The comparison of interface properties on crude oil-water and rheological behavior of four polymeric nanofluids (nano-SiO2, nano-CaO, GO and CNT) in carbonates for enhanced oil recovery

Nanoparticles (NPs) are currently being used in different areas of petroleum exploration and production, such as drilling, well logging, reservoir management, and enhanced oil recovery (EOR). Nanofluids, prepared from NPs, have been used as a novel flooding for EOR due to the excellent performance in altering interfacial properties and improving rheological behaviors. The properties of nanofluids vary with the structure of nanofluids. Nonetheless, most of the previous studies have focused on a particular type of nanofluid, the interfacial properties of various polymeric nanofluids and their flow behaviors under harsh and challenging reservoir conditions have been rarely reported or compared in literature. In this study, four polymeric nanofluids, prepared by mixing nano-silica (nano-SiO2), nano-CaO, carboxyl functionalized graphene oxide (GO) and amino modified carbon nanotube (CNT) with partially hydrolyzed polyacrylamide (HPAM), were characterized through XRD, FT-IR, UV–Vis and SEM to confirm that the materials were successfully prepared. Then, the colloidal stability, interfacial tension (IFT) reduction, rheological behavior, and wettability on calcite surface of these polymeric nanofluids were also studied in comparison. The experimental results of CNT-NH2/HPAM nanofluid showed that the overlap degree of BS and ΔBS curves was high, oil/brine IFT reduced from 35.84 mN/m to 18.11 mN/m and the contact angle on calcite surface reduced from 139.69° to 47.985°, indicating that the nanofluids were colloidally stability, and both reduce the IFT and alter wettability effectively. Furthermore, the addition of SiO2 and CNT NPs enhanced the network structure significantly, and showed excellent rheological behavior of polymer solution with improved viscoelasticity. Finally, the CNT-NH2/HPAM nanofluid increased the additional oil recovery from 13.8% to 21.6% in core flooding experiments, with the oil displacement mechanism explained in detail. Therefore, the findings of this study can help for better understanding of the effect of NPs on polymeric nanofluids, and set the stage for future investigation into EOR application in carbonate reservoirs.