Numerical investigation on methane hydrate accumulation in Shenhu Area, northern continental slope of South China Sea

摘要

The hydrate deposits in Shenhu Area on northern continental slope of the South China Sea is regarded as one of the promising targets for gas hydrate exploration and exploitation in China. The hydrates concentrate at base of gas hydrate stability zone (GHSZ) with a peak saturation of 48%. However, the formation mechanism and controlling factors of the hydrates remain unclear. Previous studies suggested that sedimentation flux and water flux are two fundamental parameters controlling hydrate accumulation. Here, we have applied a one-dimensional dynamic model to characterize the hydrate evolution pattern at a drilling site of SH2 in Shenhu Area. The hydrate saturations modeled at current sedimentation rate and water flow rate were much different from the values approved. Some perturbations of the two parameters seemed to be useless to improve the modeling. The big finding was that the modeled result basically matched the saturation values at initial hydrate saturations of 20-22%. The results indicated that massive gas hydrates formed in the early fractured sediment in Shenhu Area, the sediment evolved by inheriting the "ancient" hydrate and lasted for ~ 1.5 Myrs before present and produces the current hydrate feature. The modeling implies that resource potential of Shenhu hydrate has been decreasing.