Appraisal of Gas Indicators from Goaf Drainage Holes for Spontaneous Combustion and Explosion Risk Management

In gassy underground coal mines prone to spontaneous combustion, goaf management is a challenging task to reduce the risks of gas explosion and spontaneous combustion to acceptable levels. Goaf gas drainage via vertical surface goafholes is a primary control method to manage gas emissions in Australian coal mines. However, the performance of vertical surface boreholes may be significantly limited by insufficient understanding of goaf gas flow and coal self heating behaviour, especially under intensive goaf gas drainage.

The efficiency and effectiveness of goaf gas drainage performance also varies significantly across different boreholes. In Australia, gas composition, flow rate and suction pressure are closely monitored in goafholes to assess drainage performance and manage gas explosion risk. To address the above challenges, this project used currently available monitoring data of gas indicators obtained from goaf gas drainage holes in three gassy longwall mines to identify the main triggers of premature closure for these goafholes. In these mines, CO and O₂ levels in drained goaf gas are normally adopted as triggers in goaf gas drainage Trigger Action Response Plans (TARPs). The effectiveness of these triggers was reviewed, along with other ratio indicators and temperature measured in captured goaf gas.

The key project outcomes are:

• Development of new methodology to manage and analyse goaf drainage data;
• An improved understanding of goaf gas profiles affected by goaf drainage;
• A proposed conceptual goaf gas and oxidation model under intensive gas drainage;
• A review of current goaf gas drainage TARPs;
• Goafhole gas flow rate analysis; and
• A theoretical model to calculate goaf resistance using goaf drainage data.