Experimental Study of Different Gases on Permeability of Tectonic Coal

Abstract

Abstract In order to investigate the change law of different gas permeability of tectonic coal under circumstances of different gas pressure and different stress condition, take the tectonic coal with low permeability and outburst hazard as research object and study on the different gas permeability change law of tectonic coal in complete stress-strain process by using the triaxial servo-controlled seepage equipment for thermo-fluid-solid coupling of coal containing gas. The experimental results show that the complete stress-strain curve of coal containing methane is similar to that of coal containing carbon dioxide, which can be divided into five stages with unique characteristics respectively, and there are the minimum value of permeability corresponding to the neighboring juncture between stage II and phase III in complete stress-strain process. In addition, there are existing Klinkenberg effects not only for absorbing gas, such as methane and carbon dioxide but also for non-absorbing gas such as helium gas in the gas-bearing coal seam. Moreover, the Klinkenberg effect on the methane permeability of coal exists in all the stress condition of coal in complete stress-strain process and that on carbon dioxide permeability of coal only appears in the coal compaction named by phase I. Therefore, occurrence of Klinkenberg effect have something to do with structure of coal mass, but also are related to gas type and stress condition of coal mass.