of surfactant concentration is a critical parameter in generating stable foam. However, the economical use of surfactants is limited by various factors such as surface adsorption, process cost, surfactant loss, and surfactant degradation at high-temperature reservoirs. Nanoparticle solutions can be employed to improve CO2 foam stability as well as MRF factor. Adding nanoparticles is highly recommended for hydraulic fracturing applications, particularly in fracturing stimulation at high-temperatures.