A critical analysis of gas data in relation to gas drainability in the Bulli seam

To prevent the outburst fatality, outburst threshold limits was established. It is the stipulation of limits on seam gas content prior to mining. The outburst threshold limits varied linearly based on gas composition, increasing from a minimum in CO2 rich conditions to a maximum in CH4 rich conditions. It is believed that the gas data of the drainage boreholes are closely related to the gas drainability in Bulli Seam. A total of 519 sample results from Metropolitan mine has been examined. It was found that Q1, Q2 and Q3 components increased in response to increasing measured total gas content QM. Statistical analysis also shows an increasing trend in the Q1:QM and Q2:QM ratio corresponding to increased QM, but there was a decrease in trend in the Q3:QM ratio corresponding to increased QM. A power relationship was considered to more accurately represent the average of each gas content component relative to QM, especially for “Fail” samples. The average value of CO2 composition of “Pass” samples is 73.5 % and it was 82.6 % for “Fail” samples. The zone with CH4/ (CH4+CO2) ratio of less than 0.2 includes 171 “Fail” samples, accounting for 88.1 % of total “Fail” samples.