Research On The Low Rank Coal Of Pore Characteristics And Desorption Laws

The exploration and exploitation of coal-bed methane(CBM) mainly concentrated in medium rank and high rank coal area presently in China. It's very weak the exploration and development of low rank CBM and the corresponding research technique. Low rank coal (Ro≤0.65%) is very extensive in china, such as xinjiang, Inner Mongolia, shaanxi, ningxia, qinghai. The pore structure of low rank coal is different of middle and high-order coal. The adsorption and desorption characteristics of coalbed methane also have different characteristics. Due to mining activities of frequency, mine gas became the biggest security hidden danger area.Therefore, it is necessary to low-level desorption characteristics of coal in-depth study.In order to study the CBM desorption characteristics of low rank coal, should be study reservoir characteristics first.Experiment mainly includes coal industry analysis, coal rock types of components, porosity determination, scanning electron microscope, mercury injection experiments (pore structure and pore characteristic), the liquid nitrogen adsorption experiment (specific surface area and pore volume characteristic), the isothermal adsorption experiments. Then we have to analyze the experimental data and do the isothermal desorption experiment and variable temperature desorption experiment, analyze laws of desorption and mathematical model.This is the basic to further study characteristics of diffusion and seepage.Through the experiments and analysis, the author summarized the conclusion. The pore of low rank coal is mainly constitute by big pore and secondary pore.Pore forms overall reflect semi-closed pore and fine bottleneck pore, partly reflect the characteristics of semi-closed pore. Surface is mainly distributed in the 5-6nm and 50 ~ 60nm. The adsorption ability of low rank coal overall below the medium rank and high rank coal, and the adsorption ability of lignite below long-flame coal. Weibull function is a fitting function for the adsorption curve fitting of low rank coal. The CBM desorption rate of low rank coal is higher than the medium rank and high rank coal. The curve fitting degree of Weibull function is the highest for low rank coal desorption. Finally, the paper analyzes and summarizes the CBM adsorption / desorption influencing factors of the low rank coal.