To construct the in-situ emulsification and viscosification system that is suitable for low permeability oil reservoirs characterized by high-temperature and high-salt, the amphiphilic Janus SiO₂ nanoparticles and Tween 60/Imidazoline oleate surfactant system were combined. The mechanism of in-situ emulsification and viscosification system was elucidated from two aspects: The dynamic adsorption and phase conversion of surfactant, and the unique bridge structure of Janus nanoparticle stabilized emulsion. The successful synthesis of Janus SiO₂ nanoparticles with varying degrees of hydrophilicity and hydrophobicity was achieved through regulating the reaction conditions. Based on emulsion stability, the optimization of the modification degree of Janus SiO₂ nanoparticles was achieved. The in-situ emulsification and viscosification system was constructed by introducing Tween 60/Imidazoline oleate as dispersion aid agent and emulsifier. Notably, the in-situ emulsification and viscosification system can be stably dispersed for more than 12 hours in high-temperature and high-salt. The dispersion stability of the in-situ emulsification and viscosification system was evaluated qualitatively by visual inspection, Turbiscan stability index and monitoring particle size. The emulsification ability, emulsion stability and rheological properties of the systems with different concentrations were evaluated at 90 ℃ and a salinity of 35,000 ppm. It was found that the in-situ emulsification and viscosification system with the concentration of 0.64 wt% shows better profile control and enhanced recovery performance. This study presents a new approach for profile control using amphiphilic Janus nanoparticles and provides a promising prospect for applying nanoparticles in the field of enhanced oil recovery.

Inadequate strength and stability of active crude oil emulsions stabilized by conventional surfactants always lead to a limited plugging rate of plugging agents. Thus, to address this issue, the synthesis of amphiphilic Janus nanosheets was effectively carried out for enhancing the system performances and subsequently characterized. Based on the outcomes of orthogonal tests, an assessment was conducted on the nanosheet and surfactant formulations to optimize the enhancement of emulsion properties. The experimental demonstration of the complex system has revealed its remarkable emulsifying capability, ability to decrease interfacial tension and improve rheological behavior at high temperature (80 ℃) and high salinity (35,000 ppm) conditions. Involving probable mechanism of the system performance enhancement is elucidated by considering the synergistic effect between surfactants and nanosheets. Furthermore, variables including water-to-oil ratio, salinity, temperature and stirring intensity during operation, which affect the properties of prepared emulsions, were investigated in detail. The efficacy and stability of the complex system in obstructing medium and high permeability cores were demonstrated. Notably, the core with a high permeability of 913.58 mD exhibited a plugging rate of 98.55%. This study establishes the foundations of medium and high permeability reservoirs plugging with novel active crude oil plugging agents in severe environments.

Nanotechnology has been increasingly applied in the petroleum industry in recent years. In particular, dispersions consisting of nanoparticles and surfactants have been widely investigated. The imbibition system compounded by nanoparticle and surfactant was found to display a high efficiency in enhancing oil recovery. This paper briefly reviews the factors influencing imbibition efficiency. At the same time, the application and mechanism of the imbibition system of nanoparticle-surfactant dispersion in the field of enhanced oil recovery are introduced. Additionally, the limitations and challenges that the imbibition system of nanoparticle-surfactant dispersions may face in enhanced oil recovery applications are put forward. The current work reveals that the imbibition system with nanoparticle-surfactant dispersion is an ideal candidate for enhanced oil recovery in tight and low-permeability reservoirs.