Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard
Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard
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与斯瓦尔巴群岛西部近海后退的天然气水合物带相关的浅层气体逃逸特征的地震证据
DOI：
10.1029/2011jb009126
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发表时间：
2012
期刊：
影响因子：
3.4
通讯作者：
Sarkar S
中科院分区：
文献类型：
--
作者：
Sarkar S
活跃的天然气喷发发生在斯瓦尔巴群岛西部的最高大陆坡上，靠近目前甲烷水合物稳定性基准（BMHS）与Kongsfjorden和Isfjorden跨大陆架槽之间约400 m水深的海底相交处和上坡。通过对高分辨率二维叠前偏移地震反射剖面和多波束测深资料的综合分析，在扇间地区建立了一个模拟海底反射层（BSR），并对地下天然气的运移和聚集进行了分析。天然气渗漏主要发生在最近（1975-2008年）海底BMHS因底层水温上升1°C而退缩的区域。由于缺乏断层的地震证据，天然气渗漏的整体边缘平行排列与断层控制的天然气运移无关。没有证据表明在上斜坡的天然气火炬区附近存在BSR，但在预测的BMHS正下方存在许多气袋。虽然天然气渗漏的等值线趋势可能是BMHS和天然气水合物分解的向陆地界限后退的结果，但可能的水合物分解走廊内渗漏的分散分布以及预测的BMHS界限之外和陆架断裂附近的一组渗漏的发生表明了岩性异质性在集中天然气迁移中的作用。
Active gas venting occurs on the uppermost continental slope off west Svalbard, close to and upslope from the present‐day intersection of the base of methane hydrate stability (BMHS) with the seabed in about 400 m water depth in the inter‐fan region between the Kongsfjorden and Isfjorden cross‐shelf troughs. From an integrated analysis of high‐resolution, two‐dimensional, pre‐stack migrated seismic reflection profiles and multibeam bathymetric data, we map out a bottom simulating reflector (BSR) in the inter‐fan region and analyze the subsurface gas migration and accumulation. Gas seeps mostly occur in the zone from which the BMHS at the seabed has retreated over the recent past (1975–2008) as a consequence of a bottom water temperature rise of 1°C. The overall margin‐parallel alignment of the gas seeps is not related to fault‐controlled gas migration, as seismic evidence of faults is absent. There is no evidence for a BSR close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted BMHS. While the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the BMHS and gas hydrate dissociation, the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted BMHS limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration.