We investigated three coal-bed methane (CBM) reservoirs in which there exist, when we are careful about data quality and reduce environmental variations, inverse correlations between methane content and the elastic properties of the coal beds. Such inverse correlations may exist in general in high- and medium-rank CBM reservoirs. There is evidence that supports the generalization of such inverse correlations and factors that distort them. These distorting factors may prevent identification of such inverse correlations in certain CBM prospects; however, they cannot negate the underlying inverse correlations. Such inverse correlations may play a role in CBM amplitude versus offset (AVO) similar to the role played by Gassmann-Biot theory (Gassmann, 1951; Biot, 1956, 1962) in AVO technology for conventional gas reservoirs. This may lay the first brick for a theoretical basis of CBM AVO.
