Submarine deformation monitoring during the second gas hydrate production test in the South China Sea

Natural gas hydrates, recognized as a promising 21st-century energy source, offer significant potential for low-carbon energy. However, the exploitation of marine natural gas hydrate may pose risks to sediment stability and may induce submarine deformation, necessitating environmental impact assessments. Current methods for monitoring submarine hazards are inadequate for long-term, in-situ assessments of strata stability. This study introduces an integrated submarine deformation monitoring instrument deployed during the second offshore natural gas hydrate production test in the South China Sea. The instrument captured variations in seabed static water pressure, azimuth, and tilt angles over a 183-day production period. By applying empirical mode decomposition and deformation field theory, the study reveals that only two monitoring stations recorded vertical settlements exceeding 1 cm, with a maximum of 1.98 cm, while others remained below 10 mm. This suggests the absence of severe geological disasters such as strata deformation or seabed collapse during the production test. The finding demonstrates the efficacy of the submarine deformation monitoring system combined with multivariate signal analysis for long-term, in-situ strata stability monitoring, which is essential for environmental impact monitoring and safety assessment of gas hydrate production.