Improving the accuracy and precision of coal bed methane(CBM) estimates requires correction of older data from older coal exploration surveys to newer standards.Three methods,the depth gradient method,the contour aerial weight method,and the well-point aerial weight method,were used to estimate the correction coefficient required to predict CBM gas content from coal exploration data.The data from the Nos.3 and 15 coal seams provided the coal exploration data while the CBM exploration stages within the X1 well block located in the southern part of the Qinshui Basin provided the data obtained using newer standards.The results show the correction coefficients obtained from the two aerial weight methods are similar in value but lower than the one obtained from the depth gradient method.The three methods provide similar results for the Nos.3 and 15 seams in that the correction factor is lower for the former seam.The results from the depth gradient method taken together with the coal seam burial depth and the coal rank suggest that variations in the correction factor increase linearly along with coal seam burial depth and coal rank.The correlation obtained can be applied to exploration and the evaluation of coal bed gas resources located in coalfields.
Lei BoFu XuehaiZhou BaoyanShen JiaZOU MingjunFeng Qing
To help in ascertaining methane content of lignite reservoir in China,the isothermal ad-sorption measurements of methane have been performed on moisture-equilibrated coals of some typical lignite-bearing basins,which comprise maximum reflectance of vitrinite（Ro,max） ranging from 0.24% to 0.50%.Related to other coal properties,our analysis shows that methane adsorption of lignite is mainly affected by coalification,as well as by maceral composition,moisture content,and seam temperature.Maximum methane capacities of moisture-equilibrated lignite coals show a continuously increasing（and reasonably exponential） trend with increasing Ro,max.Methane adsorption capacity decreases with maceral composition besides the range 40%-60%,respectively.Moisture content shows discretely cor-respondence with methane capacity.Methane capacity also decreases as seam temperature increases,and its reduction increases with pressure under a certain temperature.
