A numerical investigation of gas flow behavior in two-layered coal seams considering interlayer interference and heterogeneity

Abstract

Multiple-seam gas coproduction is a technology with potential to achieve economic targets. Physical experiments could replicate gas flow dynamics in two seams. In this study, numerical simulation was conducted based on physical experiments. Through calibration, the simulated results agreed with the experimental results. Three findings were obtained. First, the pressure distribution intrinsically depends on the depressurization effectiveness in each coal seam. The gas pressure difference and interval distance influence the pressure distribution by inhibiting depressurization in the top seams and bottom seams, respectively. Second, the production contribution shows a logarithmic relationship with the permeability ratio. The range of the production contribution difference grows from 11.24% to 99.99% when the permeability ratio increases 50 times. By comparison, reservoir pressure has a limited influence, with a maximum of 13.64%. Third, the interlayer interference of the top seams and bottom seams can be intensified by the reservoir pressure difference and the interval distance, respectively. The proposed model has been calibrated and verified and can be directly applied to engineering, serving as a reference for reservoir combination optimization. In summary, coal seams with a permeability ratio within 10, reservoir pressure difference within 1.50 MPa, and interval distances within 50 m are recommended to coproduce together.