Currently, China boasts abundant shale gas resources. However, in the process of flowing production, there remain significant discrepancies in our understanding of the flow patterns of gas and water, and many challenges persist in gas–water measurement. Given the dense pore structure and complex micro-features of shale gas reservoirs, this study proposes a method to estimate the fractal dimension by utilizing shale mercury injection curves based on experimentally determined relative permeability curves, thereby enabling a more accurate fitting of these curves. Experimental results show that the two-phase co-infiltration zone in the shale is narrow overall, with bound water saturation exceeding 50%. The findings indicate that the experimentally measured relative permeability curves closely match those fitted using the fractal dimension approach. Moreover, the lower the permeability, the more the equal-permeability points of the fitted curves shift toward the lower-right quadrant. Overall, the fitting performance is satisfactory, providing additional research directions and insights for determining relative permeability curves of gas and water in shale gas reservoirs.

During depressurization-driven shale gas production, methane migration and state transformation in nanopores affect the source composition of produced gas. However, the relative contributions of initially free and initially adsorbed methane remain difficult to quantify at the molecular scale. In this study, we develop a Frame-0-based source-tracing framework for methane recovery in an idealized graphene square nanopore using molecular dynamics simulations under a stepwise depressurization protocol. Radical Voronoi local density and a two-component Gaussian mixture model are used to assign one-time initial labels to methane molecules at Frame 0. PID–preserving cross-frame tracking is then used to quantify the stage-wise and cumulative source contributions from the two initial populations. For the representative case of R = 10 nm and T = 353.15 K, the stage-wise fraction from the initially free population decreases from 79.5% to 62.2% as pressure decreases, while that from the initially adsorbed population increases from 20.5% to 37.8%. Increasing pore width mainly enhances total recovery through the contribution of initially free methane. Increasing temperature improves the contributions from both populations, with a stronger effect on initially free methane. The present results provide a molecular-scale quantitative characterization of methane initial-source attribution under the current stepwise depressurization protocol and establish a source-tracing framework that can be further extended to more realistic pore models.