Numerical study of coal reservoir and borehole parameters evaluation considering temperature and multi-borehole...

To reveal the effects of temperature on the effective extraction radius and coal reservoir parameters during gas extraction in bedding boreholes, a hydraulic-mechanical coupling model (HM) and a thermal-hydraulic-mechanical coupling model (THM) for borehole gas extraction are established. The impact of temperature effects on the effective extraction radius, coal seam permeability, and gas pressure under single-borehole conditions are analyzed. Based on the mechanism of extraction superposition effect in multi-borehole extraction, the variation patterns of extraction superposition effect with key borehole parameters under borehole group conditions is explored. The results show that the model considering temperature effect shows a gradual increase in coal seam permeability, while ignoring temperature effect will overestimate the gas pressure drop and underestimate the permeability of the coal seam. Using the extraction superposition effect as the criterion for evaluating extraction effectiveness, the smaller borehole spacing and the larger diameter, the more obvious the extraction superposition effect between adjacent boreholes. The impact of extraction negative pressure on the borehole superposition effect is minimal. Under the premise of determining the effective extraction radius R for a single borehole, the superposition effect k is exactly 1.01 when the borehole spacing is 2.2R and the diameter is 95 mm in this model.