Numerical Simulation Of Cuttings Migration Characteristics In Wellbore Based On Kinetic Theory Of Granular Flow

In the process of oil exploitation,there will be security problems caused by cuttings accumulation,so how to improve the migration efficiency of cuttings has become an important issue worthy of discussion in the drilling process.The cuttings migration in wellbore is a typical liquid-solid two-phase flow.Based on the Eulerian-Eulerian two-fluid model,this paper simulates the process of cuttings flow carried by drilling fluid under different working conditions.The sliding mesh method is used to realize the drill pipe rotation.The flow characteristics of drilling fluid and cuttings in wellbore were studied,and the interaction between cuttings was studied by the kinetic theory of granular flow.Considering the factors such as drill pipe eccentricity,inclination angle,drill pipe rotating speed and inlet velocity of drilling fluid,the flow behavior of cuttings was analyzed.The results show that with the increase of drill pipe eccentricity,more velocity vortexes are generated in the wellbore,which is not conducive to the movement of cuttings along the axial direction.It is not easy to produce cuttings accumulation in vertical wells.As the well inclination angle decreases,cuttings accumulation is more concentrated at the entrance,and the length of fixed cuttings bed is shortened.The influence of the change of well inclination angle on cuttings migration is greater than that of the drill pipe eccentricity on cuttings migration.As the rotation speed of drill pipe and the inlet velocity of drilling fluid are increased,the height of cuttings bed can be reduced within a certain range,and the migration efficiency of cuttings can be improved.Moreover,increasing the rotation speed of drill pipe and the inlet velocity of drilling fluid will increase the drag force between cuttings particles,increase the collision strength between particles,but reduce the collision frequency.Increasing the rotating speed of drill pipe in horizontal wellbore is more conducive to the destruction of fixed cuttings bed than increasing the inlet speed of drilling fluid.For vertical wells and inclined wells,increasing the inlet velocity of drilling fluid has a greater promoting effect on cuttings migration.Considering the influence of rheological parameters of non-Newtonian fluid power law model drilling fluid on cuttings migration efficiency in wellbore,the simulation results show that with the increase of consistency coefficient and liquidity index,it is beneficial to improve the migration efficiency of cuttings carried by drilling fluid and reduce the height of cuttings bed.As the consistency coefficient increases from 0.01 to 0.03,the volume fraction of cuttings decreases by 0.05864 in wellbore without eccentricity,and that decreases by 0.05497 in wellbore with eccentricity.As the liquidity index increases from 0.8 to 1.2,the volume fraction of cuttings decreases by 0.05814 in wellbore without eccentricity,and that by0.05696 in wellbore with eccentricity.With the increase of rheological parameters,the volume fraction of cuttings decreases linearly in the wellbore without eccentricity,while the volume fraction of cuttings decreases nonlinearly in the wellbore with eccentricity.By comparing the changes of turbulent kinetic energy,turbulent dissipation rate,the granular temperature of cuttings,solids pressure and solids viscosity,it is found that the change of liquidity index has the greatest influence on the fluid flow in the wellbore.