Lattice Boltzmann Simulation Of Tight Oil Flow Mechanism Based On Digital Core

Tight oil is a new hot spot for unconventional oil and gas exploration and development in the world.It has extremely high mining value,but it is very difficult to mine because the reservoir of tight oil has special characteristics and belongs to low-permeability reservoir with strong heterogeneity.Poor physical properties and complex pore structure.In order to improve the tight oil production and the recovery of tight oil,it is necessary to study the fluid flow mechanism in tight oil reservoir rocks,explain the influence of pore structure,fluid properties and other factors on fluid flow in tight oil reservoirs,and understand the macroscopic seepage law.In this paper,the lattice Boltzmann method is used to simulate the fluid flow in tight oil reservoirs,and the effects of pore structure and fluid properties on the flow of single-phase fluid and two-phase fluid are studied.The lattice Boltzmann method can describe the interaction between multi-component multi-phase fluids from a microscopic point of view.The processing of complex boundaries is much simpler than the traditional methods,and it is very advantageous for studying such problems.The CT digital scanning technology was used to establish the digital core of typical tight oil reservoir rocks.The microscopic pore structure parameters of the rock cores of 20 tight oil reservoirs were counted.The single digital flow simulation was carried out using these 20 digital cores.The influence of scale and pore throat shape on the flow of single-phase flow,and the nonlinear seepage in the core is analyzed to study the relationship between pore structure and nonlinear seepage.The Shan-Chen model using lattice Boltzmann method is used to conceptual model and two-dimensional numbers.The oil-water two-phase flooding in the core was simulated,and the effects of pore width,connectivity,pore shape,pressure gradient,two-phase viscosity ratio and density ratio on two-phase flooding were studied.In the single-phase flow simulation of tight oil reservoir rock,under the constant velocity injection condition,the smaller the average throat radius of the digital core,the larger the average flow velocity of the fluid,but the smaller the flow velocity increases as the average throat radius decreases.In the same pore throat,the fluid velocity in the middle part of the pore throat is large,and the fluid velocity near the wall surface is small;in different pore throats,the fluid flow velocity at the larger radius throat throat is smaller,and the fluid with smaller radius pore throat is smaller.The flow rate is large.In the study of nonlinear seepage in tight oil reservoir rocks,the nonlinear seepage mode associated with microscopic pore structure parameters is obtained.In the two-phase flow simulation,for the pore structure,increasing the pore width and pore connectivity can increase the displacement speed,but as the pore width and connectivity increase,the degree of displacement will also decrease.For pressure and fluid properties,increasing the pressure gradient and lowering the displacement phase viscosity can speed up the displacement,and can make the displacement phase break through some hard-todisplacement pores,increasing the displacement surface,but with the pressure gradient.The increase in the viscosity of the lift and the displacement phase will gradually decrease as the displacement speed increases.Reducing the density ratio of the two phases can speed up the displacement and increase the displacement efficiency.In actual production,the speed of oil recovery can be accelerated by reducing the viscosity of the displacement phase,increasing the pressure gradient,and reducing the density ratio of the two phases.