The influence and mechanism of alkyl block polyethers on the interfacial tension and minimum miscibility pressure of CO2 and shale oil

The successful application of CO2 in developing shale oil can increase oil production and reduce CO2 emission. Reducing IFT and facilitating miscibility between CO2 and oil is the critical mechanism for enhancing shale oil recovery by CO2 flooding. Here, the effects of alkyl block polyethers on the interfacial tension and minimum miscibility pressure of CO2 and shale oil has been investigated by experiments and the influence mechanism of polyether on IFT and MMP has been explored by molecular dynamic simulations. The experimental results show that among the three polyethers, C4(PO)6 has the best effect to decrease the IFT and MMP of CO2 and shale oil. The IFT and MMP decrease with the increasing concentration of C4(PO)6 in CO2. The IFT and MMP can be decreased to a lower value when the polyether is dissolved in CO2 than in oil phase. The molecular dynamic simulations show that polyether molecules can diffuse from CO2 phase to the interface of CO2 and oil to decrease the IFT and further diffuse to oil phase to accelerate the miscibility process of CO2 and oil. The presence of polyether molecules can decrease the interaction energy, especially the vdW interactions between CO2 and oil molecules to decrease the IFT and MMP. The reduction of interaction energy is due to the dispersion force and LA-LB interactions between polyether and CO2, as well as the dispersion force interactions between polyether and oil molecules. The finding is significant to the chemical design for decreasing the IFT and MMP of CO2 and oil and further to successfully and efficiently develop shale oil by the CO2-surfactant mixed fluid.