Polyelectrolyte Complex Stabilized Supercritical CO2 Foam Systems Used for Hydraulic Fracturing Applications

Abstract

The objective of this research is to develop polyelectrolyte complex nanoparticles capable of stabilizing surfactant-generated supercritical CO2 foam systems prepared for hydraulic fracturing applications. The polyelectrolyte pH, polycation/polyanion ratios and surfactant/PECNP ratios were optimized in order to generate stable polyelectrolyte complex nanoparticles by maximizing the absolute zeta potential of the resulting nanoparticle. Next, high pressure, high temperature rheometer tests were conducted to study the bulk rheology of foam systems of varying surfactant/PECNP ratios for different foam qualities. The effect of shear, foam quality and presence of PECNP on the rheology of the foam was understood. Surfactant-PECNP generated scCO2 foam showed better rheological properties than surfactant generated scCO2 foam. The viscosity of the foam system increased with increase in foam quality. The same scCO2 foam systems used in rheology experiments were tested for durability and stability in a view cell experiment both in the presence and the absence of crude oil. The foam lamellae were stabilized due to reduced dynamic movement of surfactant micelles caused by electrostatic interactions with PECNPs, this imparted high durability and stability to scCO2 foam. The PECNP-surfactant generated foam proved to be more stable and durable compared to surfactant generated scCO2 foam and foam stability increased with increase in foam quality. Supercritical CO2 foam systems showed less durability in view cell test with crude oil, due to quick drainage of foam in presence of crude oil, which is favorable for improving the post fracture cleanup efficiency. Based on the rheology and view cell test, the most optimized surfactant-PECNP ratio was found. Further, this ratio of surfactant-PECNP was used to generate scCO2 foam for dynamic fluid loss and clean up experiments. Dynamic fluid loss experiments were performed in the high pressure, high temperature foam setup. Supercritical CO2 foam generated by surfactant had low fluid loss, thus low fluid loss coefficient. The fluid loss was even further reduced in case of scCO2 foam generated by optimal surfactant/PECNP ratio. Sand pack tests using crude oil from the Mississippian limestone play were performed to understand the post-fracture cleanup of CO2 foam. Surfactant-generated scCO2 foam showed promising cleanup efficiency. However, further increase in cleanup efficiency was observed by using the most optimal surfactant-PECNP generated scCO2 foam. Through this research, an optimal surfactant-PENCP generated scCO2 foam system was developed for fluid loss control, rheological measurements, and to improve post fracture cleanup in hydraulic fracturing.