Experimental investigation and analysis of frictional resistance between drill pipe and cuttings bed in horizontal wells

Abstract
Extended-reach horizontal wells are critical for unconventional hydrocarbon development, yet cuttings accumulation frequently induces excessive drag, pipe sticking, and drilling instability. Existing studies mainly investigate either cuttings transport or drill string mechanics independently, while the coupled evolution between cuttings-bed dynamics and drill pipe loading remains poorly understood. This study aims to clarify the fluid–solid coupling mechanisms governing drill pipe axial resistance during tripping operations in horizontal wells.
Here we show that tripping speed, cuttings-bed morphology, particle size, and drilling-fluid viscosity jointly control the nonlinear evolution of drill pipe frictional resistance. A visualized horizontal-well experimental platform was developed to systematically investigate the effects of cuttings bed height, bed length, particle size, tripping speed, and effective viscosity on drill pipe axial force. Results indicate that increasing bed height and tripping speed significantly intensify axial resistance because of annular flow restriction, cuttings compaction, and enhanced mechanical pushing effects. Particle size exhibits a distinct U-shaped influence on axial force, reflecting the transition from fine-particle adhesion to coarse-particle mechanical blockage. Compared with conventional empirical models, the proposed second-order response-surface model accurately captures multivariable coupling behavior, achieving an R2 of 0.9764 and a MAPE of 4.89%. The proposed framework provides theoretical and engineering guidance for drag prediction, hole-cleaning optimization, and safe tripping operations in extended-reach horizontal wells.