Report: APP CMHS Project 1




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3.1.6. Outburst Control

Current Technologies

Outbursts of coal and gas have resulted in fatalities in Australian coal mining operations, predominantly due to asphyxiation from high gas levels or severity of the resultant over-pressure. Preventive measures focus on draining the gas. The gas in a coal seam has to be drained below an established threshold value of gas content, based on an Australian Standard, prior to the extraction of the seam.

The main factors that influence outburst are: gas content, gas pressure, geological anomaly, stress and material properties. Therefore the prediction of outbursts involves the measurement of each of these factors and their interaction.

Prediction of outburst potential involves interpretation of geology, indices, monitoring, geophysical data, gas content and environment determination. Seams with complex geological structures (particularly thrust faults, normal faults with throw of greater than full seam and strike slip faults) are more prone to outburst if high gas conditions are prevalent. Seams with pore size <75μm are more likely to outburst.

The main index used is the Hargrave’s emission rate – measures the gas emitted from coal samples in a tube on a flat plate (with no back pressure). Increases or decreases in gas levels can be an indicator of possible outburst. Geophysical methods are used to identify potential geological anomalies. Techniques such as: Seismic surveys for the detection of faults; logging of in seam boreholes to identify mylonite; magnetic surveys to locate dykes; and Radio Imaging Method (RIM) to identify faults and hard to drain gas zones. In a gas environment the most important factors are gas pressure, permeability and content. Gas content, being easier to measure is the most used indicator of potential outburst and at a critical value of ~7 m3/t for CO2. The ‘Quick Crush’ Direct method of gas content determination is predominantly used to ascertain the content value. Real time methane monitoring of returns has been used with some success in the past as an indicator of impending outburst.

The primary means (engineering control) for the prevention of outbursts is through the removal of the underlying hazard by gas drainage. A formalised management review meeting occurs (in this case involving the Mine Manager, Technical Services Manager, Geologist, Surveyor, Driller and/or Gas Drainage Engineer) at regular time intervals at each mine with outburst potential, to review the data obtained in the prediction phase in order to authorise mining to occur and to generate an Authority to Mine permit. Similar protocols (meetings to review data and authorise mining to continue) are applied where there is a high potential hazard with the potential to affect the safety of personnel.

The mitigation of personal injury due to outburst occurrence now focuses on the use of automation to remove all personnel from the suspected area. The use of personal protective equipment such as high strength enclosures and breathing apparatus is only used as a secondary measure when all other controls are in place and personnel must enter the work area.

More detailed descriptions on prediction, prevention and control are provided at the University of Wollongong Outburst website (http://outburst.uow.edu.au/).

Application Sites

This technology has been applied to the outburst-prone mines in Australian. Successful application of the technologies can be found at BHPB’s West Cliff and Appin mines in New South Wales, Peabody’s North Goonyella mine and Anglo Coal’s Central and Grasstree mines in Queensland.

Technology Gaps/Needs

  • Technology to drain gas in soft or structured seams such as application of coiled-tube drilling.

  • Technology to drain gas in seams of low permeability such as hydrofracturing, nitrogen injection and mineral leaching.

  • Technology to detect the geological structures ahead of mining, such as faults and associated pulverised coal.

  • Water jet drilling combined with tight radius drilling applied to multiple seams.

  • Development of analytical software to provide improved interrogation of conditions and quantitatively model the occurrence of outbursts.

  • Development of more comprehensive and practical indices reflecting the occurrence mechanism of outbursts, such as those incorporating gas and stress conditions.


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