This paper mainly focuses on how to improve exploitation rate of coal bed methane (CBM) was presented in the paper. To enhance efficiency of exploitation of coal bed methane, the carbon dioxide or nitrogen gases were injected in the coal bed in the experiments. The injection of nitrogen gases in the coal bed could help increase the methane permeability. As a result, it showed that the injection of nitrogen gases could increase the stability and productivity of CBM.

1 Introduction

We are commonly known that coal bed methane gas, whose main component is methane, is generated in coal and associated metamorphism in the gas. CBM is extremely valuable in our country, and clean-energy, high heat and pollution, CBM will be the strategic energy that ranked number four after oil and gas. An abundant of coal bed methane resources in China, according to the latest and round of coal bed methane resource assessment results, within depth of 2000m the coal bed methane resources around China is total 36.81×1012 M3, equivalent to the coal of 520×108T, and equivalent to conventional natural gas resources on land rather, ranked the world's top three (Peiliang, 2007).

Coal is a rock of the porous medium containing a large number of pores and cracks, its surface is large enough, and coal can absorb gas molecules. CBM is mainly assigned to the adsorption state in coal rock. A large number of domestic and abroad of studies have shown that coal belongs to the adsorption of CO2 gas such as monolayer physical adsorption (Qinling et al, 2005). Coal is adsorption of gas molecules from different forces between the coal molecules and gas molecules, we are informed that including the Debye induction force and London dispersion forces. Due to the different gas molecules and the coal molecules forces are of different sizes. Therefore, the coals of gas components for different adsorption capacity are also different (Li et al, 2001).

The fact that displacing coal-bed methane gas (ECBM) technology is the use of competitive adsorption between the injected gas and CH4 gas indicates that it will promote desorption, and the displacement most CH4 from coal out. Multi-component mixed gases adsorption is significantly different from singlecomponent, but either Single or the multi-component gas mixture, the adsorption isotherms are the Langmuir equation (Baoan et al, 2005). The Diverse mixture of gas adsorption is between weak and strong adsorbs capacity.

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