Dual-objective recovery: Methane extraction and CO2 sequestration in natural gas hydrates via molecular dynamics

This study explores the simultaneous extraction of methane (CH 4 ) from natural gas hydrates (NGH) in permafrost and marine environments, coupled with the sequestration of carbon dioxide (CO 2 ) as hydrates. This dual approach aims to achieve sustainable energy recovery and greenhouse gas reduction. Molecular Dynamics simulations were conducted to analyze the influence of temperature (270–285 K), pressure (6–12 MPa), and initial CH 4 hydrate saturation (75 %–100 %) on CH 4 -CO 2 gas replacement characteristics. These thermodynamic ranges were selected based on the CH 4 and CO 2 hydrate phase equilibrium diagram. Findings reveal a strong temperature dependence in the replacement process, with enhanced CH 4 recovery by 15 % at higher temperatures but decreased CO 2 storage capacity by 3 %, indicating a trade-off between energy extraction and sequestration efficiency. In contrast, pressure effects at constant temperature are minimal. High initial hydrate saturations improve CH 4 recovery but reduce CO 2 sequestration efficiency due to limited molecular mobility within the hydrate structure, resulting in higher CH 4 /CO 2 replacement ratios varying from 1.4 to 2.6. Additionally, the study examines the mechanical properties, including Young's modulus and fracture strength, of CH 4 -CO 2 hydrates post-replacement at 280 K and 8 MPa. The study offers valuable perceptions into CH 4 recovery using CO 2 gas and explores the mechanical behaviour of mixed hydrates. These insights are pivotal for advancing sustainable energy extraction and environmental protection strategies, particularly in utilizing gas hydrates as a resource while mitigating climatic impacts. • The mechanism of CH 4 -CO 2 replacement comprises CH 4 extraction and CO 2 sequestration. • The temperature has a prominent effect compared with pressure on CH 4 -CO 2 replacement. • The sequestration of CO 2 decreases with increased CH 4 hydrate saturation. • The mechanical properties of CH 4 -CO 2 mixed hydrates preserve the mechanical integrity of rock.