Characterization of natural gas hydrate recovered from Pearl River Mouth basin in South China Sea

Many researchers have estimated the thickness of the gas hydrate stability zone (GHSZ) and amount of gas hydrate at different areas in the South China Sea (SCS) using varying methods, but few have reported calculations for the whole of the SCS. In this paper, Milkov and Sassen's model is used to calculate the thickness of the GHSZ in the SCS. In addition, an estimation of the amount of gas hydrate and discussed in terms of gas composition and the effects of water depth. Average thicknesses for the GHSZ in the SCS are estimated to be similar to 440 m, similar to 477 m and similar to 553 m based on the relationship between GHSZ thickness and water depth established in this study for 3 kinds of gas hydrates with gas composition containing 100% methane, 96% methane, and 90% methane, respectively. Then, by assuming that gas hydrates are distributed in half of the continental slope area of the SCS, and that the gas hydrate saturation is 1.2% of sediment volume, the amounts of gas hydrate are estimated to be similar to 3.2 x 10(12) m(3), similar to 3.4 x 10(12) m(3), similar to 4.0 x 10(12) m(3), and the volumes of hydrate-bound gases are similar to 5.2 x 10(14) m(3), similar to 5.6 x 10(14) m(3), similar to 6.5 x 10(14) m(3) for the 3 kinds of gas hydrates above, respectively. The results above show that water depth and gas composition are important factors affecting the thickness of the GHSZ in which the thickness of the GHSZ increases with water depth and decreases with the volume of methane, and that the gas hydrate may be a potential energy source in SCS.

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Mapping the Thickness of the Gas Hydrate Stability Zone in the South China Sea

The Shenhu area is one of the promise target areas for marine gas hydrate exploration in the northern margin of the South China Sea. Pore water samples were collected from two piston cores (8.75 and 8.52 m) in site HS-A and site HS-B in the Shenhu area, and their major anion and cation contents and trace element contents have been analyzed in this study. Cl− concentrations in pore waters are similar to the seawater value and no systematic change along depth profiles has been found for the Cl− content in both sites. In site HS-A, the SO42− contents show a limited range in pore waters from 0 to 3 m depths, but a dramatic decrease is documented in depth below 3 m. Other elements such as Ca2+, Mg2+ and Sr2+ show similar variation patterns as the SO42−, i.e., no variation in 0–3 m, but large decrease in depth below 3 m. In site HS-B, both the SO4 and Ca2+, Mg2+ and Sr2+ display a decrease pattern along the depth profile, but in 0–3 m the variation is less significant than those in depth below 3 m. In both sites HS-A and HS-B, I contents show a dramatic increase along depth profiles. Calculations show that the SMI depths are very shallow (10 and 11 m) in both sites, and the sulfate flux and I flux are very high. These geochemical characteristics and anomalies at Shenhu are quite similar to those found in other gas hydrate locations in the world, and a genetic link is suggested to be related to the gas hydrate occurrence at depths in the study area. In summary, we suggest that combined geochemical parameters in shallow sediment pore waters are useful indicators to indicate the gas hydrate occurrence at depths.

Geochemical characteristics of pore water in shallow sediments from Shenhu area of South China Sea and their significance for gas hydrate occurrence

Shenhu 区域是为在华南海的北边缘的海洋的煤气的水合物探索的诺言目标区域之一。毛孔水样品在地点 HS 从二个活塞核心(875 和 852 m ) 被收集 -- 在 Shenhu 区域的 A 和地点 HS-B，和他们的主要阴离子和阳离子内容和踪迹元素满足在这研究被分析了。Cl？毛孔水里的集中类似于海水价值，沿着深度侧面的系统的变化都没被作出对有利的裁决 Cl 吗？在两个地点的内容。在地点 HS -- 一， SO42？内容证明从 0 ～ 3 m 深度的毛孔水里的一个有限范围，而是戏剧的减少在 3 m 下面深入地被记录。象 Ca2+ ， Mg2+ 和 Sr2+ 那样的另外的元素作为 SO42 显示出类似的变化模式 ? ，即，在 03 m 的没有变化，而是深入地在 3 m 下面的大减少。在地点 HS-B， SO4 和 Ca2+ ， Mg2+ 和 Sr2+ 沿着深度侧面显示一个减少模式，但是在 03 m，变化是不比深入地在 3 m 下面的那些重要的。在两地点 HS -- A 和 HS-B，我满足表演沿着深度侧面的戏剧的增加。在地点，和硫酸盐流动的 SMI 深度是很浅的计算表演(10 和 11 m ) 并且我流动很高。在 Shenhu 的这些 geochemical 特征和异例相当类似于在世界上在另外的煤气的水合物地点发现的那些，并且一个基因连接被建议与在在学习区域的深度的煤气的水合物出现有关。在摘要，我们建议浅沉积毛孔水里的联合 geochemical 参数是有用指示物在深度显示煤气的水合物出现。

BSRs, estimated heat flow, hydrate-related gas volume and their implications for methane seepage and gas hydrate in the Dongsha region, northern South China Sea

The geological and tectonic characteristics for generating gas hydrate in the Dongsha continental slope of the South China Sea were analyzedIt is suggested that tectonics and sedimentation play the important roles in the generation of methane hydrateThe range of occurrence of bottom simulating reflector(BSR) in the Dongsha continental slope of the South China Sea was mapped by means of some high-resolution seismic dataThe BSR clearly appeared on the seismic profiles of the lower slope,whereas it was few discovered in the upper slopeThe BSR was mainly distributed in the transition zone between the continental crust and oceanic crust southwestward the Dongsha IslandsThe background of the region was characterized by the passive continental marginThe BSR were distributed in the range of debris flow and turbidity sedimentationThis means that debris and turbidity are sufficiently high to allow the vertical transport of large volumes of methane and to form the gas hydrateThe occurrence of BSR was resulted from anomaly overpressure fluid including gas and water,because of the rapid sedimentary rate revealed by ODP drilling and piston cores during the Late CenozoicThe high heat flow values indicate that the active tectonics and deep crust fluid in the region benefit to the generation of gas hydrateOtherwise,few BSR and gas hydrate occurred in the upper slope,because of the thin sedimentary layers and serious tectonic erosion

Wu Shi

Papers

Geological constraint on the distribution of gas hydrate in the Dongsha continental slope of South China Sea