A Decomposition-Consolidation Model for the Production Behavior of Gas Hydrate-Bearing Sediments

Natural gas hydrates are the preferred alternative to traditional fossil fuels, estimated to store twice as much carbon. The gas hydrate-bearing sediment (GHBS) is a representative degradable soil. During gas hydrate production, solid mass loss and pore liquid/gas generation occur, including both decomposition and consolidation processes of GHBS. These potentially trigger reservoir collapse, severely affecting production safety. This study develops a decomposition-consolidation model for GHBS, quantifying the solid hydrate loss by the kinetic decomposition equation and describing skeleton deformation via both modified elasticity and volumetric strain relationships. By linking hydrate saturation with the representative parameters of hydrate decomposition, mass migration, heat transfer, and skeleton deformation, decomposition degree and consolidation degree are respectively introduced to assess these processes. The decomposing and mechanical parameters are calibrated through triaxial/modeling tests. Results show that consolidation degree and decomposition degree are not synchronized in sandy hydrate-bearing sediments, where depressurization-induced variation of consolidation degree predominates in the early stage, while the evolution of consolidation degree lags behind decomposition degree for temperature recovery after complete hydrate decomposition; hydrate decomposition-induced skeleton deformation, significant compared to pore pressure dissipation, remains crucial long after complete depressurization. These findings provide insights into optimizing safety of long-term gas hydrate production.