Sustained production of gas hydrate through hybrid depressurization scheme with enhanced energy efficiency and mitigated ice blockage

Several trial productions have been conducted on marine natural gas hydrate reservoirs, demonstrating its enormous potential as an alternative energy source. Nonetheless, sustained and efficient production still remains challenging, with crucial issues on low gas production efficiency and blockages. The large amount of hydrate decomposition and resulting heat absorption can lead to prolonged subzero conditions close to the well; this can readily induce ice formation and blockage. This study aims to investigate the issue of ice blockages caused by insufficient energy supply during the recovery process. A systematic analysis of the energy consumption and ice blockage quantification at each stage of the traditional multi-stage direct depressurization and constant speed depressurization methods is conducted. A hybrid optimized scheme is proposed, which enhances energy utilization efficiency by appropriately utilizing reservoir sensible heat during the initial stage of production. Additionally, a multi-stage constant speed depressurization method is introduced in the later stages to mitigate production fluctuations and reduce blockage duration. Results showed a 69.5 % increase in energy efficiency and an average 67.1 % decline in gas blockage duration with comparable gas productivity. The proposed method could be a viable solution to mitigate challenges of icing blockages and fluctuating production during trial tests of marine hydrate reservoirs, achieving improved energy efficiency and sustainable production.