Jitendra Sangwai

Hypothesis: Low salinity surfactant nanofluids have recently shown promising characteristics in wettability alteration of the silicate-based rock representative substrate and interfacial tension reduction of oil/aqueous phase interface. Pore level understanding of the physical processes entailed in this new class of low salinity injection fluids in oil-phase saturated real rock porous media is required, which has not been conceived yet. Experiments: Thus, we investigate the oil recovery performance and possible mechanisms of oil recovery by the injection of low salinity surfactant (SDBS, 1.435 mM) aqueous solutions (with 0%, 0.01% and 0.1% (by weight) ZrO2 nanoparticles) into the oil phase saturated Doddington sandstone miniature core plugs. The designed experiment involves core flooding with X-ray transparent core-holder developed in-house and analysis/processing of the acquired image data. Findings: The injection of low salinity surfactant nanofluids with 0.01% ZrO2 nanoparticles leads to maximum oil phase recovery. The results suggest that the dominating mechanisms for oil recovery are wettability alteration, inherent interfacial tension reduction, and the effect of significant amount of microemulsions formation is rather trivial. Low salinity effect, even in combination with surfactant, caused fines migrations (not reported earlier), is found to be significantly mitigated using nanoparticles. This new class of fluids may significantly enhance oil recovery.

Advanced low-salinity aqueous formulations have shown promising results for rock wettability modification and interfacial tension reduction. Additives, such as surfactant and nanoparticles, can be used for such formulations. The interaction of these novel formulations with different fluid phases and the rock surface is, however, yet to be understood in detail. Thus, an experimental study was conducted in this study to investigate the interfacial tension and wettability of carbon dioxide and anionic surfactant (SDBS, 1.435 mM) at high pressure and temperature. The results show that the anionic surfactant (SDBS, 1.435 mM) augmented the effect of zirconia (ZrO2) nanoparticles (100-2000 mg/L concentration) at low-salinity conditions and proved to be an effective wettability and interfacial tension modifier when used at appropriate divalent cation/sulfate ion ratios. Low-salinity surfactant nanofluids may thus be applied for wettability alteration and interfacial tension reduction for recovering residual oil, carbon dioxide-enhanced oil recovery, as well as carbon dioxide geosequestration. We also demonstrate in this study that the ratio of divalent cations to sulfate ions (0 ≤ M2+/SO42-≤ 4.427) has a significant role in interfacial tension reduction and wettability modification. We further show using contact angle wettability measurements that initial weak water-wet quartz surfaces can turn to more water-wet when zirconia nanoparticles used in the low-salinity formulation are in the range of 100-1000 mg/L. Interestingly, further incremental nanoparticle concentration decreases the water wettability but further reduces the carbon dioxide/brine interfacial tension.