CO2-Based Fracturing Fluid: Evaluation of a Novel Foaming Agent Under High Temperature and Salinity Conditions

Hydraulic fracturing in unconventional reservoirs has traditionally relied on water-based fluids, but this approach suffers from excessive water consumption and environmental challenges. CO2 foam fracturing fluids have emerged as a promising alternative, offering up to an 80% reduction in freshwater usage while improving proppant transport and formation cleanup. Therefore, this study develops a surfactant-stabilized CO2 foam system using seawater as the base fluid, aming to achieve high viscosity and stability of CO2 under high-pressure, high-temperature (HPHT) conditions. The study evaluated foam rheology with a customed HPHT foam rheometer at 150 °C and 1,000 psi to assess the durability of foam's viscosity, which indicates its stability. Novel surfactant formulation was tested with and without the addition of a gel stabilizer or a high-temperature (HT) stabilizer. The CO2 foam with the gel stabilizer achieved an initial viscosity of up to 55 cP at 100 /s shear rate, which was reduced by about 9% after 30 minutes and nearly18% after 60 minutes at 150 °C. These results indicate significant improvement of the thermal stability compared to the surfactant-only foam (which dropped to 35 cP in 60 minutes). The optimized foam also demonstrated compatibility with high-salinity brine and maintained viscosity at shear rates up to 1000 /s, suggesting effective proppant suspension capability. By using low concentrations (0.5 and 1 wt%) of surfactant and readily available stabilizers, the formulation minimizes chemical loading. This work confirms the viability of a seawater-based CO2 foam fracturing fluid that substantially reduces water usage while achieving the viscosity requirements for proppant transport in ultralow-permeability reservoirs. The findings provide a foundation for an environmentally sustainable and cost-effective foam fracturing technique to substitute the excessive use of fresh water in hydraulic fracturing.