Research on the Interlayer Interference Law of Multi-layer Combined Mining in Low-permeability Gas Reservoirs

This paper focuses on the interlayer interference problem in multi-layer combined production of low-permeability gas reservoirs and studies the productivity laws of different lithologic combinations through physical simulation experiments. Three sets of single-layer and two sets of double-layer combined mining experiments were carried out on the sandstone cores of Qian 5 and He 4 and the 8+9# coal seam, and the gas production dynamics were systematically monitored. The results show that in the combined production system, the high-permeability layer significantly suppresses the medium and low-permeability layers, presenting the characteristics of "off-peak gas production" and production lag. The low-permeability layer was most disturbed. The gas production rates of the fourth layer of the double-layer combined mining middle box and the coal seam decreased by 14.02% and 32.27% respectively. The overall production capacity of the system has suffered a coordinated loss. The cumulative gas production of double-layer combined mining has decreased by 7.59% to 22.56% compared with the theoretical value of single mining. Mechanism analysis indicates that the high permeability layer dominates the bottom hole flow pressure system, resulting in insufficient effective production pressure difference in the medium and low permeability layers. The research results provide an important theoretical basis for the optimization of combined production in low-permeability gas reservoirs.