Simulation of fracture and permeability of thin-interbed coal-bearing strata and analysis of geological mechanism

Large‑scale development of coal measure gas, as exemplified by the Walloon Group in the Surat Basin, Australia, reflects the superiority of thin‑interbed reservoirs. However, the fracture‑permeability coupling mechanism and its geological controls in such thin‑interbed composite reservoirs remain unclear. To address this gap, we carried out a physical simulation experiment of true‑triaxial stress‑permeability using different thin‑interbed configurations. The results showed that increased brittleness leads to more cracks in composite rock strata, and that the degree of fracture development in thin‑interbed‑like material was higher under tensile tectonic stress (vertical loading direction). Under identical stress conditions, the differences in fracture development among different thickness configurations are controlled by "uncoordinated stress‑strain of adjacent layers". Permeability increased with the lateral pressure coefficient and horizontal stress difference, governed by the degree of fracture closure under different stress states. The permeability of composite rock strata is strongly influenced by a pore‑fracture composite seepage system, which plays a key role in enhancing reservoir connectivity. These findings provide theoretical support for the development of thin‑interbed coalbed methane.