Underground » Ventilation, Gas Drainage and Monitoring
The measurement of coal seam gas content has a significant impact on safety and operational efficiency within Australian underground coal mines. There is an expectation that reported gas content values are accurate and truly represent the gas content of the coal seam in the area from which the coal samples are collected.
In recent years, some Australian researchers and providers of commercial gas testing services have reported the potential for significant volumes of gas to be 'lost' from coal samples when the time required to recover and seal the sample into a desorption canister is prolonged. This view was adopted in the 2016 update of the Australian Standard for the determination of gas content of coal by the direct method (AS3980:2016) which states “significant errors will occur in the determination of lost gas if initial gas desorption is not measured within about 40 minutes of zero time”.
A new procedure has been developed to test the impact that extended core sample recovery time has on the accuracy of gas content measurement. The results of testing on core samples collected from thirteen separate locations among four Australian underground coal mines are presented and discussed. These results show no evidence of 'lost gas' and associated significant error in measured gas content due to extended core sample recovery time. The results do however demonstrate variability in measured gas content which is consistent with the findings of previous research investigations into interlaboratory variability and accuracy of gas content measurement.
The method used by one commercial gas testing service provider to establish correction factors to be added to the measured gas content of coal samples with extended recovery time has been investigated and discussed. The findings of this project demonstrate that such correction factors are not warranted and unnecessarily overstate the gas content of the coal seam from which the core sample was collected.
Instead of focusing on recovery time as a significant source of error in gas content measurement, mines and gas testing service providers are advised to focus on developing and maintaining rigorous and repeatable sampling and testing procedures to minimise risk of potential sources of error, listed in AS3980, from adversely impacting the accuracy of gas content measurement.