Resistivity image beneath an area of active methane seeps in the west Svalbard continental slope
Resistivity image beneath an area of active methane seeps in the west Svalbard continental slope
复制标题
DOI：
10.1093/gji/ggw330
复制
发表时间：
2016-11
影响因子：
2.8
通讯作者：
Bedanta K. Goswami;K. Weitemeyer;T. Minshull;M. Sinha;G. Westbrook;H. Marín‐Moreno
中科院分区：
文献类型：
--
作者：
Bedanta K. Goswami;K. Weitemeyer;T. Minshull;M. Sinha;G. Westbrook;H. Marín‐Moreno
北极大陆边缘以甲烷水合物的形式含有大量甲烷。西斯瓦尔巴群岛陆坡是一个据报道在水合物稳定带向陆地边界附近有活动甲烷渗漏的地区。在水深大于600m的地震反射资料上，存在模拟海底反射层(BSR)，这表明该地区天然气水合物下存在游离气。由海洋可控源电磁(CSEM)资料获得的电阻率比周围水饱和沉积物的电阻率更高，为探测浅层水合物和天然气的地震方法提供了有用的补充。我们在斯瓦尔巴群岛西部陆坡获得了两条CSEM线，它们从大陆架边缘(水深250m)延伸到约800m的水深。在BSR上方观察到的高电阻率(5-12Ωm)支持在600m以上的水深存在天然气水合物。390-600m水深的高电阻率(3-4Ωm)也表明在陆坡的天然气水合物稳定带内可能存在水合物。此外，GHSZ向陆地的高电阻率(4-8Ωm)与地震数据中报告的高幅度反射层和低速度相吻合，这表明可能存在游离气。利用连通性方程估算的孔隙空间饱和度表明，下坡沉积物中的水合物含量为20%-50%，上坡沉积物中的水合物含量不到12%。GHSZ下方的游离气区域(含气饱和度为10-20%)与大陆架边缘的高含气饱和区(含气饱和度为10-45%)相连，大部分渗漏都在这里观察到。这一证据支持GHSZ下方存在向大陆架横向迁移的游离气。
The Arctic continental margin contains large amounts of methane in the form of methane hydrates. The west Svalbard continental slope is an area where active methane seeps have been reported near the landward limit of the hydrate stability zone. The presence of bottom simulating reflectors (BSRs) on seismic reflection data in water depths greater than 600 m suggests the presence of free gas beneath gas hydrates in the area. Resistivity obtained from marine controlled source electromagnetic (CSEM) data provides a useful complement to seismic methods for detecting shallow hydrate and gas as they are more resistive than surrounding water saturated sediments. We acquired two CSEM lines in the west Svalbard continental slope, extending from the edge of the continental shelf (250 m water depth) to water depths of around 800 m. High resistivities (5–12 Ωm) observed above the BSR support the presence of gas hydrate in water depths greater than 600 m. High resistivities (3–4 Ωm) at 390–600 m water depth also suggest possible hydrate occurrence within the gas hydrate stability zone (GHSZ) of the continental slope. In addition, high resistivities (4–8 Ωm) landward of the GHSZ are coincident with high-amplitude reflectors and low velocities reported in seismic data that indicate the likely presence of free gas. Pore space saturation estimates using a connectivity equation suggest 20–50 per cent hydrate within the lower slope sediments and less than 12 per cent within the upper slope sediments. A free gas zone beneath the GHSZ (10–20 per cent gas saturation) is connected to the high free gas saturated (10–45 per cent) area at the edge of the continental shelf, where most of the seeps are observed. This evidence supports the presence of lateral free gas migration beneath the GHSZ towards the continental shelf.