Study On Gas Desorption Characteristics Of Rich Heavy Hydrocarbon Coal Seam And Evaluation On Gas Content Measurement Value

Coalbed gas content is one of the most important basic parameters, and is the important parameter in calculating coalbed gas reserve, predicting mine gas emission and evaluating coal seams outburst risks. Direct method for determininging the gas content of the most commonly used method is the direct measurement in the mine. The factors that affect this approach are water, temperature, pressure, degree of coal metamorphism, and particle size, etc. But there is few studies of different gas components on the gas desorption characteristics. The methane content in the Coalbed Methane account for the majority, and the coalbed gas contains a number of nitrogen and carbon dioxide in the measurement of gas content in lab, they are the only test these three ingredients. So the existence of heavy hydrocarbon component could be ignored. The sum of concentration of these three components is also equal to or close to 100%. But in some special mine and well field, discovered that the gas containe heavy hydrocarbon component by 5%～25%. The heavy hydrocarbon as an important part of coal-bed gas is now can not be ignored. Effects of different gas components on the gas desorption laws are not the same. The C2H6 and C3H8 heavy hydrocarbon gases that have similarities with CH4 impact desorption rules. They also influence gas content measurement method and values.By measuring coalbed gas content of the Jiulishan Mine and the Niumasi Mine, writer analyzed the gas concentration of each component to determine the presence of heavy hydrocarbon components. First of all, the writer conducted experiments on coal methane and ethane desorption characteristics of single-component gas and compared desorption laws of different adsorption equilibrium pressure, coal samples and gas. The results are the single analytical capacity of two samples for methane and ethane increases with the increasing of speed of desorption. Under the same adsorption equilibrium pressure, the analytical capacity and the desorption rate for methane of anthracite in Jiulishan is more than them in Niumasi, ethane laws is the same as methane. Secondly, the writer conducted experiments on the desorption characteristics of the gases mixture methane and ethane. The results are adsorption equilibrium pressure and concentration that affecting the desorption characteristics of gas. Variation of the concentration of desorbed gas mixture meets the asorption model that coal surface is the heavy hydrocarbon, as the outer layer of coal is the light hydrocarbon.If the gas components affect gas desorption characteristics, heavy hydrocarbon gas mixture will affect the desorption characteristics. Based on the isothermal desorption characteristics of heavy hydrocarbon gas mixture, the researchers determined reasonably coalbed gas content containging heavy hydrocarbon and provided the basis for accurate measurement of gas content.