Improvement of Thick Coal Seam Gas Drainage Efficiency Using Highly Pressurized Multidischarge CO2 Gas Fracturing Technique.

Abstract

Thick coal seam fracture stimulations were conducted to enhance pre-gas drainage efficiency through the use of a highly pressurized multidischarge carbon dioxide gas fracturing technique. This method also offers potential as a strategy for carbon dioxide sequestration, aiding in the reduction of atmospheric carbon dioxide levels and thereby contributing to the fight against climate change. This paper discusses findings from both field experiments and numerical simulations. Data from the field show that the multidischarge fracturing approach significantly improves permeability in thick coal seams, thereby boosting gas drainage effectiveness. Additionally, the impact of increasing the number of fracturing devices is more pronounced at distances of 2.5 or 7.5 m from the borehole but becomes more complex at 12.5 m or further. The numerical simulations reveal that this technique primarily enhances coal seam gas drainage by improving the seam permeability and establishing a gas pressure gradient within the seam. It is noted that the radius of failure around the borehole wall expands with higher discharge pressures, while the radius of effective drainage narrows as the gap between discharge heads increases. Moreover, adding more discharge sets significantly influences the deformation and permeability of the coal seam within a 5 m radius of the fracturing borehole, but the influence is not obvious after 10 m from the fracturing borehole.