南海北部神狐海域沉积物颗粒对天然气水合物聚集的主要影响
摘要
An important parameter is the saturation of gas hydrate within the sediment pore for evaluating its impact on energy, climate and environment. So it is significant of understanding which factors affecting the saturation of gas hydrates. There is a good relationship between the gas hdyrate saturation and the sediment granulometric charateristics by previous investigations. Gas hydrates with high saturation are retrieved usually from the turbidite, sand layers, which formations are of coarse particles and relatively larger pore space. But the knowledge up to today is still on the level of simple statistic and qualitative. In this paper, the samples from site SH3, Shenhu, South China Sea, are undergone the grain size & specific surface area (SSA) measurements. Then a mathematical model is built to depict that the SSA characterizing the pore size and the change of gas hydrates phase equilibruim condition. Thus, the scientific question, how the sediment grains affecting the gas hydrates saturation, can be analysed and discussed quantitatively. The experiment results show that, the sediment layers which are not bearing gas hydrates, consist of clay(<4 μm), silt (4-63 μm) and the very fine sand (63-125 μm). The major components of silt (4-63 μm) contribute to 80%, while the content of clay is almost 20%. The gas hydrate occurrence zone (GHOZ) is constrained by the fine silt layers (silt content>60%). The sediment layer of GHOZ contains the most coarsest grains (>125 μm, content<10%) of sand except for the very fine sand (63-125 μm), while the layers up & below GHOZ do not contain the coarsest parts. The gas hydrate saturation does not depend simply on the sand (>63 μm) content. There is a more better correlation between hydrate saturation and the sand content except for the very fine sand (>125 μm). This is by now the most elaborate report of the relationship between gas hydrates saturation and sediment grain size characterization. The SSA of sedi