Retention mechanisms and collaborative material design of lost-circulation-control slurry in deep and ultra-deep fractured-vuggy loss channels： A CFD-DEM review

Abstract:

Deep and ultra-deep fractured-vuggy loss channels are characterized by abrupt aperture variation， rough walls， local expansion and strong distal connectivity， which may cause premature entrance sealing， deep material loss or erosion-induced failure of the plugging zone. To clarify the governing mechanism for the transition of lost-circulation-control slurry from transportation to retention，this review examines particle-scale CFD-DEM and related simulations published mainly during the past decade， with emphasis on computational domains， mesh size， time steps， boundary conditions， contact laws， fluid constitutive models and validation， and quantitative results are adopted for synergistic material design analysis.The results show that in a specific rough-fracture model with a ratio of particle diameter and fracture width （d/W）=0.4， a wall-friction coefficient of 0.5 and an inlet velocity of 0.1 m/s， an 8% particle volume fraction did not seal within 3 s， whereas 10% and 20% sealed at 2.6 and 2.2 s， respectively. A separate three-dimensional fracture study identified a model-specific favorable combination of particle size of 0.50~0.67 W， concentration of 8%， carrier-fluid viscosity of 50 mPa·s and wall-friction coefficient of 0.7~0.9. In a shape-memory-particle simulation for 2~5 mm fractures， increasing the inlet-outlet dimensions from 3 mm×2 mm to 5 mm×4 mm， increased sealing time from 0.11s to 0.25 s and loss ratio from 4.6% to 12.3%. A design combining absolute bridging dosage with gap-filling dense packing increased pressure-bearing capacity by 100%~229%， while reduced cumulative loss by 31%~38% and material consumption by 28%~76% in three comparative cases. These thresholds are conditional on channel geometry， particle shape and boundary settings and should not be treated as universal formulations. Based on this， a collaborative design workflow integrating channel parameterization， geometric gradation， carrier-fluid rheology， high-temperature functional retention and multiscale validation is therefore proposed， which provides support for the lost-circulation-control material transportation from empirical compounding toward computable and verifiable design.