The Micro-flow Simulation Of Spontaneous Imbibition Based On Lattice Boltzmann Method

Spontaneous imbibition is the main mechanism of tight oil production,and has become one of the important measures to improve oil recovery of the tight sandstone.The main factors affecting spontaneous imbibition are pore structure,wettability,oil-water interfacial tension and oil-water viscosity ratio.A lot of studies have been done on spontaneous imbibition by predecessors,but due to the limitation of computational speed,numerical simulation is mostly limited to two-dimensional research,and there are few studies on three-dimensional digital cores.The actual spontaneous imbibition process of core is quite different from the simplified two-dimensional model flow,and the two-dimensional model cannot reflect the distribution of fluid in the actual edge and corner well.In addition,there is no in-depth study on the influence of large and small pores on spontaneous imbibition,so it is not clear which pore has the greatest effect on spontaneous imbibition.In this thesis,the lattice Boltzmann method is used to simulate the spontaneous imbibition of oil and water in two and three dimensions,and the effects of pore structure,interfacial tension and fracture velocity on spontaneous imbibition are analyzed.The main work of the thesis is as follows:(1)Build a lattice Boltzmann model,through the MPI parallel computing to improve the running speed,and use the Poiseuille-flow,two-phase fluid wettability and single-capillary spontaneous imbibition to verify the accuracy of the model,which lay the foundation for follow-up study;(2)Build a two-dimensional consequent co-current spontaneous imbibition model,and analyze the factors of pore structure(e.g.,pore ratio and pore throat give etc.),the oil-water interfacial tension.It has been clear about the pore structure effects on the phenomenon of snap-off;(3)Build two-dimensional counter-current spontaneous imbibition model,and analyze the influence of pore structure,oil-water interfacial tension and the velocity of fracture on imbibition.It has been clear about the big pore and small pore in counter-current imbibition role;(4)By using the digital core,build the complex of the porous model,which make the dimension from 2D to 3D,and analyze the influence of interfacial tension on co-current and counter-current imbibition.In this thesis,through LBM simulation study,the effects of pore structure,interfacial tension and the velocity of fracture fluid on spontaneous imbibition have been clarified from the microscopic point of view,which is helpful to further understand the real fluid migration process in tight reservoir and provide support for guiding the efficient development of tight oil more accurately.