The Theories And Experimental Studies Of Improving The Mining Rate Of Coal-bed Methane Through Gas Injection

Methane is the main harm of the safety and production of coal mine, which was the main gas causing greenhouse-effect and damaging the ozone layer. Meanwhile, coal-bed methane can change the coal-dominant unreasonable energy structure.of the our country as a new type of clean energy. Therefore, the exploitation of coal-bed methane is important from the aspect of safety, environmental protection and energy.The characteristics of the CBM of our country are low permeability,low saturation, low pressure and low recovery rate of CBM. According to the these characteristics, the thesis focuses on the improving the mining rate through the technology, which use carbon dioxide to replace CBM. Firstly,the characteristics of coal hole fracturing structure, occurrence state of the CBM, mechanism of migration and outputting, and adsorptive and desorptive features of CBM are studied. Then, the author does a research about the permeability of the methane and carbon dioxide. Through the experiment it can be concluded that permeability of coal are affected by volume stress and osmotic pressure. When the osmotic pressure is quantitative, the volume stress increases and the osmotic pressure reduces, which are caused by the deformation of the coal. When the volume stress pressure is quantitative, permeability changes as the increase of osmotic pressure, which is not drab but has a critical point. When the osmotic pressure is below the critical point, permeability reduces. When the osmotic pressure is above the critical point, permeability increases. All of these are caused by the value of the gas absorption. Meanwhile,the permeability of carbon dioxide is ten times more than methane. Finally, the author does experiments about the absorption of carbon dioxide, desorption of methane and forcing methane out with the injection of carbon dioxide. The experiment shows that the absorption curve and desorption curve are same in some degree. When the volume stress pressure is quantitative, the absorption capacity increases according to the increase of osmotic pressure. Under the same pressure, the absorption capacity of carbon dioxide is much more than methane. Their osmotic pressures are6MPa and7.5MPa, and their CBA desorption rate are36.9%and37.2%. From the experiment, it is clear that the desorption rate of coal has no relation with osmotic pressure, but related closely to the air containing of itself. When the forcing pressures are6MPa and7.5MPa, the mining gas injection rates are71%and73%, the CBA desorption rates are36.9%and37.2%, the increasing rates of mining gas injection are34.1%and35.8%, and the replacement ratios are6.7and6.1. The forcing pressure can improve the forcing rate in some degree. So it is clear that the production of coalbed methane can increased by35%by this technology. Meanwhile it can also bury the carbon dioxide in the coal-bed forever, reduce the environmental pollution caused by carbon dioxide, and reduce the gas explosion accidents.