Numerical Simulation On Cuttings Migration In Vertical Annular Wellbore

The efficient migration of cuttings is one of the important problems in the research of wellbore cleaning and liquid-solid two-phase flow.The accumulation of cuttings in wellbore will cause a series of problems such as wellbore isolation and stuck pipe.In order to prevent the occurrence of hazards and further improve the oil field production and economic benefits,this paper adopts numerical simulation method to study the characteristics of debris migration under different operating conditions and physical parameters,studies the liquid-solid two-phase flow with Euler-Euler two-fluid model,and solves the flow problem with the standard turbulence model.The Gidapow drag force model is used to simulate the interphase forces.The operating parameters include inlet speed,drill pipe rotation speed and drill pipe eccentricity.The physical parameters include drilling fluid density,drilling fluid viscosity and particle diameter,and then the cuttings migration characteristics in the wellbore are compared and analyzed.The results show that the increase of inlet velocity,drilling pipe rate,drilling pipe eccentricity,drilling fluid viscosity and drilling fluid density all contribute to the optimization of cuttings migration.The increase of inlet velocity can effectively increase the axial velocity of particles and facilitate the upward flow of debris.With the increase of inlet velocity from 40cm/s to 100cm/s,the volume fraction of debris also decreases from 0.067 to0.047.Increasing the drill pipe rotation speed is helpful to increase the turbulence of the liquid phase in the annular wellbore and make the liquid and solid phase distribution in the wellbore more uniform.However,when the drilling pipe penetration rate increases to a certain value,the change of cuttings concentration in the annulus is very small,and the increase of drilling pipe penetration rate has little effect on the radial velocity of particles,with the change order of magnitude only 10^-3.With the increase of drillpipe eccentricity,the annulus flow field in the wide annulus region is more uniform than that in the narrow annulus region,but the drillpipe eccentricity has little effect on the debris migration behavior in the vertical wellbore.The increase of liquid density can improve the drag force of liquid on cuttings and the suspension ability of cuttings in static liquid,which is conducive to cuttings migration.The increased viscosity of the drilling fluid directly enhances the particle carrying capacity of the fluid.However,the increase of particle diameter is not conducive to debris migration.