Quantification and Mechanism of the Interborehole Effect in Coal Seam Gas Drainage

Abstract Coal seam gas drainage is crucial for reducing carbon emissions and ensuring safe coal mine production. In engineering, multiborehole combined drainage is widely adopted. However, the interaction among boreholes leads to the complex superposition of their respective influence zones. Previous research has largely focused on qualitative descriptions of this interborehole effect, while its quantitative criteria and underlying mechanisms remain unclear. Therefore, this study aims to establish a quantitative understanding of the interborehole effect and elucidate its mechanism, thereby providing a theoretical basis for optimizing gas drainage efficiency. To distinguish between the synergistic advantages and interference disadvantages within the interborehole effect, this study introduces two quantitative indicators: the content decrease coefficient (CDC) and the borehole interference level (BIL). Simulations based on a single-hole single-permeability model confirm that multiborehole arrangements significantly improve the gas drainage rate. The interborehole effect declines exponentially with increasing borehole spacing. The CDC exhibits pronounced variability under low permeability and low gas pressure conditions, whereas the BIL becomes more prominent under high-permeability conditions and increases linearly with initial gas pressure. Analysis reveals that the synergistic effect of multiborehole drainage stems from the gas-molecule diversion effect within the flow field, which enhances overall gas-migration efficiency. In contrast, the interborehole interference results from the superposition of flow fields, which reduces the gas-content gradient and consequently inhibits the drainage rate of individual boreholes. This study provides a theoretical basis for the design of borehole layouts. By rationally utilizing the interborehole effect, gas drainage efficiency can be effectively improved, thereby contributing to carbon emission reduction and maintaining safe coal mine production.