THMC-Coupled Numerical Modeling of Sand Production from Natural Gas Hydrate Production via Depressurization

Abstract

Natural gas hydrate (NGH) dissociation during depressurization-based production alters pore pressure and temperature, modulating effective stress, weakening the sediment framework, and yielding sand production. This leads to particle detachment, migration, pore clogging, and ultimately, fluid production instability. To understand the underlying mechanism, we propose a novel particle detachment criterion incorporating both critical water flow velocity and deviatoric strain and embed it into a fully coupled thermal–hydraulic–mechanical–chemical (THMC) model. The new approach has been validated at laboratory scale using Masuda’s depressurization experiments and at field scale against production data from the 2013 Nankai Trough offshore trial. Subsequently, a systematic evaluation was conducted to examine the collective effects of the intrinsic reservoir permeability, dissociation coefficient, and depressurization trajectories on multiphase flow and sand production. Results reveal a dichotomous relationship between intrinsic permeability and dissociation kinetics on the fluid production performance. Elevated permeability and rapid dissociation have been shown to enhance early gas production. However, these processes have also been demonstrated to intensify localized hydrodynamic drag and strain-induced particle detachment, thereby accelerating late-stage permeability degradation through deposition and compaction. Conversely, low permeability and dissociation severely impede pressure propagation while restricting sand mobility. The stability of the sediment is strongly influenced by the depressurization trajectories. Cyclic and abrupt pressure drawdown schemes amplify transient hydraulic disturbances and sand influx, whereas monotonic, fluctuation-minimized pressure pathways maintain bounded seepage behavior and improve long-term reservoir stability. It is therefore evident that effective field-scale NGH production design requires coordinated regulation of the depressurization strategy, dissociation progression, and permeability-specific flow redistribution to balance gas recovery and geomechanical integrity.