Abstract：Carbon dioxide is one of the main greenhouse gases. Geological disposal of carbon dioxide in coalbeds is regarded as an economical approach because of the mutual benefit of greenhouse gas sequestration and recovery of coalbed methane by replacement. In the past，most of works were focused on either theoretical analyses and numerical simulations，or experiments of adsorption and desorption of different gases on coal grains in size of millimeters or the less. In this paper，the experimental study results of carbon dioxide storage and methane replacement in coal specimens of large size(100 mm×100 mm×200 mm) are presented，which realistically simulates the process of the greenhouse gas sequestration and methane replacement in coalbed. In the experiment，the permeability of coal specimen is measured firstly with methane and carbon dioxide respectively；and it is found that the permeability of coal is different for the two gases. The permeability for carbon dioxide is larger than that for methane two magnitudes at least under the testing condition. There exists a negative exponent relationship between the permeability and applied body stress on the specimen. Under the simulated stress condition in the experiment，17.47 to 28.00 units of carbon dioxide can be stored in per unit of coal；and the replacement ratio of carbon dioxide to methane is as large as 7.03 to 13.91. The processes of injection，adsorption and desorption，replacement，and output of gases can proceed smoothly under the given pressures；the percentage of methane in the production gas can be amounted to 20% to 50% at the early stage and still can be maintained at the level of 10% to 16% even at the last stage during the experiment process. It is concluded that the effects of carbon dioxide storage and methane replacement are determined by several factors including injection replacement pressure，injection amount and velocity，methane content in the coalbed，and the development of pores and fissures in the coalbed，etc.. During the process of carbon dioxide injection and gas replacement，coal body swelling can be found with comprehensive effects of gas adsorption and desorption，and the deformation of coal framework. The research is expected to provide certain illuminations for practice of carbon dioxide disposal in coalbed or methane replacement recovery by carbon dioxide in the future.
