A novel concept of treating oil reservoirs by nanofluids is being developed to improve oil recovery and reduce the trapped oil in hydrocarbon reservoirs. Nanoparticles show great potential in enhancing oil recovery under ambient conditions. In this paper, the approaches of wettability alteration by using nanofluid, stability of nanofluids, and the most reliable wettability alteration mechanisms associated with variant types of nanoparticles have been reviewed. Moreover, the parameters that have a significant influence on nanofluid flooding have been discussed. Finally, the recent studies of the effect of nanoparticles on wettability alteration have been summarised and analysed. Furthermore, this paper presents possible opportunities and challenges regarding wettability alteration using nanofluids.

Herein, the pressure decay method was improved to obtain the CO ₂ diffusion coefficient in fractured-vuggy carbonate reservoirs at 393 K and 50 MPa and obtained good correlation results between bulk and porous media by porosity and tortuosity.

Recently, much attention has been directed toward nanofluids’ applications for enhanced oil recovery (EOR). Here, amphiphilic molybdenum disulfide (KH550-MoS₂) nanosheets are synthesized using a hydrothermal approach. The physicochemical properties and EOR potential of ultralow concentration KH550-MoS₂ nanofluids are systematically investigated at Changqing Oilfield (China) reservoir conditions (temperature∼55 °C and salinity∼7.8 × 10⁴ mg/L). Interfacial tension (IFT), wettability alteration and emulsion stability are characterized to evaluate the physicochemical properties of KH550-MoS₂ nanofluids. The results show that ultralow concentration KH550-MoS₂ nanofluid (50 mg/L) can decrease IFT to 2.6 mN/m, change contact angle (CTA) from 131.2° to 51.7° and significantly enhance emulsion stability. Core flooding experiments are conducted to determine the dynamic adsorption loss law and oil displacement efficiency of KH550-MoS₂ nanofluid. Results indicate that the cumulative produced KH550-MoS₂ nanosheets ratio to total injected KH550-MoS₂ nanosheets (CNR) reaches 91.5% during flooding in a low permeability reservoir. Moreover, ultralow concentration KH550-MoS₂ nanofluid can increase oil displacement efficiency by 14% after water driven. This work offers a new amphiphilic nanofluid with high efficiency for EOR. Graphical Abstract

In-situ emulsification and viscosification system of surfactant-assisted Janus nanofluid and its profile control effect