Effects of the Non-ionic Surfactant (CiPOj) on the Interfacial Tension Behavior between CO2 and Crude Oil

The interfacial tension (IFT) between CO2 and crude oil is considered as one of the key properties for the CO2 flooding process, and a reduction in IFT is desirable to improve the efficiency of the process. In this work, propoxylated surfactants denoted as CiPOj (where Ci is the hydrocarbon tail and POj are oxypropylene groups, with i = 12 and j = 4–9) were adopted to reduce the IFT between CO2 and crude oil by means of the pendant drop method. The results reveal that the IFT was significantly reduced or even close to zero and the miscible phenomenon was observed in the presence of CiPOj. In comparison to pentane or ethanol, CiPOj at a dosage of 0.5 wt % causes far higher reduction of the IFT than 20 wt % pentane or 5 wt % ethanol. With the increase of the CiPOj dosage, the IFT was reduced and the slope of IFT versus pressure was increased. However, there is a threshold dosage; further addition of CiPOj beyond the threshold could no longer reduce the IFT. Moreover, attributed to the amphiphilic characteristic of CiPOj, the minimum miscibility pressure (MMP) and the first-contact miscibility pressures (Pmax) of the crude oil/CO2 systems were decreased from 19.1 and 43.0 to 13.8 and 19.0 MPa at CiPOj dosage of 0.6 wt % and temperature of 333 K, respectively.