Review and Perspectives of Energy-Efficient Methane Production from Natural Gas Hydrate Reservoirs Using Carbon Dioxide Exchange Technology

Natural gas hydrates are unconventional abundant hydrocarbon energy resources that can guarantee energy sustainability with little environmental impact. The solid nature of the resource, distinct thermodynamic characteristics, and accumulations at shallow depths make the existing conventional production techniques unviable. Among all the currently explored production techniques, the hydrate-based carbon capture and sequestration (HBCCS) technique is expected to improve production, proven to be geomechanically safer, and conceptualized to be environmentally friendly. In this carbon-neutral production concept, carbon emissions are effectively sequestered for the long-term. This review presents a comprehensive overview and perspective of the CO2 exchange-based approach to extract methane (CH4) from naturally occurring gas hydrate reserves, emphasizes its prospect as a suitable alternative according to the current energy demands and climate concerns, establishes its environmental and production challenges, and demonstrates the recent developments. This review focuses on the production aspect and discusses the mechanism of the exchange process, experimental and modeling studies, various in situ production tests using different techniques on multiple sediments, and production challenges associated with the exchange process. The aspects of geomechanics and possibilities of fracturing in hydrate reservoirs are also discussed elaborately. A suitable and effective technique is yet to be established to produce natural gas commercially by addressing the existing challenges like sand production, seafloor stability concerns, marine ecosystem problems, low production rate, uncontrolled dissociation, water production, etc. Although the CO2 exchange-based method is thermodynamically favorable, rapid crystallization of CO2 restricts mass transfer and prevents continuous exchange. The exchange process is also influenced by heat, salinity, residual water saturation, exchange gas composition, injection phase, injection pressure, sediment properties, etc. There is a need to study the CO2–CH4 exchange process at a fundamental level and at a larger scale, to understand its intricacies. In tandem with comprehensively discussing the subject, this review has listed the issues that require tenable solutions, which shall be helpful to readers who wish to work on production from CH4 hydrates using the CO2 exchange process. Methane hydrates shall be one of the strategic energy sources to meet our growing energy requirements for a sustainable future.