Application of thin spray-on liners to enhance the pre-drained coal seam gas quality

Abstract

Gas drainage has been the most common technique for gas management in underground coal mines. This method involves drilling holes into a virgin coal seam to allow the gas bleed off from the coal into the drainage holes. A major problem with the underground gas drainage is the air leakage around the gas drainage hole that cannot be blocked off by the sealing material. The air leakage will cause the low concentration of the drained gas and decrease the efficiency of the gas drainage hole, which may further lead to many other risks, such as spontaneous combustion, gas combustion and gas explosions. A thin spray-on liner is defined as a chemical-based layer or coating (3–5 mm) that is sprayed onto the rock surface to support mining excavations. Since their introduction, thin spray-on liners have received some success as a ground support tool for underground mining. Besides ground support, thin spray-on liners also show some potential to be used as a gas management tool in underground coal mines due to their relatively low permeability. This paper describes a field trial of using thin spray-on liners for enhancing the gas drainage efficiency by blocking the fractures around the drainage holes. The project involves spraying a thin spray-on liner onto the area surrounding gas drainage holes whereby the thin spray-on liner acts as a thin membrane decreasing the permeability of coal. This restricts the air migrating through the coal seam and diluting the gas from the drainage holes. The key benefits associated with the application of TSLs are the increase in the methane purity and the decrease in the air contamination. In-situ adhesion tests were conducted in parallel with the gas tests, and the results revealed that the TSL tested could be implemented for underground coal mine applications as the main failure mode is the internal failure of the coal substrate.