Sub-millimetric visualization and stability measurement for supercritical CO2 foams: Effect of ionic complexation on tubular and diverging flows

Development of natural gas resources as fuel for energy transition requires sustainable recovery processes with manageable amount of water used for unconventional stimulation of wellbores to protect the environment. To manage stability issues and bubble morphological alternations within the waterless fluids such as dry foams, microstructure and physiochemical properties were correlated to ionic complexation, bubble local plastic deformation (T1 event) in vicinity of constriction and elastoplastic behavior of CO2-water interface travelling from wellbore to fracture and flow back. This work presents facile sub-millimetric observation and step by step image analysis protocol for dry scCO2 foam transport and stability evaluation across the vertical view cell (tubular flow) and after constriction (diverging flow) and highlights the effect of viscoelastic components of interface on bubble plastic deformation and interfacial stability. The scCO2 foam’s microscopic structure was stabilized with (i) Zwitterionic Surfactants (ZS) and (ii) ZS-conjugated Polyelectrolyte Complex Nanoparticles (PECNP). PECNP-Surfactant scCO2 foam structure was noticeably affected by confinement ratio between the feeding tube and view cell, thus excessive lamella breakup and rearrangement of scCO2 bubbles occurred with higher rate in widening flow, which contributed to formation of less uniform dispersion of scCO2 droplets in PECNP-Surfactant scCO2 foam. However, the PECNP-Surfactant complexes residing in CO2-water lamella stabilized the deformed microstructure for significantly longer time. Bubble shape deformity was attributed to bubble elongation due to elastoplastic properties of lamella interface originated by the presence PECNP nanoparticle verified by higher dilatational elasticity at interface. Stability of deformed bubbles in pattern of PECNP-surfactant scCO2 foam with longer resistivity to lamella breakage, coalescence, and gravity drainage (up to 160 min) were compared to sudden bubble growth and expansion (after 30 min) detected for narrower distribution of smaller scCO2 bubbles stabilized in mixtures of ZS in high salinity brine (33.3 kppm). Higher resistance to morphological change (coalescence, rupture, burst) was observed for viscous lamella of PECNP-surfactant in scCO2 foam originated from higher viscosity and dilatational elasticity of lamella interface.