Evaluation of coal structure and permeability with the aid of geophysical logging technology

Coal structures and the associated permeability were studied by a combined investigation of geophysical logging data and well tests from coal reservoirs of Huainan and Huaibei coalfields in China. A large amount of the site observations on coal sections of mining faces and the macroscopic investigations on textures of drilling coal cores were carried out, providing experimental information for classification of coal structures. Geophysical log was implemented in 600 boreholes for exploration of coal and coalbed methane (CBM) resources, including 10 CBM wells which were used for permeability tests. The permeability tests were conducted by using injection/fall-off method. The results, together with the log data obtained from geophysical log technologies, have been analysed by using geological statistics, permitting correlation of the permeability of coal seams to the log responses. The correlation developed in this study provides better evaluation of coal reservoir permeability, resulting in an improved CBM exploration in the given coalfields.