Fugitive mine methane
In Australia, fugitive methane emissions from coal mining and handling and decommissioned mines represented 5.3 per cent of Australia’s total net GHG emissions in 2017.
Methane is also a serious safety concern in coal mining, for methane is explosive at a concentration between 5-15%.
The most effective and economic way to control methane emissions is to proactively capture methane by means of boreholes before methane enters the mine workings.
However, a successful methane capture system, marked as consistently stable flow with high methane concentration, can be hard to achieve.
Many variable add complexity to managing mine methane including:
- methane desorption processes under the impact of mining
- the magnitude and extent of methane emission
- methane flow dynamics and its interactions with mine ventilation systems, and
- the stability and integrity of methane capture boreholes under the dynamic strata deformation processes.
With mines increasingly operated at greater depth, this complexity is elevated.
Understanding complexity for mine methane management
We have developed a suite of technologies to obtain in-depth understanding of mining induced rock, groundwater and gas interactions.
- stratigraphy and reservoir characterisation on a scale of mining study
- field investigations of rock, groundwater and gas behaviours using various geotechnical instruments and tracer-gas techniques
- coupled geomechnics-reserviour modelling using our unique code of COSFLOW to predict methane emission scenarios at various mining parameters
- improved prediction of methane emissions taking account the production rate, and
- advanced simulations using computational fluid dynamics (CFD) techniques to investigate goaf gas flow dynamics and capture options.
We have built extensive collaboration with mining companies in various countries including Australia, China and India to work together on methane emission issues.
This collaboration gives us the opportunity to understand the rock, groundwater, and gas interactions in various mining conditions which in turn enhances our capabilities to address even more complex problems.
Our insights into the coupled rock, groundwater and gas interactions have led to innovative methane capture systems developed specifically to tackle the various coal mine conditions.
Delivering significant reduction in fugitive methane emissions for miners
We developed an innovative methane capture system with Glencore.
The system, using underground directional boreholes, was developed for the mine to replace its conventional vertical wells.
This has delivered significant benefits at a mine in the Hunter Valley in New South Wales, including:
- an increase in methane drainage efficiency from about 60% up to 80%
- a capability of net annual reduction of GHG to 0.42 Mt CO2-e, and
- savings in excess of $10M per year from increased productivity.
We also development of an integrated extraction system of coal and methane through a 10-year long collaboration with China’s Huainan Mining Industry (Group).
This system delivered an effective solution to address both excessive methane emission and outburst (a violent ejection of coal/rock materials and gas) issues in low-permeability, multi-seam mining conditions.
Optimising the mining sequence to enable an effective destress mining method in addition to the adoption of methane capture methods was key to these successes.
The magnitude and extent of the de-stressing effect was characterised and quantified to guide the design of the co-extraction system with large-diameter surface wells used to harmonise methane capture with coal production.
A four-year demonstration project at a coal mine of the Huainan Mining Group had demonstrated the success of the system resulting in:
- an increase of 85% in the total volume of methane captured per annum
- an increase from 19% to 45% in the volume ratio of methane utilisation to the total methane captured
- reduced outburst risks and methane concentration levels at the workings, and
- a total reduction of fugitive emissions by 0.73 Mt CO2-e over the project duration.