Investigation on interaction effects of multiple factors on clean gas extraction: implementation of response surface methodology

Abstract Gas-related disasters have become a major threat to mining safety of coal resources. Investigation into the optimization approach for inseam borehole gas extraction is important for improving extraction efficiency. By establishing control equations for coal seam deformation, porosity-permeability properties, and gas flow, effects of extraction time, initial gas pressure, initial coal permeability, and borehole diameter on gas flow pattern and effective extraction radius are analyzed. Based on response surface methodology and orthogonal experimental design, a regression analysis model of effective extraction radius and multiple influencing factors is established. Meanwhile, the interaction mechanism between effects of multiple factors is analyzed, thus identifying optimal parameters for gas extraction. Results show that effective extraction radius is positively correlated with initial permeability, extraction time, and borehole diameter, and negatively associated with original gas pressure. In terms of effect on effective extraction radius, those parameters could be ranked as follows: initial gas pressure, extraction time, initial coal permeability, then borehole diameter. Interaction between multiple factors could inhibit the impact of individual factors on extraction radius. An increase in initial gas pressure reduces the positive effect of permeability on extraction radius. Growing initial gas pressure inhibits the contribution of extraction time to effective drainage radius. Prolonged duration of extraction suppresses the positive effect of permeability on extraction radius. Interaction between initial gas pressure and initial permeability has the most significant influence on extraction radius. Results from orthogonal experimental design correspond to those of response surface methodology. These findings could provide guidance for dynamically adjusting drilling extraction parameters and improving gas-extraction outcomes.