Effects of the surfactant and pressure on the supercritical CO2 displacement efficiency in the porous media of geological storage sites

Laboratory scale experiments were conducted to investigate quantitatively the effects of a non-ionic surfactant (Tween 80) and the pore pressure on the supercritical CO₂ (scCO₂) displacement efficiency in porous media under subsurface storage conditions. The scCO₂ displacement efficiency increased by up to 52 % with the addition of the surfactant to the water (1.0 wt%) at a pore pressure of 8 MPa. The interfacial tension between the water and the scCO₂ decreased by up to 59 % and the contact angle of the water increased to 23 % with the surfactant addition in the water (15 % increase of the capillary number: C_N). As the pressure increased from 8 MPa to 20 MPa, the interfacial tension decreased by 40 % but the scCO₂ viscosity increased by 60 %, resulting in an 18–28 % increment of the scCO₂ displacement efficiency (27 % and 38 % increase in C_N and V_R (viscosity ratio), respectively).