Study on Cuttings Transport Mechanisms and Structural Design Optimization of Cuttings Bed Remover in Extended Reach Drilling

Summary Extended reach drilling (ERD) is an advanced technique that achieves broad reservoir coverage by significantly extending the well’s horizontal reach. However, drilling these long, high-angle sections faces a significant challenge—wellbore cleaning. Traditional wellbore cleaning strategies form the foundation of hole cleaning by optimizing parameters such as rate of penetration (ROP), drillstring rotation, and fluid rheology. In the demanding context of ERD, however, the cleaning capacity provided by these methods alone may be inadequate to manage cuttings in long horizontal sections, calling for enhanced cleaning techniques. The deployment of cuttings bed remover (CBR) to mechanically disrupt persistent accumulations has proved to be an effective solution. The CBR disrupts the structure of the cuttings bed by generating a high-intensity spiral flow field and alleviates the cuttings accumulation caused by gravitational settling in low-flow velocity zones. However, the underlying mechanisms governing the structure-performance relationships require further systematic investigation. To this end, we develop a 3D flow model by coupling computational fluid dynamics (CFD) with the discrete element method (DEM). Meanwhile, we simulate the migration and sedimentation behaviors of cuttings in the annulus by considering the coupling effect between the drilling fluid and cutting particles, thereby systematically analyzing the influence of the CBR on the morphology, thickness, and removal efficiency of the cuttings bed. Based on the simulation results, the action zone of CBR can be divided into the intense agitation zone and the intense transport zone, with swirl strength and transport intensity used as quantitative evaluation indicators, respectively. Moreover, we discuss the effects of drillpipe rotational speed, CBR structural parameters, and annular flow velocity. Compared with rectangular-type CBR configurations, the deflection-angled CBR design demonstrates marked superiority in performance of generating swirl, exhibiting enhanced generation capacity, although potentially incurring more pressure loss. With this study, we introduce an innovative method for delineating the operational zones of the CBR and quantitatively assessing its effectiveness, thereby establishing a robust theoretical framework for evaluating the impact of CBR. By analyzing swirl intensity and effective action distance in the high-agitation zone, the key parameters of CBR are optimized as blade height (25–27 mm), length (1.5 m), count (4–5), and inclination angle (30–40°). Additionally, a multiunit short-CBR configuration outperforms a single long-unit design.