Interfacial mechanisms of bubble–driven capture and agglomeration of coal particles under micron confinement

To elucidate the pore-scale mechanisms of bubble-induced coal-fine transport, aggregation, and pore-throat blockage during coalbed methane (CBM) drainage and production, experiments were conducted to investigate the interactions between dispersed coal fines and static bubbles, shape-conserving migrating bubbles, and deforming migrating bubbles. Coal-fine capture, transport, and aggregation under the three bubble conditions were compared, and force analysis was combined with experimental observations to elucidate the underlying mechanisms. The results showed that the gas–liquid interface effectively captured and enriched dispersed coal fines. Static bubbles mainly captured nearby particles, whereas shape-conserving migrating bubbles rapidly captured particles upon interfacial contact and transported them along the migration path. When bubbles entered pore-throat constrictions and underwent pronounced deformation, changes in interfacial morphology further promoted aggregation of the captured particles. Quantitative image analysis showed that, within 5 s, the net interfacial enrichment increased by approximately 12.33 percentage points, while the mean equivalent diameter of the aggregates increased from 29.67 to 32.60 μm, corresponding to an increase of approximately 9.9%. The coupling between the Jamin effect and coal-fine aggregation promoted the accumulation, retention, and bridging of aggregates with sizes approaching or exceeding the local throat size, thereby increasing the risk of localized blockage. These findings provide pore-scale experimental evidence for optimizing CBM drainage and production by regulating production intensity and gas–liquid flow conditions to mitigate coal-fine enrichment, aggregate growth, and pore-throat blockage.