Synchronous Inversion of Coal Seam Gas Pressure and Permeability Based on a Dual Porosity/Dual Permeability Model and Surrogate Optimization Algorithm

Rapid and accurate acquisition of permeability and gas pressure is crucial for gas development and disaster prevention in coal mines. However, these two parameters are currently challenging to obtain simultaneously using traditional testing methods. Moreover, due to the theoretical basis of the radial flow equation, most methods are only applicable to cross-seam borehole, which brings great limitations to the application of the methods. Therefore, this paper derives a new dual porosity/dual permeability model considering the impacts of time-dependent Fick diffusion, matrix mechanical and sorption strain. According to this coupling model and the surrogate optimization (SO) algorithm, a synchronous inversion method of the gas pressure and permeability is suggested. Then, the dependability of this method is validated by field tests. The findings demonstrate that, in contrast to other theoretical models and optimization algorithms, the new model can more precisely depict the actual change of borehole gas flow, and the SO algorithm can find a global optimal solution with higher accuracy in less time. Compared with traditional methods, the new method has the advantages of strong universality, short testing cycle and high automatic level. Therefore, this method has the potential to be an effective tool for obtaining coal seam gas parameters.