Numerical study on cuttings transport in vertical wells with eccentric drillpipe

In this paper, hydrodynamic of drilling mud and cuttings in a vertical well has been studied numerically. For solid-liquid two-phase flow simulation, the mixture model including continuity and momentum equations was used. To describe the rheological behavior of drilling mud, Herschel Bulky model was implemented. Then, a numerical code was developed to calculate flow field parameters (i.e. liquid phase velocity components, solid phase volume fraction, and solid phase velocity components in the annulus) and pressure drop. The results have been compared with available data in the literature and good agreement was found. Moving mud at entrance of the annulus and developed flow length were studied and pressure drop was calculated. Annular flow velocities in this study varied from 0.4 to 1.4 m/s. Then the effects of velocity, fluid type, pipe rotation, drilling cuttings and eccentricity on pressure drop were investigated. The pressure drop in the annulus increased while eccentricity and rotation of drill pipe increased. Rotation of the drill pipe shifts maximum fluid velocity location toward cornel space of the concentric annulus. After ensuring the accuracy of the simulation, the effects of drilling mud type, mud axial velocity, drilling rotation, fluid density and cuttings size on cuttings transport were studied. Finally, mud capacity for keeping cuttings was calculated in stasis. Then, with considering shape factor for cuttings, the velocity profile of cuttings, the mud capacity of the drilling flow and slip velocity were calculated. Slip velocity profile of cuttings in the annulus increased as cutting size increased. This indicates that cutting transport in the annulus enhances as velocity, mud density, viscosity and rotation of drill pipe increase. Eccentricity and cutting size have a negative effect on cutting transport.