Evolution Of Pore-fractures Of Coal Reservoir And Its Impact On CBM Microcosmic Flow

In this dissertation,multiple regular experiments including coal composition,porosity and permeability,low-temperature N₂ adsorption/desorption?77K?,mercury intrusion porosimetry and field emission scanning electron microscope?FESEM?were conducted based on the acquired coal samples from 52 coal mines of 3 coal-bearing basins.Furthermore,some innovative experiments and relevant numerical simulation works were also constructed,including FIB-SEM for 3D quantitative characterization of nano-pores,X-ray?-CT for 3D quantitative characterization of micrometer scale pore-fractures and TG-MS combined with SEM analysis.Firstly,the multilevel evolution of pore-fractures of different rank coals and its heterogeneity were investigated.Secondly,the multiporous diffusion model was established under the restriction of multilevel pore system.And then the coupling relationship between the heterogeneity of pore-fracture and permeability was analysed.Finally,the gas content and CBM controlling model of Gujiao Block were discussed.To better understand these results and achievements,the detailed discussion are as follows:?1?The development characteristics of adsorption-pores?<100 nm?and seepage-pores?>100 nm?of different rank coals were quantitatively characterized by comprehensively applying various methods,and then its formation mechanisms were clarified.Moreover,the FIB-SEM and?-CT methods were combined to analyze the development characteristics of different scale pore-fractures in 3D space.A 2D and 3D quantitative characterization technology system was established for the multilevel pore-fracture system.?2?The morphological heterogeneity of pore-fractures,the pore structure heterogeneity of adsorption-pores and seepage-pores were calculated by different fractal models.The combined effects of coal rank,coal composition and pore-fracture structure on these fractal dimensions were revealed.?3?The CBM diffused in the complex pore system was divided into three stages:1)fast diffusion in the early period;2)transitional diffusion in the mid-term;and 3)slow diffusion in the later stage.Meanwhile,the multiporous diffusion model was established for applying to the multilevel pore system of coal reservoir.The effects of moisture and pressure on the CBM diffusion capacity of different stages were clarified.?4?Based on the fractal dimensions and porosity of seepage-pores,the coupling model of seepage-pores heterogeneity and permeability was established.The results indicated that the seepage-pores contributed permeability was much less than the cleat?fracture permeability.Then the effects of coal rank and pore structure on the seepage-pores contributed permeability were investigated,namely,the seepage-pores contributed permeability has an exponential negative correlation with coal rank and a positive correlation with the pore volume of seepage-pores and the proportion of mesopores and macropores.?5?The main controlling geological factors of gas content of Gujiao Block were investigated and the comprehensive gas control model of“tectonic-hydrodynamic-burial depth-sealing ability of overlying strata”was revealed in Gujiao Block.Moreover,the application of the multiporous diffusion model in the coal core site desorption was revealed and the characteristics of CBM desorption-diffusion and its main controlling geological factors were clarified.