Abstract:

The development and existence of the gas hydrates are controlled prominently by the structural conditions. Several special structural units in the active or passive continental margins including accretionary wedge, mud volcano, mud diaper and seafloor slip  are favorable structures for the development and existence of gas hydrates. The investigation and research in the north slope of the South China Sea (SCS) suggest that the depression-upwelling faulted zone (DUFZ) is one of the important favorable structural circumstances for gas hydrates coming into being. Based on the comprehensive comparison, the temperature in the sediment is calculated from the relationship between the water depth and the seafloor temperature in the northern slope of the SCS, while the lithostatic pressure in the sediment is calculated from the relationship between the sediment depth and body density which was simulated in this paper. Furthermore, the P-T environment of the profile A which traverses the structure of DUFZ is analyzed in detail. The result shows that the free gas can always meet the favorable P-T environment and form gas hydrates when the gas transfers in the DUFZ because of the continuous variation of P-T environment in the structure, but it is not everywhere. The analysis of temperature and pressure in situ is necessary for the location of the gas hydrates.

Key words: hydrate, P-T environment, depression-upwelling faulted zone (DUFZ), the South China Sea