Numerical simulation and experimental study of cuttings transport in intermediate inclined wells

Hole cleaning in directional well drilling must be monitored and properly controlled during the entire drilling operation. Hole cleaning for intermediate inclined wells is particularly difficult because of the dramatic change of flow configurations and the tendency of cuttings to slide downward. Inadequate hole cleaning for wells in this range of inclination angles can lead to a series of drilling problems.;A number of experimental studies are conducted using a full-scale flow loop to investigate the effects of different parameters on cuttings transport in directional wells. Four different solids moving patterns are observed in the tests: constant-bed flow, waved-bed flow, packed-dune flow, and dispersed-dune flow. A fluid-solid, two-phase flow pattern map is developed. The effects of fluid type, well inclination angle, ROP, mud rate, drill pipe rotation, and temperature on the cuttings concentration and the pressure gradient are studied.;The physical mechanisms which cause changes in the flow configurations are analyzed. Several transition criteria are proposed to detect the flow pattern boundaries. Mechanistic models are developed to simulate the cuttings concentration and pressure gradient for different flow patterns. Based on the flow pattern map and the mechanistic models, a program is developed to calculate the cuttings concentration profile and pressure profile along the entire wellbore.;A CFD-based solid-liquid, two-phase model is developed to investigate the details of the boundaries between the packed solids and fluid flow region and simulate the transient hole cleaning process. Simulations are conducted for cuttings flushing in different inclined wells. Cuttings back-sliding is found to have important effects in the cuttings flushing in intermediate inclined wells, which can lead to pack-off of the wells. Some practical recommendations are given for hole cleaning in intermediate inclined wells.;The effects of temperature on cuttings transport are investigated by conducting experimental tests under elevated temperature conditions. Temperature effects cuttings concentration for Newtonian fluids and non-Newtonian fluids differently. Changes in shear thinning property of the non-Newtonian fluids and the bonding between packed cuttings are found to be two important factors leading to the temperature effects on cuttings transport.