(706c) High-Pressure Solutions of C6F13- and C4F9- Based Polyfluoroacrylates in CO2: Solubility, Viscosity, Adsorption, and Sealing of Cement Cracks

Polyfluoroacrylates (PFAs) have drawn interest in recent decades due to their remarkable solubility in liquid and supercritical carbon dioxide. PFAs have been considered in many different applications in CO₂-related chemical engineering technologies and petroleum engineering projects (i.e. designing CO₂-soluble compounds and thickening CO₂ for more uniform flow of CO₂ through porous media during enhanced oil recovery). This project focuses on the use of CO₂-PFA solutions to improve wellbore integrity. Our initial attempts to seal small cracks in cement using CO₂-PFA solutions suggest that PFAs dissolved in CO₂ will strongly and adsorb onto cement surfaces. This deposition of a hydrophobic, oleophobic amorphous polymer dramatically changes wettability and reduces the gap size of the crack, both of which reducing crack permeability and – in some cases – completely sealing the crack. To better understand this crack-sealing process, we used a high pressure, high temperature, windowed, stirred, variable-volume cell to obtain PFA solubility in CO₂ and PFA-CO₂ solution viscosity for PFAs based on C6F13 and C4F9 pendant groups. We have also presented (for the first time, to the best of our knowledge) high pressure equilibrium polymer adsorption data for calcium carbonate particles immersed in liquid or supercritical solutions of CO₂ and PFA. By measuring changes in solid particle mass before and after 24 hours of immersion in PFA-CO₂ solutions of known initial PFA concentration, we determined the equilibrium amount of polymer adsorbed on solid particles of known surface area. The corresponding equilibrium concentration of PFA in CO₂ was calculated by material balance.