Hole-cleaning performance in non-vertical wellbores: A review of influences, models, drilling fluid types, and real-time applications

The efficient removal of cuttings from all types of wellbore poses a substantial challenge. Hole cleaning (HC) depends on the physicochemical interplay between wellbore formations and drilling fluids (DF). Among the many problems encountered in complex wellbore trajectories, inefficient HC frequently occurs in deviated/horizontal oil and/or gas wellbores. The issue has attracted more attention as wellbore trajectories have become deeper, longer, and more complex. Inefficient HC can lead to major drilling problems including stuck or plugged drill strings, loss of circulation, slow rate of penetration, and formation damage. This review addresses the causes and consequences of HC and proposes strategies to mitigate them in all types of wellbore trajectories. The impacts of DF rheology and composition, and cuttings size, shape, and density on HC efficiency are identified. Drill-pipe rotation rates and various bottom-hole tools/drill-string configurations can be adjusted to improve HC. Experimental testing, field studies, and mathematical models, including computational fluid dynamics, are evaluated and their abilities to improve HC are established. Real-time models and indicators are playing an increasing role in the optimization of HC in deviated wellbores. Recommendations are made for future research required to further improve deviated wellbore HC performance and develop effective solutions to the remaining HC challenges.