Methane Solubility in a Gas Hydrate Environment at the Shenhu Trial Production Area, Northern South China Sea

The Shenhu area in the northern South China Sea is a key region for gas hydrate exploration and trial production in China, where two successful trial production operations have been carried out. Using the approach established by [Davie, M. K. Mar. Geol. 2004, 203, 177–184] for predicting methane solubility in a marine setting, we determined the methane solubility profile at the SHSC-4 trial production site in the Shenhu area under in situ phase-equilibrium conditions. The calculated methane solubility at the base of the hydrate stability zone (HSZ) is 120.23 mM, decreasing exponentially to 58.02 mM toward the seafloor. This profile exhibits a relatively steep slope, comparable to that observed at site 889 on the Cascadia Margin, suggesting a significant loss of methane due to chemical diffusion. In combination with low total organic carbon content in the sediments, we infer that the methane supply in the Shenhu area is primarily of deep origin, and that in situ microbial methanogenesis is insufficient to sustain the local hydrate accumulation.