- China University of Mining and Technology, School of Resources and Geosciencs, Geophysics, China (ts24010074a31@cumt.edu.cn)
To assess the role of gas hydrates in global resources and the carbon cycle, it is crucial to estimate the volume of natural gas hydrate resources. Most hydrate resource estimates typically focus on methane hydrates. However, hydrate drilling at many sites in the South China Sea (SCS) has found Structure II hydrates containing heavier hydrocarbons, suggesting that methane hydrates may lead to an underestimation of the total hydrate resources. This study, based on the biogenic and thermogenic gases in the SCS, analyses three different gas compositions including 100% methane, 96% methane+4% ethane, and 86.1% methane+13.9% ethane (Gumusut-Kakap gas). The thickness and distribution of the gas hydrate stability zone (GHSZ) for Structure II hydrates were calculated using statistical thermodynamic methods. The results indicate that the thickness of the GHSZ in the SCS varies from 0 to 800 m. In the continental slope area, most of the thickness of the GHSZ are less than 500 m. In contrast, in localized areas such as the Manila Trench, the southwestern Nansha Trough, the South Palawan Basin, and the Luzon Strait, the thickness of the GHSZ exceeds 500 m. The new estimates of the GHSZ thickness for methane hydrates, 96% methane plus 4% ethane, and Gumusut-Kakap gas are 203 m, 219 m, and 254 m, respectively. Based on the volumetric method, the corresponding resource volumes are 82.65 Gt (115.43×1012 m³), 93.11 Gt (130.04×1012 m³), and 111.29 Gt (155.43×1012 m³) using the gas expansions of 155, 162 and 160, respectively. On this basis we calculated the incremental hydrate resource using the GHSZ thickness difference. The incremental resource volumes for the two Structure II hydrates are 10.46 Gt (14.61×1012 m³) for the 96% methane+4% ethane composition, representing an increase of approximately 13%, and 18.18 Gt (25.39×1012 m³) for the Gumusut - Kakap gas composition, representing an increase of approximately 22%. This study recalculates the natural gas hydrate resources in the South China Sea and can be used to assess global Structure II hydrate resources.
How to cite: Liu, Z. and Qian, J.: Gas hydrate potential of heavier order hydrocarbons in the South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17215, https://doi.org/10.5194/egusphere-egu25-17215, 2025.