Gas content estimation using initial desorption rate
The measurement of gas content plays an important role in mine safety and mine planning for coal and gas recovery. A number of methods exist to determine gas content; direct and indirect methods. The direct method of fast desorption test is the preferred method of gas content measurement. The indirect methods are based on either empirical correlations or laboratory derived sorption isotherms. Recent research has identified two new, semi-direct methods of estimating total gas content using early stage gas desorption rate measurement. Both techniques, if adopted, can provide operators with an indication of gas content and particularly whether the content is above or below the outburst threshold limit. A total of 930 samples, were analysed from two local mines, with known gas drainage problems and high degree of variability in both the insitu gas content and composition. Two specific aspects of the analysis included; the relationship of the three gas content components, Q1, Q2 and Q3, and the initial gas desorption rate relative to total gas content. Based on the relationship between desorption rate and total gas content, it was possible for minesite technical staff to provide operational personnel with an estimate of maximum expected total gas content from a particular core sample, based on the initial desorption rate value determined from Q2field measurement data collected by the drillers or site geologists.