Mechanical transitions in CH4–CO2 gas hydrates: molecular-level insights for sustainable energy recovery

The CH 4 extraction from gas hydrates via CO 2 gas replacement is a promising technique for energy recovery and reducing anthropogenic greenhouse gas emissions. A thorough understanding of the mechanical behaviour of hydrate reservoirs during gas replacement is essential to ensure the safety and economic viability of the approach. This study systematically investigates the mechanical properties of methane hydrates and their modifications due to CO 2 gas replacement using Molecular Dynamic simulations. Hydrate structures with varying CH 4 /CO 2 molar ratios were utilized to replicate the intermediate phases of gas exchange, allowing for an in-depth analysis of mechanical transitions. The results demonstrate that the mechanical response of gas hydrates is highly dependent on the guest gas type and composition. The mechanical properties of CH 4 -CO 2 binary hydrates reduce with increasing temperature due to the thermal weakening of H-bonds, but increase with increasing pressure. The thermodynamic criteria influence the mechanical behaviours of CH 4 -CO 2 mixed hydrates, while the effect of pressure on the fracture strength is minimal compared with temperature. The mechanical properties of hetero-clathrates lie between the characteristics of pure CH 4 and CO 2 hydrates. The introduction of CO 2 molecules induces mechanical weakening, which could be clearly justified by the reduction of H-bonds. Bulk modulus and shear modulus decrease while Poisson's ratio increases with CO 2 saturation through the disruption of hydrate lattice structure and cage instability. The findings suggest that the CO 2 replacement method improves the stability of CH 4 hydrates, ensuring the secure storage of CO 2 within hydrate-bearing sediments. • Molecular dynamics reveal mechanical behaviour of CH₄–CO₂ gas hydrates. • CO₂ incorporation disrupts H-bonds, softening hydrate lattice structure. • Temperature rise triggers brittle failure by destabilizing hydrate cages. • Pressure stiffens the lattice but has little effect on fracture strength. • Mixed hydrates enhance reservoir stability, enabling safe CH₄ extraction and CO₂ storage.