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Desorption and Carbon Isotope Fractionation of Coalbed Methane in Jincheng Area

DUAN Li-jiang1, TANG Shu-heng1, LIU Hong-lin2, LI Gui-zhong2, WANG Bo2   

  1. 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China; 2. Langfang Branch, Research Institute of Petroleum Exploration and Development, CNPC, Langfang 065007, China
  • Received:2008-09-20 Revised:2008-09-20 Online:2008-09-20 Published:2008-09-20

Abstract: The canister desorption experiments of the coalbed methane( CBM) from the coal samples of the Jincheng area were carried out, and the CBM desorption rate was calculated as 65.0% ~ 96.2%. The estimated recovery of coalbed gas well should be higher in this area. The CBM adsorption time is 0.33~8 d, which indicates that the CBM-producing well should reach a peak productivity in a short time. The CBM desorption process can be divided into two stages, the gas desorption rate is higher at the first stage and lower at the second stage. In the desorption process, the CBM carbon isotope tends to become heavier, but the tendency seems to be faster at the first stage and slower at the second stage. The CBM carbon isotopic fractionation during the gas desorption from coal reservoir might result in a fluatuation of δ13C1 value in well head in a narrow range. A longer period of fluctuation might mean a better exploitation stability and a higher production. Through the correlation analysis of the desorption amount and the carbon isotope value, the total gas desorption predicting equation was regressed, by which the producible reserves of the coalbed gas well can be predicted.