The double-connection structure of bionic joints of mining drill pipes has solved the problem of drill drop caused by fatigue cracks. However, with low-melting-point elastic–ductile alloy filling in the bionic joint, the thread on the joint cannot be hardened by high-temperature surface hardening treatments such as quenching and nitriding, making it prone to thread gluing or excessive wear. In this paper, the feasibility of diamond-like film deposition on the surface of a bionic drill pipe thread was studied. A tungsten transition film was used to improve the thickness of the film and the interfacial bond strength between the film and the substrate. The test results show that the total thickness of the DLC film is about 3~5 μm, the roughness is less than 2 μm, the hardness of the film reaches 24.4 GPa, the friction coefficient is 0.04, and the critical load is 56 N. SEM and EDS analyses show that the tungsten film and the bionic joint thread form a metallurgical structure. The morphology of the diamond-like carbon film is uniform and dense, and there is no obvious stratification between the substrate material. The joint with a diamond-like coating treatment has a longer service life than joints receiving conventional high-temperature nitriding treatment.

Efficient gas drainage in soft coal seams is commonly impeded by two coupled issues: coal-fines-induced clogging of screens and boreholes, and instability of the borehole wall. To overcome these limitations, an in situ grouted porous polyurethane system was developed for borehole completion. The polyurethane slurry, consisting of isocyanate, polyether polyol, catalyst, foam stabilizer, cell-opening agent, cross-linker, and water as a blowing agent, was formulated to coordinate foaming and gelation kinetics. By adjusting the type and dosage of catalyst, the gel time could be precisely controlled within 10–1500 s to suit different construction requirements. After curing, the material exhibited an interconnected open-cell structure with a porosity of approximately 83%, permeability greater than 4 D, and a uniaxial compressive strength of about 1.72 MPa. Mercury intrusion porosimetry revealed a highly connected, multiscale pore network, with an accessible porosity of 78.9%, a median pore size of 125 μm, and a dominant pore-size range of 1–301 μm, indicating favorable conditions for gas flow. Flow-through experiments under simulated methane drainage showed that coal-fine production is strongly dependent on flow rate: fines generation was negligible at flow rates ≤20 L/min and became noticeable at around 30 L/min. Scanning electron microscopy confirmed that coal fines were confined to the upper ~5 mm of the consolidation layer, where bridging and straining within small near-surface pores limited deeper penetration. Although near-surface fines deposition reduced permeability from the intrinsic polyurethane value (~4.0 D) to ~2.0 D, the permeability stabilized above ~1.5 D under dynamic conditions. Overall, these laboratory-scale results demonstrate that the porous polyurethane can effectively intercept coal fines within a shallow surface zone, provide sufficient mechanical support to stabilize the borehole, and maintain high permeability under the tested conditions, suggesting its potential as a candidate material for enhancing methane drainage performance in soft coal seams. Further field validation and comparative studies against conventional completion systems are needed to assess its true engineering viability.