Self-sealing by secondary hydrate reformation governs sweep and permeability evolution during depressurization production

The formation of secondary hydrates during depressurization development of hydrates can have a pore-closing effect, limiting pore-scale connectivity, inhibiting mass transfer, and weakening sustainable methane production in marine hydrate reservoirs. This study combines pore-scale microfluidic visualization of methane hydrate dissociation and regeneration with reservoir-scale coupled simulations to quantify the hydrate cycle of dissociation-secondary hydrate reformation, clarifying how hydrate regeneration controls production characteristics and its impact on reservoir properties. Multiscale results show that an early rapid release phase is followed by a stepped, stagnant growth phase, consistent with the secondary hydrate reformation process. Increasing the initial pressure from 5.5 to 9.5 MPa increased the total gas production from 16.3 to 21.3 mL, but slightly decreased the recovery rate from 89.5% to 85.3%. At a constant pressure, increasing the initial temperature from 276.15 to 278.15 K accelerates complete dissociation but reduces cumulative gas production and recovery rate. Higher hydrate saturation extended the gas production duration from 60 seconds to 80 seconds, indicating that higher saturation levels result in higher methane production and longer duration. At the reservoir scale, secondary hydrate reformation reduced the effective sweep rate by partially decoupling the dissociation front from the pressure-propagation boundary. The early dissociation front was located approximately 45 m from the wellbore, migrating to approximately 90 m as vertical extension progressed, indicating a shift in hydrate migration paths towards gravity-driven preferential paths within the 42 m thick reservoir section. These findings quantify the reformation-controlled sweep behavior and provide constraints for pressure management during depressurization, with the aim of mitigating mass-transfer limitations induced by secondary hydrate reformation.