Adsorbed and Free Methane Production Behaviors of Deep Marine Shale from Real-Time NMR

Deep shale reservoirs, located at significant depths, feature complex pore networks predominantly composed of nanopores with diameters under 50 nm. However, substantial retention of hydraulic fracturing fluid within these nanopores during stimulation treatments significantly hinders shale gas productivity. Consequently, investigating gas flow behavior in shale matrix nanopores, with a particular focus on aqueous phase trapping effects, is essential. Real-time NMR analysis indicates that fine mesopores (2–10 nm) in deep shale formations serve as the primary methane reservoir, containing 69.88% of the total storage capacity. However, macropores (>25 nm) play a dominant role in methane production, contributing to 45.17% of recoverable free methane. Under aqueous retention conditions, the maximum methane recovery ratio from the shale matrix in the research area is 41.29%. This research quantitatively characterizes the magnitude and mechanisms of water-mediated impacts on methane migration dynamics through the integration of methane transport experiments and aqueous phase distribution analyses conducted under varying moisture conditions. Experimental observations demonstrate that aqueous phase obstruction in the pore-throat networks of the shale matrix significantly reduces methane flow efficiency and induces delayed desorption of adsorbed methane. The mechanistic understanding of multiphase flow dynamics in aqueous-saturated shale reservoirs is critical for developing predictive production models and optimizing enhanced recovery strategies to maximize hydrocarbon output in deep shale formations.