Rheology of Carbon Dioxide Foams Stabilized by Nanoparticles and Proppant Transpor

Foamed fluids with gas phase of carbon dioxide (CO2) have been applied as fracturing fluids to develop unconventional resources. It's essential to determine in-situ rheology of CO2 foams stabilized by nanoparticles in order to predict proppant transport in reservoir fractures and improve oil production.;This study determined the in-situ shear viscosity of supercritical CO 2 foams stabilized by nano-SiO2 in the Flow-loop apparatus at shear rates of 2975~17850 s-1 under reservoir conditions with the pressure of 1140+/-20 psig and 1550+/-20 psig and the temperature of 40°C (104 °F). Supercritical CO2 with the density of 0.25~0.67 g/ml (15.61~41.83 lbm/ft3) and the viscosity of 0.02~0.05 cp under typical reservoir conditions were applied to generate foams. The foams were tested with high foam quality up to 80% to minimize water usage and disposal. The effects of shear rates, salinity, surfactant, and nanoparticle sizes on the rheology of gas foams were experimentally investigated, and the optimal system is determined. Further, proppant transport by CO2 foams and the placement under static and dynamic conditions were numerically analyzed by considering non-Newtonian behaviors of CO2 foams.;The apparent viscosity of CO2 foams increased and foam formation was improved under high pressure. The numeric simulation demonstrated the buoyance force due to viscosity helps to offset the density gradient between proppant and proppant laden fluid, thus promote proppant to transport and create a better fracturing opening in reservoirs.