Experimental Study About Cardon Dioxide Displacing Coalbed Methane On Hydrostatic Pressure

Coalbed methane is an unconventional gas, which is self-generated and self-stored. It is one of the most potential energies with huge reserves in the past30years.China’s CBM resources are very rich, however, as the coal permeability is generally lower than industrial mining conditions, the application of conventional mining methods are restricted in our country. Based on the characteristics of CBM in our country, we suggest adopting the technology of displacing coalbed gas by carbon dioxide to enhance the CBM recovery; meanwhile, carbon dioxide can be stored in coalbed to reduce air pollution.In this master’s thesis, we first study and summarize the mechanism of gas’s sorption, desorption and migration, and analyze the effects of temperature, volume stress, gas pressure on gas storage and transport. In addition, we also make a theory research on the process of displacing methane by carbon dioxide in the coalbed. On this basis, we use large size (100mm×100mm×200mm) of meager-lean coal as samples to conduct permeability test on hydrostatic pressure and displacement test.The permeability test results showed that under the condition of room temperature, the gas in the coal is dually influenced by hydrostatic pressure stress and permeation pressure. When the samples are under a hydrostatic pressure, its internal variation of contraction distortion is uniform without shear failure; its physical characteristics are much closer to the isotropy porous media. From the regression analysis, we learn that when permeation pressure is constant, as hydrostatic pressure rises, permeability is attenuated in the minus exponential rule; when the volume stress is constant, the decrease of permeability gets minimal value, and then it began to rise with the increase of permeation pressure. The displacement test showed that as for replacement of methane by carbon dioxide, its replacement ratio is1.43-2.17.The volume stress gets lower, the replacement ratio gets higher. At the same time, the temperature has an important influence on replacement process; the higher temperature, the better replaced results. Under the different volume stress and displacement pressure, the three samples ’displacement efficiency are57.1%、40.3%、43.9%, it is dually influenced by volume stress and displacement pressure, and increases with the decrease of volume stress, drops with the rise of displacement pressure. Compared with previous works, we found that displacement pressure have a significant influence on displacement efficiency.