Interactions between coal seam gas drainage boreholes and the impact of such on borehole patterns

Borehole drainage is the most effective means of extracting coal seam gas. However, numerous boreholes are usually needed to create strong drainage from a single coal seam. When multiple boreholes work at the same time, borehole interactions will occur, which strongly affect the gas production and the area controlled by each borehole. To accurately quantify the degree of interaction, this paper utilizes the changes in the gas pressure at points around the borehole to calculate the pressure decrease coefficients, which reflect the degree of disturbance between the boreholes. The relationships between the physical parameters of the coal seam and the pressure decrease coefficients are studied with a typical double borehole interaction model. The results illustrate that the pressure decrease coefficients are positively correlated with the coal permeability in the disturbance region. Furthermore, the relation between the pressure decrease coefficients and borehole separation forms a negative exponential function, whereas the relation between the pressure decrease coefficients and the distance from the borehole forms a positive index function. Multi-borehole patterns are also analyzed to investigate the ability of the pressure decrease coefficients to determine which common borehole pattern is most suitable for efficient gas extraction.