Analysis on the mechanism and characteristics of nanofluid imbibition in low permeability sandstone core pore surface: Application in reservoir development engineering

In this work, the mechanism of nanofluid imbibition in the development of low permeability reservoirs is studied. Firstly, by analyzing nuclear magnetic resonance (NMR) curves and imaging maps, the imbibition displacement effects of low-permeability reservoirs in water and different nanofluids are compared. Subsequently, the influ-ence characteristics of rock modification mechanism of nanofluid on imbibition displacement are analyzed by three-phase contact angle experiments. Finally, the attraction forces between oil and rock surfaces with different properties are measured by atomic force microscopy (AFM) experiments, and the influence of wetting inversion of nanofluids on the adsorption between oil and reservoir rocks is evaluated. The results show that the relaxation time map area of the core treated with nanofluid is smaller than that of the core treated with water, and the NMR images show that the nanofluid has a higher sweep efficiency, indicating that nanofluid can improve the oil displacement efficiency of low-permeability reservoirs. The higher the nanoparticle concentration of fluid, the more significant the effect. In addition, the effect of nanofluids on oil displacement efficiency in small pores and large pores of the reservoir is obvious, and the increase amplitude is 30 % and 50 %, respectively. Scanning electron microscope (SEM) images show that nanoparticles adsorbed on the reservoir inner wall exert a wetting inversion effect, leading to changes in reservoir wettability and promoting imbibition oil displacement, which is also reflected in the NMR maps. Contact angle experiments show that nanofluids convert the lipophilicity of rock surface into hydrophilicity, and the contact area between oil and rock shrinks due to the change of wettability and the decrease of interface energy, which weakens the adsorption between the two, promotes capillary imbibition of fluid and oil displacement. The AFM experiment confirms that nanoparticles reduce the micro-scopic adsorption force between oil and rock through wetting inversion and interface energy reduction. It is less difficult for the fluid to peel oil from the reservoir rock, which promotes the oil displacement. The studies show that nanofluid imbibition has advantages in the field of low permeability reservoir development.