Interlayer Interference Mechanisms During Multi-Layer Commingled Production in Low-Permeability Gas Reservoirs

To investigate the interlayer interference mechanism during multi-layer commingled production in low-permeability gas reservoirs, this study focuses on the strongly heterogeneous reservoirs in the central Linxing area of the Ordos Basin. Laboratory-scale physical simulation experiments of commingled production were conducted on core samples from the Shiqianfeng (Q5) and Shihezi (He4) formations, along with the No. 8 + 9 coal seam. The gas production behavior, including the evolution of flow rates, the occurrence of staggered production peaks, and the resulting interlayer interference coefficients, was systematically analyzed and compared between single-layer and multi-layer commingled production scenarios. Experimental results reveal a positive correlation between cumulative gas production and layer permeability under single-layer production conditions. Specifically, the high-permeability layer (0.6470 mD) yielded 65.22 mL, whereas the low-permeability layer (0.1061 mD) produced 36.51 mL, representing a 44.02% reduction relative to the former. Under commingled production conditions, the productivity of the low-permeability layer exhibited more severe inhibition, showing declines in instantaneous production of 34.02–48.96% and cumulative production of 15.50–20.61%. These reductions substantially exceed those observed in the high-permeability layer, which ranged from 6.14% to 6.35% and from 5.00% to 8.76%, respectively. Furthermore, a greater permeability contrast results in a more pronounced difference in gas breakthrough timing. For a permeability ratio of 3, the breakthrough time difference reaches 191 s, compared to 131 s for a ratio of 2. The interlayer interference coefficient exhibits a negative correlation with the permeability contrast. When the contrast is 3, the interference coefficient for the low-permeability layer reaches 79.39%, representing an 84.51% increase relative to the coefficient observed at a contrast of 2. This indicates that larger permeability contrasts lead to more severe interference effects on low-permeability layers. These findings provide theoretical support for optimizing the efficient development of multi-layer commingled production in low-permeability unconventional gas reservoirs, highlighting the necessity of incorporating permeability contrast analysis in commingled production design.