Uncertainty and Variability in Gas Desorption Measurements from Coal

Total desorbed gas content of coal is used to estimate economic potential of coal bed methane resources and to identify hazards for underground mine operations. Total desorbed gas analysis of coal samples have several sources of uncertainty related to different approaches to sample collection, analysis equipment, data processing and calculation methods. The largest uncertainties that arise could cause up to about 25% variation in the measured total desorbed gas content when using methods that are compliant with published analytical standards. Methods to minimize the uncertainties are well established, however are not always applied to data collection and analysis. In addition to analytical uncertainty, the total desorbed gas content of coal is variable between samples that are adjacent, even when robust and identical analytical methodologies are applied. We present data on the scale of analytical uncertainties related to different aspects of data collection for total desorbed gas content of coal from data collected throughout New Zealand over the last 15 years.