Study On Suspended Particle-liquid Twophase Flow And Heat Transfer Behaviors In Porous Media

Multiscale and multiphase flow and heat transfer in porous media widely exist in petroleum and natural gas engineering and geological engineering fields,etc.The migration and deposition of fluid-flow-driving suspended fine particles in pore throat will change the flow pattern inside porous media,resulting in pore clogging and reducing the permeability.Heat exchange among particles,porous rocks and pores fluids will also affect the temperature field of porous media.Therefore,the in-depth study on the behaviors of liquid-solid two-phase flow and heat transfer in porous media has important scientific significance and high practical value in the engineering application.However,research on the flow and heat transfer of suspended particles in porous media is scarce.Especially,the effect of the shape of non-spherical particles and the migration and deposition characteristics of binary mixed particles are still unclear.Besides,the influence of the aggregation and growth of fine particles on pore clogging should be further discussed.Therefore,in this work,CFD-DEM numerical simulation method,combined with the column experiments of particle migration based on X-ray CT tomography are used to reveal the liquid-solid two-phase flow and heat transfer behaviors,meanwhile,the formation mechanisms of pore clogging in porous media are further studied.This study can provide theoretical guidance and engineering application support in oilfield cuttings migration and recovery,oil well productivity decline and formation damage caused by pore clogging,etc.Based on CFD-DEM method,spherical particles-fluid two-phase flow models in porous media are given.On the basis of non-spherical particles,the multi-element particle model is used to construct ellipsoidal particle including three overlapping element spheres.The kinematic models of ellipsoidal particles considering the particle translational and rotational motions are established according to the element sphere motion information based on Newton’s second law and force-displacement law.By transferring the contact force at contact points on the sphere element to the center of ellipsoidal particles,the resultant force of contact forces acting on the particles is obtained,and the collision force models of ellipsoidal particle that suitable for the existence of multiple contact points are constructed.Aimed at the heat transfer between liquid and solid phase,DEM heat flow transport model based on the solid transient heat conduction coupled with fluid transient heat convection transport theory in the solid channel are presented.By introducing the mean fluid temperature,the three-dimensional coupling transient heat conduction and heat convection heat transport equations are proposed to established the liquid-solid two-phase flow and heat transfer model in porous media.Based on the spherical particle-fluid two-phase flow models using the volume average fixed coarse-grid fluid scheme and the coupling transient heat conduction and heat convection heat transport model,the liquid-solid two-phase flow and heat transfer behaviors in porous media at pore scale are analyzed by CFD-DEM method in combination with the configurational temperature in kinetic theory of granular flow(KTGF).On this basis,the effects of porosity,injected particle temperature,injected fluid velocity and suspended particle size are discussed.Simulation results show that the trajectory of suspended particles driven by fluid under collision is tortuous.The calculated Peclet number is less than 1.0,means that the heat transfer between the liquid and solid phases is dominated by heat conduction,supplemented by heat convective heat.The decrease of porosity and the increase of injection fluid velocity and particle size increase the heat exchange rate and heat transfer efficiency in pores,leading to a rapidly rise in the internal temperature field of porous media.Besides,the fraction of trapped particles and granular temperature are lower at large porosity,and the instantaneous axial and radial velocities of particles increase.Increasing the particle size and decreasing the injection fluid rate are conducive to the deposition of suspended particles,and most of the particles are mainly deposited near the inlet.Ellipsoidal particles are constructed based on discrete element method combined with multi element particle model,and the behaviors of ellipsoidal particle migration and deposition and fluid flow in porous media are studied based on kinematic models of ellipsoidal particles.Compared with ellipsoidal particles with the same volume equivalent diameter,the duration of non-uniform flow of spherical particles is shorter.Normal contact force and fraction of spherical trapped particles are larger than that of ellipsoidal particles,while the translational and rotational kinetic energies of spherical particles is smaller.In addition,the effects of volume ratio and density ratio on the migration and deposition of binary mixed particles were studied.The results show that with the increase of volume ratio,the proportion of fine particles increases,showing the tendency of particle agglomeration and deposition.The long-term residence probability and rotational kinetic energy of coarse particles decrease,while that of fine particles shows the opposite trend.With the increase of density ratio,the deposition pattern of fine and coarse particles changes from dispersion to aggregation deposition,and the total granular temperature decreases.The decrease of density ratio increases the particle translational and rotational kinetic energies,and the probability of particles staying for a long time is also reduced.Based on the X-ray CT tomography,the pore clogging behaviors induced by the migration of fluid-flow-driving suspended particles are studied by particle migration column experiments.The migration of particles is divided into the free migration stage,local clogging formation stage and pore clogging growth stage,and the permeability reduction rate decrease slowly at the free migration stage and quickly at pore clogging growth stage,respectively.In addition,the mechanisms of particle retention and pore clogging owning to particle aggregation and bridging caused by fluid viscosity,flow rate and suspended particles concentration are investigated.The reduction of normalized permeability caused by the formation of pore clogging and homogeneous distribution of suspended particles inside porous media are also studied.Results show that the critical fluid kinematic viscosity of local pore blockage is 52mm~2/s,and pore clogging pattern convert from local pore clogging to overall pore clogging when the suspended particles concentration increases from 0.5%to 1.0%.On the basis of experimental model size and parameters,by introducing the boundary condition of continuous particle injection based on based on CFD-DEM method,the migration,deposition,aggregation and growth characteristics of suspended particles in porous media are simulated targeted at particle free migration stage and local clogging formation stage.Besides,the effects of fluid viscosity,fluid velocity and suspended particle concentration on particle axial velocity,contact force,particle retention rate and average fluid velocity were investigated.Simulation results show that increasing the fluid viscosity,suspended particles concentration,and decreasing the fluid velocity increase the number of pores with particle aggregation and growth,thus increasing the probability of pore clogging in porous media.