Discrete phase simulations of drilled cuttings transport process in highly deviated wells

Abstract

Transporting drilled cuttings from the bottomhole to the surface becomes more difficult and problematic in highly deviated wells than in vertical wells. Cuttings tend to settle down on the low side of the annulus typically in the form of a bed which can cause further problems. The height of this bed depends on many parameters such as annular domain geometry, drilling fluid density and rheology, annular flow rate, drill pipe rotation speed, cuttings size, shape, and their density. Prediction of the stationary cuttings bed height with respect to these aforementioned parameters is thus necessary to optimize the range of the controllable parameters for a desired level of wellbore cleaning. A computational setup that represents the spatial geometry of the cuttings transport domain, and utilizes discrete phase model coupled with numerical solution of the Navier-Stokes equations augmented by a turbulence closure model – SST version of k-ω is used for predicting the bed height of the stationary cuttings bed and moving cuttings velocities. Discrete phase model is a mathematical tool to navigate large number of particles in a flow field by calculating the particle paths in a Lagrangian frame by the time integration of force balance on each individual particle. Turbulence effects on the particle motion are also incorporated through a random walk model. The drag force on non-spherical particles is incorporated using a sphericity based correlation. Roughness of stationary bed surface is also incorporated through the modified law-of-the wall model. A snapshot technique is applied here in these simulations by computing flow solutions in the geometric domains with pre-defined stationary bed heights. The statistics of particle - wall collisions are analyzed over these geometrically pre-defined stationary bed surfaces to predict which domain would represent the equilibrium cuttings bed height. A systematic validation study is presented by comparing the simulation results against published experimental datasets for velocity profile estimation of non-Newtonian fluids flowing in turbulent regime, stationary bed heights, and moving bed velocities. Further, a parametric study is presented for the effects of wellbore inclination, fluid density and rheology, particle size and sphericity, inner pipe rotation and the inner pipe rotation speed.