The Study Of Increased Permeability Law With Supercritical Carbon Dioxide Injected Into The Low Permeability Coal Seam

The vast majority of our high gas and outburst coal seam belongs to lowpermeability coal seam. The improvement of coal permeability, the development ofnatural gas in a green environmental protection way, has become one of the hottestacademic research topics. Coal has a typical double dielectric structure features. Makeuse of zero surface tension, low viscosity, high proliferation, strong dissolvent abilityand other characteristics of supercritical carbon dioxide to improve the permeability ofporous media. To study the flow law of supercritical carbon dioxide, we do someexperiments injects supercritical carbon dioxide into the low permeability coal seamsample. Based on the experiment results, we carry a further study to get the law of theinternal crack dynamic propagation and multi-physics coupling effect of stress field,seepage field and temperature field through numerical simulation while supercriticalcarbon dioxide is injected into the coal seam. The conclusions are as follows:(1) Use the manmade coal briquette to do the experiment and control thepermeability of coal sample’s orthogonal change with the temperature, pore pressure andeffective volume stress. Reveal the change rule of the coal samples permeability andpermeability coefficient to summarize the empirical formula of carbon dioxide densityand dynamic viscosity changing with the temperature and pressure.(2) By comparison of the coal macroscopic characteristics change during the actionof supercritical carbon dioxide, and the microscopic analysis of the variation regularityby CT scanning the section. The results show that supercritical carbon dioxide’sinjection can promote the coal sample’s pore crack development greatly, and it has agood effect on the improvement of coal seam permeability.(3) Using COHESIVE elements to simulate the coal level cleat system and monitorthe crack surface at a fixed point, reveals the law of pore pressure, crack openingdisplacement, and the dynamic regularity of crack surface in the fracturing processwhile supercritical carbon dioxide injected into the coal seam.(4)Establish the permeability change model of fracture system in the coal,andestablish the fluid-solid-heat coupling dual media mathematical model containing thecoal deformation, seepage and adsorption of gas according to the migration andadsorption characteristic of supercritical carbon dioxide in the coal seam. (5) Reveals the cleat distribution, generate a random fracture coal model through thecoal section digital image processing and statistical analysis of coal cleat system. On thebasis of the permeability and the permeability coefficient evolution rule fromsupercritical carbon dioxide antireflective experiments, develops the fluid constitutivemodel with the changing rule of the carbon dioxide density and dynamic viscositychanging with the temperature and pressure, and realizes random fractured coal bedfracturing antireflective fluid-solid-heat coupled three fields simulation analysis underthe action of supercritical carbon dioxide. Finally, reveals the changing rule of coalseam internal pore pressure, permeability coefficient, effective volume stress andtemperature in the process of gas injection.