Coal Adsorption Isotherms, Gas Content and Geological Controls of Bide-Santang Basin in China

The adsorption isotherms of Bide-Santang Basin’s main coal seams is studied based on analyzing two Coalbed Methane (CBM) wells in Huale exploration region and testing the coal samples and the major geological factors are also discussed. A conclusion has been made that the adsorption capacity of Bide-Santang Basin’s main coal seams is high. The Langmuir volume (VL) of dry ash-free basis range from 17.69 m3/t to 21.38 m3/t and the average is 19.46 m3/t. The methane saturation of the coal reservoir is lower than 100%, commonly ranging from 75.04 to 105.55% and the average is 84.51%. It indicates that coal reservoir in the research area is undersaturation. The critical desorption pressures are between 1.22 MPa and 9.1 MPa and the average is 3.25 MPa. The coalbed methane theory recovery rates are between 19.96 and 46.15% with average of 34.51%. The main effect geology factors on the adsorption in this area are reservoir pressure, depth of burial, degree of coalification and characteristics of pores. The reservoir pressure and depth of burial are positively related with the gas content. The higher of the degree of metamorphism is, the stronger adsorbability of CBM is. The well-developed micropores and mesopores contribute to the adsorption capacity of CBM.