Effectiveness of thin spray-on liners as a gas management tool in underground coal mines

Abstract

A thin spray-on liner (TSL) is defined as a chemical-based layer or coating (2–5mm) that is sprayed onto the rock surface to support the mining excavations. Besides ground support, TSLs can potentially be used as a gas management tool for underground coal mining. However, the permeability characteristics and effectiveness of TSLs at in-situ gas pressure are the key considerations in application of TSLs for gas management.This paper presents an experimental study to investigate the potential use of TSLs for gas management in underground coal mines. The coal samples were collected from an underground coal mine in New South Wales, Australia. The selected bituminous coal samples were initially characterised using petrographic and uniaxial compression strength (UCS) tests. Single phase gas permeability tests were then conducted on the coal samples. Methane (CH4) and carbon dioxide (CO2) were used for the tests as they are the gases of main concern in underground coal mines, and Helium (He) was used as a control gas to investigate the effect of gas adsorption on the coal permeability. Permeability tests were first conducted on coal samples before the TSL application. The coal samples were then coated with two types of TSL materials with a thickness of 5mm and the permeability tests were repeated. The experimental observations show that both TSLs are very effective in reducing the coal permeability, with the permeability values in the range of nanodarcies.High injection pressure gas flow tests were also conducted to investigate the amount of pressure that the TSLs can resist. The injection pressure was increased until the TSLs failed. The failure of TSLs was demonstrated by a sudden increase in the permeability. The test results show that the failure pressure of the TSLs is directly related to their adhesion strength on coal.