| In this dissertation, multiple regular experiments including coal composition, vitrinite reflectance, mercury porosimetry, low temperature N2 adsorption(77K), porosity, permeability, isothermal CH4 adsorption and scanning electron microscope were conducted based on the acquired coal samples from 109 coal mines of 5 coal-bearing basins. Furthermore, some innovative experiments were constructed, including small angle X-ray scattering for adsorption-pores investigation, nuclear magnetic resonance(NMR) for seepage-pores research, X-ray CT scanning for fractures evolution and coupling experiment of seepage- acoustic emission-ultrasonic for fluid response under the circumstance of triaxial stresses. Firstly, the gas controlling mechanism for Yanchuannan area and southern Qinshui area were investigated. Secondly, the evolution mechanism of pore and fracture structure were stuided. Then the fluid response mechanism was investigated during the evolution process of pore and fracture. Finally, the mechanism of coalbed methane(CBM) production for the CBM reservoir with thermal treatment was discussed. To better understand these results and achievements, the detailed are as follows:(1) The geologic parameters that affected CBM were analyzed for Yanchuanna area and southern Qinshui area, which reveals a comprehensive gas controlling mode of coal thickness, burial depth, water sealing and shallow anticline in the Yanchuannan area, and a superposition gas controlling mode of syncline and hydraulic retention in the southern Qinshui area.(2) Based on the quantitative analysis of coal pore structure, the pore structure evolution mechanism was clarified; the results showed that the N2 adsorption at 77 K combined with SAXS was used to acquire the closed adsorption-pore volume. Pore structure evolution was affected by multiple factors including temperature, pressure, moisture, ashes, macerals and metamorphic degree. Adsorption capacity of pore depends on pore size and its surface complexity.(3) The thermodynamic evolution of pore structure was clarified, which shows that porosity increased with increasing thermal increment. However, it has differential increase rate. The fluid dynamics response during pore structure evolution reveals that the thermal impact on coal reservoir permeability decreased with the increasing coal rank. Furthermore, the coupled permeability model refers to gas adsorption, thermal expansion and effective stress was established.(4) The acoustic change and mechanical response mechanism evolution during fractures evolution were revealed, which shows that the fractures generation is closely related to the mineral interface inclination(bounded to 50°) and the memory effect was found during fractures evolution. Acoustic emission during fractures evolution has two phases: 20% of the maximum principal stress and 80% of the maximum principal stress, fracture clusters were constructed. X-CT was used to quantify the fracture porosity evolution, and a fracture permeability prediction model was established based on effective stress and fracture porosity.(5) The petrophysical parameters’ change of coalbed methane reservoir during thermal treatment was illustrated, which shows that the impacts of thermal dynamics on permeability and adsorption capability of high rank coal reservoir are lower than that of medium-low rank coal reservoir. Numerical simulation was conducted to analyze the CBM production for the coal reservoirs gone through thermal treatment. The results showed that the stable gas production time of CBM wells is in the order of high rank coal, medium rank coal and then low rank coal. From the perspectives of CBM industry development, the thermal treatment for improving CBM productivity is more valuable for high rank coal than that for low or medium rank coal. |
PDF Full Text Request