Wenbo Sheng

Stacked coalbed methane (CBM) reservoirs can increase the drainage thickness of a single well, but commingled production is influenced by stress-sensitive permeability, gas desorption, water drainage, and interlayer heterogeneity. This study presents a three-segment reservoir model for well GP-2 in the Tucheng block. Pore-fracture compressibility was estimated from overburden low-field nuclear magnetic resonance measurements and compared with stress-dependent permeability obtained by the pulse-decay method. The resulting coefficient was used in the dynamic permeability relationship and held fixed during history matching. The model was calibrated against gas- and water-production data from the first 240 d. One-factor simulations were then run over a common 3000 d calculation window to compare the relative responses to geological, adsorption, and stimulation parameters. In the GP-2 base model, average gas rate increased with equivalent coal thickness, gas content, Langmuir pressure, stimulated area, and stimulated-region permeability; inverse responses were obtained for cleat-fracture porosity, proportional three-layer initial permeability, initial reservoir pressure, and Langmuir volume. Adsorption time and interlayer spacing had comparatively small effects. These trends are specific to the selected model and parameter ranges and should not be interpreted as validated long-term forecasts or established causal relationships. This study demonstrates a practical way to carry a laboratory-derived stress-sensitivity parameter into a multilayer field model.

The dynamic process of water depletion plays a critical role in both surface coalbed methane (CBM) development and underground gas extraction, reshaping water–rock interactions and inducing complex permeability responses. Addressing the limited understanding of the coupling mechanism between heterogeneous pore water evolution and permeability during dynamic processes, this study simulates reservoir transitions across four zones (prospective planning, production preparation, active production, and mining-affected zones) via centrifugal experiments. The results reveal a pronounced scale dependence in pore water distribution. During low-pressure stages (0–0.54 MPa), rapid drainage from fractures and seepage pores leads to a ~12% reduction in total water content. In contrast, high-pressure stages (0.54–3.83 MPa) promote water retention in adsorption pores, with their relative contribution rising to 95.8%, forming a dual-structure of macropore drainage and micropore retention. Multifractal analysis indicates a dual-mode evolution of movable pore space. Under low centrifugal pressure, D₋₁₀ and Δα decrease by approximately 34% and 36%, respectively, reflecting improved connectivity within large-pore networks. At high centrifugal pressure, an ~8% increase in D₀−D₂ suggests that pore-scale heterogeneity in adsorption pores inhibits further seepage. A quantitative coupling model establishes a quadratic relationship between fractal parameters and permeability, illustrating that permeability enhancement results from the combined effects of pore volume expansion and structural homogenization. As water saturation decreases from 1.0 to 0.64, permeability increases by more than 3.5 times. These findings offer theoretical insights into optimizing seepage pathways and improving gas recovery efficiency in dynamically evolving reservoirs.