How to Reduce Gas-Related Production Delays

Gas-related production delays can be reduced through gas reservoir modelling and emissions forecasting to support gas drainage design.

The process of excavating and mining coal causes fractures in the overlying and underlying strata. The fractures provide pathways for gas released from coal seams and other gas-bearing strata to flow into the mine workings. Coal seam gas typically contains high concentrations of methane with lesser concentrations of carbon dioxide. Low concentrations of other gases such as nitrogen, hydrogen sulphide and ethane may also be present in some coal seams. In certain geological settings, particularly in close proximity to geological structures, such as faults and dykes, the concentration of gases contained in a coal seam can vary significantly between methane-rich to carbon dioxide-rich.

In mine design and planning it is vital that mining engineers gather sufficient information to accurately determine the content and composition of the gas present in the coal seam and develop an understanding of changes in these parameters within the planned mining area.

The longwall method of mining coal causes fracturing of the overlying and underlying strata behind the retreating longwall face. Where coal seams and other gas-bearing strata are present within the caving zone, gas will be released from the strata leading to contamination of the mine workings. If the rate of gas emission exceeds the diluting capacity of the mine ventilation, the concentration of gas in the mine may exceed the statutory limit, resulting in production delays and potentially unsafe conditions.

The frequency of gas concentrations in ventilation air exceeding the defined statutory limit has increased, in part due to reduced expenditure on gas drainage but often due to a lack of understanding of the strata, gas reserves and gas emission potential into the mine workings. This results in development and production delays and avoidance of ‘difficult-to-drain’ areas. It is apparent that many operations are not effectively utilising gas reservoir and emission modelling to identify high gas emission areas and are not completing sufficient gas drainage in advance of planned mining. These production delays result in significant economic impacts.

The process of gas reservoir and emission modelling, in conjunction with the design of efficient and effective gas drainage, is an essential component of the mine planning process to control tailgate gas concentrations, reduce gas-related production delays, reduce fugitive emissions and ensure the continued economic success of your project.