Achieving solubility alteration with functionalized polydimethylsiloxane for improving the viscosity of supercritical CO2 fracturing fluids

Abstract

Supercritical carbon dioxide (SC-CO₂) fracturing technology has the characteristics of a large amount of fixed CO₂ and anhydrous fracturing. It has great application potential for developing unconventional oil and gas resources and mitigating the greenhouse effect. However, the low viscosity of SC-CO₂ limits the development of this technology. In this work, HS series thickeners were prepared via a ring-opening polymerization and hydrosilylation reaction by a molecular simulation-aided design method. The simulation results of cohesive energy density, interaction energy, and radial distribution function are consistent with the visualization experimental results, which proves that HS (hyperbranched siloxane) series thickeners have excellent solubility in SC-CO₂. HS-3 is the best thickener in the HS series. At 305.15 K and 10 MPa, 5 wt% HS-3 (60 s⁻¹) increases the viscosity of SC-CO₂ by 151 times, and the apparent viscosity is 3.024 mPa s. The apparent viscosity of SC-CO₂ was positively correlated with the pressure and concentration but negatively correlated with the temperature and shear rate. The results indicate that it is feasible to introduce an aliphatic group and polysiloxane into a SC-CO₂ thickener by hydrosilylation.