Numerical Study On Migration And Deposition Characteristics Of Micro Particles In A Fracture Channel

In the process of geothermal utilization,the migration and deposition of micro-particles caused by injection lead to channel blockage,which make injection difficult and reduce the heat-taking capacity of fluid from the ground.Aiming at the problem of channel blockage caused by injection,in this paper,the migration and deposition characteristics of micro particles in the fracture channel were studied by numerical simulation.The study is of great significance to reveal the blocking mechanism of the channel,prevent the clogging of the geothermal fluid seepage channel and improve the ability of heat transfer medium to take heat from the ground.In this paper,the fracture structure of geothermal reservoir was simplified to a two-dimensional fracture channel.By using Discrete Phase Model（DPM）,the migration track and deposition location of single particle in the fracture channel were simulated.The movement and deposition characteristics of single micro-particle in the channel were analyzed,including migration and deposition,translation in horizontal direction after settling to wall,and bouncing after settling to wall surface.At first,the effects of fluid velocity,fluid viscosity and density ratio of particle and fluid on the migration distance,deposition time and location of single particle were studied.Results indicated that:when the particle mass was smaller and the fluid velocity was slower,the particle deposited on the wall at the time of settling to the channel bottom;with the increase of fluid velocity and viscosity,the horizontal distance between the particle deposition location and the entrance of the channel increased;with the increase of the particle-to-fluid density ratio,the location of the particle deposition was closer to the entrance.Then,dimensional analysis of the main parameters affecting the distance of particle deposition points was carried out according toπtheorem.The main parameters include fluid velocity,fluid physical parameters,particle mass and particle release location.And the expressions of three dimensionless criterion numbers X,H,Lu were obtained.The simulation results were fitted to obtain the criterion relationship formula for determining the location of particle deposition:X（28）0.016?H^2.89L u^{-0.4 25}.Finally,the translation and bouncing of single particle after settling to the wall were studied.When the mass of particle and the flow velocity were larger,after settling to the wall,the particle continued to translate along the flow direction on the wall.This was mainly related to the fluid drag force on the particle and velocity of the particle reaching settlement point.When the particle mass and the fluid flow velocity continued to increase,the particle bounced after settling to the wall,and then failed to the wall,translated along the direction of fluid flow.This was related to Saffman lift force on the wall and the fluid drag force on the particle.Based on the researches of single particle migration and deposition characteristics,deposition behavior of multi-particles in the fracture channel was simulated.Results indicated that with the decrease of fluid velocity,the reduction of fluid viscosity and the increase of particle-to-fluid density ratio,the distribution of deposited particles on the wall became more concentrated.When the mass of particles and the fluid flow velocity were larger,multi-particles could accumulate when settling on the wall.