A joint electromagnetic and seismic study of an active pockmark within the hydrate stability field at the Vestnesa Ridge, West Svalbard margin
A joint electromagnetic and seismic study of an active pockmark within the hydrate stability field at the Vestnesa Ridge, West Svalbard margin
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DOI：
10.1002/2015jb012344
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发表时间：
2015-10-01
影响因子：
3.9
通讯作者：
Ker, Stephan
中科院分区：
文献类型：
--
作者：
Goswami, Bedanta K.;Weitemeyer, Karen A.;Ker, Stephan
我们获得了一致的海洋受控源电磁（CSEM），高分辨率地震反射和海底地震仪（OBS）数据在一个活跃的凹坑在顶部的南部的韦斯特内萨岭，估计流体成分内的底层流体迁移烟囱。合成模型研究表明，从CSEM数据获得的电阻率可以解决烟囱内的气体或水合物饱和度大于5%。在麻点下面和山脊侧面的地震反射数据成像的声烟囱被发现与高电阻率异常（+2-4米）有关。在天然气水合物稳定带（GHSZ）内还观察到高速异常（+0.3km/s）和GHSZ下伏的低速异常（-0.2km/s）。电阻率和速度异常的联合分析表明，孔隙饱和度高达52%的水合物与28%的游离气体，或高达73%的水合物与4%的游离气体，假设一个不均匀和均匀的流体分布，分别在麻点下方的烟囱。同样，我们估计高达30%的水合物与4%的游离气体或30%的水合物与2%的游离气体的GHSZ的孔隙空间内的中央烟囱外假设一个不均匀和均匀的流体分布，分别。在烟囱顶部的高水平的自由气体饱和度是一致的，从麻点的幕式气体排放。
We acquired coincident marine controlled source electromagnetic (CSEM), high-resolution seismic reflection and ocean-bottom seismometer (OBS) data over an active pockmark in the crest of the southern part of the Vestnesa Ridge, to estimate fluid composition within an underlying fluid-migration chimney. Synthetic model studies suggest resistivity obtained from CSEM data can resolve gas or hydrate saturation greater than 5% within the chimney. Acoustic chimneys imaged by seismic reflection data beneath the pockmark and on the ridge flanks were found to be associated with high-resistivity anomalies (+2-4m). High-velocity anomalies (+0.3km/s), within the gas-hydrate stability zone (GHSZ) and low-velocity anomalies (-0.2km/s) underlying the GHSZ, were also observed. Joint analysis of the resistivity and velocity anomaly indicates pore saturation of up to 52% hydrate with 28% free gas, or up to 73% hydrate with 4% free gas, within the chimney beneath the pockmark assuming a nonuniform and uniform fluid distribution, respectively. Similarly, we estimate up to 30% hydrate with 4% free gas or 30% hydrate with 2% free gas within the pore space of the GHSZ outside the central chimney assuming a nonuniform and uniform fluid distribution, respectively. High levels of free-gas saturation in the top part of the chimney are consistent with episodic gas venting from the pockmark.