Adsorption dynamic model of coalbed methane

Based on adsorption potential theory and gas state equation the model of the relationship between the coal reservoir pressure and coal adsorption radius, the model of the relationship between pore radius and coal adsorption capacity and the model of the relationship between reservoir pressure and coal adsorption amount are established, finally obtaining multi-parameter dynamic coupling change model which conclude reservoir pressure and adsorption capacity and pore radius. The model was verified by the use of coal structure testing data in Panzhuang block and isothermal adsorption test results. The results show that micropores whose pore size is less than 7.7nm are the majority in Panzhuang block. By critical point of pore size 7.7nm the pore volume decreased firstly and then increased. Calculation results of the model and isothermal adsorption curve of air-dried coal have high consistency, the starting point of the model is exhausted pressure and adsorption, the exhausted adsorption of Panzhuang block is 3m³/t. The model can not only calculate the adsorption of coalbed methane under the conditions of different temperature and pressure, but also predict the dynamic change of the adsorption during the production, these can improve the working system and recovery factor of coalbed methane.