Is CO2 Sequestration in Marine Hydrate Reservoirs Geomechanically Stable? 

Hydrate-based CO₂ sequestration in marine gas hydrate reservoirs is a promising dual-purpose strategy for carbon storage and energy recovery. However, geomechanical stability remains a critical challenge for ensuring safe geo-engineering operations, as it directly influences risks such as wellbore destabilization, subsea subsidence, and submarine landslides. Despite significant advancements, a systematic understanding of the geomechanical responses of marine hydrate reservoirs under CO₂ injection is still lacking. This study provides a comprehensive review of the formation stability associated with hydrate-based CO₂ sequestration, adopting a cross-scale and multi-method perspective. Three distinct storage strategies are discussed: (1) CO₂ sequestration above the hydrate zone, forming an artificial hydrate cap; (2) sequestration within the hydrate zone through immediate CH4-CO2 exchange; and (3) sequestration within the hydrate zone via later-stage replacement, producing mix-hydrates. We further evaluate experimental, numerical, and molecular-scale studies that investigate the geomechanical behavior of hydrate reservoirs across these scenarios. Key findings reveal several unresolved issues, including the debated mechanical superiority of CO₂ hydrates compared to methane hydrates and the absence of quantitative relationships linking hydrate saturation to reservoir mechanical performance. Additionally, commercial viability remains a significant hurdle, with integrated approaches such as the co-production of gas hydrates, shallow gas, and deep gas proposed as potential solutions. This review highlights critical knowledge gaps and identifies future research directions to advance hydrate-based CO₂ sequestration. By addressing these challenges, this work aims to support the safe and sustainable implementation of this emerging carbon storage technology.