Coupled Mechanisms of Methane Supply, Retention, and Self-Sealing in Natural Gas Hydrate Accumulation

Submarine natural gas hydrate accumulation requires deep methane to enter the gas hydrate stability zone, become immobilized within a reservoir, and remain confined beneath a caprock. The long-term coupling among reservoir supply, caprock retention, and hydrate self-sealing remains poorly resolved. We developed a mass-conservative synthetic two-dimensional Darcy flow and reactive-transport model that couples a quasi-steady potential field, mobile methane transport, supply- and pore-capacity-limited hydrate formation, and saturation-dependent permeability reduction. Single-factor, full-factorial, global-sensitivity, numerical-convergence, and long-term experiments showed that reservoir and caprock permeability both controlled methane supply; hydrate mass was more sensitive to caprock permeability (PRCC = 0.919) than to reservoir permeability (PRCC = 0.738), and the reservoir response plateaued above approximately 100 mD. Caprock permeability and thickness jointly regulate flux and leakage, with maximum conversion occurring at intermediate caprock permeability rather than at maximum flux. In the 30 kyr reference case, self-sealing reduced source-zone flow by 7.14%. In the 500 kyr extension, hydrate-mass growth and source-flow change first remained simultaneously below 1% over the preceding 10 kyr at approximately 338 kyr. The parameter combinations maximizing hydrate mass, conversion efficiency, and sustained accumulation differed, and, at 30 kyr under the stated thresholds, only 8 of 81 combinations jointly achieved high conversion, elevated reservoir saturation, and low leakage. Favorable accumulation therefore reflects dynamic matching among supply, retention, and self-sealing under specified boundary conditions, rather than an isolated extreme in any single property.