Nanoscale flow model modelling and analysis of tight reservoir based on viscosity change and interfacial slip characteristics in confined space

Abstract

Understanding the flow mechanisms between hydrocarbons and interfaces in nanopores is critical for fluid supply in tight reservoirs with huge reserves. In this paper, the nanoscale liquid-solid interface interaction potential is analyzed based on the molecular interface theory, and a new nanoscale fluid viscosity model is constructed through the Eyring model, and the fluid velocity and flow flux models in nanopores are derived based on the liquid-solid interface slip condition. In addition, n-pentane flow characteristics in quartz nanopores were investigated with key parameters including: the Hamaker constant, the decay length, the wetting angle, the boundary slip and the flux coefficient. The proposed model is validated in a comparison of theory, simulation and laboratory results. The study results show: (1) influenced by the liquid-solid interfacial effect, there is a viscosity gap between the fluid in the bulk and at the boundary, resulting in a non-linear variation of the flow velocity. Of the multiple microscopic forces considered by the model, Ligshitz-Van der Waals force has the strongest effect in confined pores below 40 nm, and electrostatic force has the weakest effect. When the pore diameter less than 10 nm, the constrained fluid viscosity was improved above 4 times. (2) based on the microscopic liquid-solid interface slip condition, a constrained space velocity model is derived, which indicates that the flow is directly dependent on the effective shear stresses on the fluid and the strength of the liquid-solid interface effect. Under the low shear stress in a tight reservoir, the slip at the liquid-solid interface has obvious linear characteristics, and the slip velocity depends on the effective shear stress. The liquid-solid interfacial effect parameter is increased from 1 to 30, and the slip velocity is reduced to 3.2 Å/ps, which is a 55% reduction. (3) in this paper, the hamaker constant of n-pentane-quartz interface based on the molecular spacing variation and the decay constant for different water types and solute concentrations are obtained, and the effect of the decay length on the flow coefficient of the nano confined flow model is explored for different pore radiuses. The flux coefficient increases with pore radius, and the effect of the decay length is greater for pores <100 nm.