Multiscale Numerical Simulation Of Fluid Flow In Digital Core Of Porous Media

The study of fluid flow in the reservoir rocks of oil and gas reservoirs is an important research content in the field of oil and gas reservoir development.With the development of CT scanning and imaging technology and the improvement of computing power,more and more researchers are interested in the pore-scale flow simulation based on digital core technology.However,for reservoirs with pore-throat size distributed on different scales,conventional digital core simulation is difficult to understand the rule of fluid flow in complex reservoirs.To solve this problem,a multi-scale fluid flow simulation method is established based on multi-phase digital core and a single-equation coupling of free flow with seepage.Single-phase flow simulations are conducted in multi-scale digital rock,and the impact of sub-resolution porosity of digital rock on permeability and the influence of multi-scale structure of digital core on the flow law is studied.The specific contents and results are as follows:(1)The multi-phase digital core including pore phase,rock phase and mixing phase is established by using CT scanning image and multi-threshold segmentation method.Based on the volume averaging method,a mathematical model of free flow with percolation coupling is established,that is,the Darcy-Brinkman-Stokes equation.(2)The finite volume method is used to discrete the Darcy-Brinkman-Stokes equation,and a multi-scale flow simulation program is written in C++ language.The blockMesh tool is used to discrete the three-phase digital core,which can characterize different phase distributions.The SIMPLE algorithm is used to solve the discreted Darcy-Brinkman-Stokes equation by comparing the SIMPLE algorithm with PISO algorithm.Direct numerical simulation and multi-scale flow simulation are conducted on two dimensional porous media model,which verify the validity of the multi-scale flow simulation program.(3)The multi-scale flow simulation based on the three-phase digital core shows that the sub-resolution porosity of digital core will seriously affect the connectivity of the flow channel and change the percolation capacity of the core.(4)The simulation results of the influence of multiscale pore structure on core percolation show that under the same pressure gradient,the percolation velocity increases with the increase of pore radius.The percolation curves of different scales in the digital core have Darcy linear flow characteristics.With the increase of pressure gradient,the percolation velocity of larger scale area grows faster.