Advancement perspectives of CH4 recovery from methane hydrate reservoirs via N2/CO2-CH4 exchange: Experiments, simulations, and pilot test applications

Abstract

Despite significant progress in CH₄ recovery from CH₄ hydrate reservoirs via N₂/CO₂-CH₄ exchanges, critical research gaps persist, particularly in understanding the molecular mechanisms driving gas exchange under varying pressure and temperature conditions. Recent studies have focused on macroscopic outcomes, such as gas recovery rates, while neglecting the nanoscale interactions that govern these processes. In addition, there is a lack of integrated modeling frameworks that incorporate experimental data and simulation models to predict the mechanisms of N₂/CO₂-CH₄ exchanges. On the other hand, field-scale pilot-test applications have been limited, with few studies exploring the scalability of laboratory findings to real-world conditions, particularly in diverse geological settings. This review synthesizes insights from recent laboratory experiments, molecular dynamics simulations, and field-scale pilot tests, offering a holistic view of the N₂/CO₂-CH₄ exchange process. The findings revealed key factors influencing gas exchange efficiency, such as optimal gas mixtures, temperature, pressure, and sediment composition. Laboratory experiments have revealed that a balanced N₂/CO₂ gas ratio of 1:4 N₂/CO₂ can significantly enhance CH₄ recovery and CO₂ storage depending on the type and content of clay minerals present in sediments, particularly at temperatures around 274.2 K and pressures of approximately 10 MPa. However, other N₂/CO₂ ratios exhibit favorable performance under specific reservoir conditions. Specifically, a 41:59 N₂/CO₂ ratio achieves optimal results at slightly higher temperatures of 277 K–283 K and lower pressures of 7.1 MPa, 80:20 N₂/CO₂ effective at temperatures of 274.2 K–284.2 K and pressures between 7.1 MPa and 10 MPa. Also, the ratio of 0.77:0.23 N₂/CO₂ has been shown to enhance performance in conditions with lower temperatures of 261.2 K–284.2 K and moderate pressures of 3 MPa–7 MPa. Yet, challenges remain in optimizing these conditions for large-scale applications, particularly in heterogeneous geological settings. These findings highlight the need for further research to identify the optimal gas mixture ratio for different geological settings and operational conditions. Furthermore, advancing simulation models to capture complex gas dynamics in real-world reservoir conditions critical for refining predictions of gas exchange behavior were systematically presented in this research. The importance of pilot test deployments in fields such as Ignik Sikumi and Messoyakha was also discussed, showcasing the promise and challenges of scaling laboratory findings to real-world applications. Moreover, the potential for long-term CO₂ storage in hydrate reservoirs, with minimal atmospheric leakage risks of <1 %, were highlighted. Additionally, the review identifies key areas for future research and proposes potential interventions, including the refinement of experimental methods, the development of multi-scale models, and the integration of advanced monitoring technologies to enhance the scalability and environmental safety of CH₄ recovery technologies. The findings from this research are crucial for optimizing the efficiency and sustainability of N₂/CO₂-CH₄ exchange technologies by enhancing comprehension regarding screening, designing, and formulating N₂/CO₂-CH₄ exchange strategies.