CO₂ Viscosification by Poly-α-olefins: Effect of Pressure, Temperature, Concentration, and Monomer Chain Length

Direct CO2 thickening with low-molecular-weight oligomers may significantly broaden the use of CO2 in the subsurface and increase the efficiency and safety of subsurface sequestration. This study investigates the thickening of supercritical carbon dioxide (scCO2) using poly-α-olefins (PAOs). The research focuses on the effects of pressure, temperature, concentration, and monomer chain length on the solubility and viscosification of PAOs in scCO2. Our findings reveal that PAOs, particularly poly-1-decene of 20 repeat units (P1D-20) and a copolymer of 1-dodecene-1-hexadecene (Cop12/16-12), significantly increase the viscosity of scCO2 at low concentrations. P1D-20 increases the viscosity of CO2 six times at 1.5 wt % at 35 °C and 24 MPa. Cop12/16-12 thickens 75% more than P1D-20 at 0.3 wt %. The thickening limitation is its solubility. PAO’s thickening efficiency is not drastically affected by temperature; relative viscosity remains practically constant at temperatures above 100 °C. Oligomers with different branch lengths in the same molecule look promising for effective viscosification.