The Experiment Study About The Mechanism Of Enhanced Coal Bed Methane Exploration By Super-Critical Carbon Dioxide And Its Application

In our country, the majority of coal mine is a high-gas coal mine. Because the CBM is the most serious disaster of coal mine, It will have significant impact on the safety of coal mine production. Just now the main method is gas drainage before Coal mining. A large amount of CBM directly diffuses to the atmosphere and it will cause serious pollution because of greenhouse effect. On the other hand, CBM is a energy resource, CBM and natural gas are composed of methane. It will reduce operating costs of coal enterprises to mining CBM by scientific and rational approach. If we effectively use CBM resources, it will not only protect the environment but also saves resources. More importantly, it is able to effectively improve the energy structure, to solve environmental problems caused by coal and energy crisis.In recent years, researchers have discovered a sophisticated extraction method of CBM and it is super-critical fluid extraction technology. super-critical carbon dioxide is a popular method for us in the process of CBM extraction. The so-called super-critical carbon dioxide, that is, the temperature is above thecritical temperature of 31.1℃and the pressure is above the critical pressure of7.38 MPa. In this situation, the density of super-critical carbon dioxide and liquid carbon dioxide is similar, the viscosity of super-critical carbon dioxide and gaseous carbon dioxide is similar. The diffusion coefficient of super-critical carbon dioxide is nearly 100 times higher than liquid carbon dioxide.super-critical carbon dioxide has not only the advantages of increasing CBM production but also strong ability to extract. super-critical carbon dioxide can extract some organic matter of coal seam. It can increase the size of the crevice tonicity and the diffusion pathways of gas and increase the permeability and recovery ratio of the coal seam. To this end, the paper carried out some basic experiments about the super-critical carbon dioxide, including coal permeability and adsorption and desorption experiments at different temperatures and stress.We also do flooding experiments of super-critical carbon dioxide and CT experiment. At last, we design a preliminary program of exploiting CBM by using super-critical carbon dioxide according to the geological conditions of an existing mine. In this paper, the main conclusions are:(1)When we do the permeability test, the permeability of coal samples showed a decreasing trend with the increasing of the volume of the stress at20℃, 40℃, 60℃ and 80℃ conditions. The permeability of coal samples initially decreases and then increases with the increasing of pore pressure at20℃,the permeability of coal samples have been increased with the increase of pore pressure at 40℃, 60℃ and 80℃. When the volume of the stress is 24 MPa,the critical temperature of maximum permeability is 60℃, When the volume of the stress is 30 MPa, the critical temperature of maximum permeability is 40℃.(2)When we do adsorption and desorption experiments, the pressure of the intermediate container include rapidly declining stage, steady declining stageand stable stage. The adsorption volume include rapidly rising stage, steady rising stage and stable stage. The volume of desorption include sharp desorption stage, smooth desorption stage and stable stage. The rates of desorption were34%, 46.5%, 54.1% and 59.4% at 20℃,40℃, 60℃and 80℃.It shows that the ability of adsorbed decline and the ability of desorbed rise with increasing temperature. It is good for the ability of desorbed to increasing temperature.(3)we do displacement experiment and the carbon dioxide pressure is8 MPa,the displacement efficiency are 58.3%, 68.4%, 75.6% and 81.7% at20℃,40℃, 60℃ and 80℃. super-critical carbon dioxide can extract some organic matter of coal seam. It can increase the size of the crevice tonicity of coal seam and the diffusion pathways of gas and increase the permeability and recovery ratio of the coal seam by CT.(4)We design a preliminary program of exploring CBM by using super-critical carbon dioxide according to the geological conditions of an existing mine. According to the project investment budget, we can learn that the initial investment of the project is 2.4 million and the profit of a ton of coal is24 yuan, but the cost of a ton of coal increase 19 yuan. after gas pumping, mine ventilation will be single lane,and it will reduce the loss of coal pillar, increase the amount of coal and reduce the cost of ventilation, therefore the program is economically feasible.