Experimental Investigation of Borehole Sealing Efficiency in Coalbed Methane Extraction Using Controllable Slow-Release Materials

The inadequate sealing of extraction boreholes significantly reduces gas extraction efficiency and hinders the effective prevention of gas disasters. This study presents a novel sealing material with adjustable slow-release properties. The seepage and sealing performances of materials with different mix ratios were tested to determine the optimal formulation. The underlying mechanism was further analyzed based on the materials' physicochemical characteristics, and field experiments were conducted to validate the leakage control effectiveness of the controllable slow-release sealing material, thereby elucidating its mechanism for enhancing borehole sealing performance. The results indicate that the controllable slow-release sealing material with a water-to-material ratio of 4:1 performs best. The material consists primarily of montmorillonite, which is rich in SiO₂ and Al₂O₃, and exhibits excellent permeability and sealing characteristics. The nano-oxides, in cooperation with the surfactant, impart the slow-release blocking properties to the material. Initially, the material exhibits low viscosity, with excellent fluidity and permeability, allowing it to infiltrate the microfractures of the coal seam. As the injection time increases, the cross-linking agent within the material progressively reacts to form a polymer gel with a defined strength. In addition, the material can obstruct newly formed fissures during the continued expansion of coal body fractures, thereby demonstrating an effective dynamic blocking performance. These findings provide reliable technological support for the continuous sealing of coal seam fractures and efficient gas extraction.