Drill cuttings transport and deposition in complex annular geometries of deviated oil and gas wells: A multiphase flow analysis of positional variability

In this study, the two-fluid Eulerian-Eulerian multiphase flow model in ANSYS Fluent (v17.1) is adopted for the simulation of cuttings transport in a deviated annular geometry using two different non-Newtonian drilling fluids (described using the power law and Herschel- Bulkley models). The Syamlal-O'Brien interphase momentum exchange coefficient is implemented to capture non-spherical effects of the drill cuttings. The analysis conducted is based on the hypothesis that a position-dependent profile evaluation is expected to yield more insight into the transport process compared to a volume-averaged analysis over the entire flow domain. This is because the adopted simulation approach takes into account the microscopic particle properties which significantly affect the overall particle transport mechanism. However, this requires the application of robust postprocessing functionalities for data extraction from desired annular regions. Particle sizes considered are in the range of 0.002 m to 0.008 m with a sphericity range of 0.5 to 1.0. A rotational effect is incorporated in our model to describe the drillpipe motion in an annular wellbore with a vertical eccentricity of 0.6. The considered geometry contains a vertical, inclined and horizontal section with interconnecting upper and lower bends. The analysis of the particle velocity and concentration profiles revealed that the mud rheology, particle sphericity and particle sizes play vital roles in determining the cuttings removal process. It is particularly observed that the lower annular region of upper bend, is most susceptible to particle deposition with the lowest transport velocities observed. Our positional variability analysis has shown that the alternating dominance of nonspherical and spherical particles’ velocities significantly depends on the nature of the flow (i.e. dense granular flow or dilute annular flow in the upper and lower sections respectively).