Gas hydrate quantification at a pockmark offshore Norway from joint effective medium modelling of resistivity and seismic velocity
Gas hydrate quantification at a pockmark offshore Norway from joint effective medium modelling of resistivity and seismic velocity
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DOI：
10.1016/j.marpetgeo.2019.104151
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发表时间：
2017-06
影响因子：
4.2
通讯作者：
Eric Attias;Kelvin Amalokwu;M. Watts;I. Falcon‐Suarez;L. North;G. Hu;A. Best;K. Weitemeyer;T. Minshull
中科院分区：
文献类型：
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作者：
Eric Attias;Kelvin Amalokwu;M. Watts;I. Falcon‐Suarez;L. North;G. Hu;A. Best;K. Weitemeyer;T. Minshull
大陆边缘天然气水合物沉积物的甲烷排放可能会在局部和区域范围内改变海洋环境的生物地球物理特性。天然气水合物矿床的饱和度通常使用在感兴趣地点远程或现场测量的弹性或电特性来计算。在这里，我们结合了在挪威近海 Nyegga 地区获得的受控源电磁 (CSEM)、地震和沉积物岩心数据，采用联合弹性电方法来量化 CNE03 麻点内发现的海洋天然气水合物。对两个沉积物岩心的多尺度分析揭示了 CNE03 麻点与位于 CNE03 西北约 150 m 的参考地点之间的显着差异。在收集的 CNE03 沉积物中观察到气体水合物和化学合成双壳类。 CNE03沉积物岩心中测得的地震速度和电阻率分别与地震和CSEM遥感数据集得出的纵波速度（VP）和电阻率值一致。随着 CNE03 管状结构内深度的增加，V P 逐渐增加（约 1.75-1.9 km/s），而电阻率异常仍保持在约 3 Ω m。使用联合弹电有效介质模型对同位地震和 CSEM 数据进行联合解释表明，对于 0.55-0.65 的孔隙度范围，CNE03 水合物稳定区内的天然气水合物饱和度随深度变化，在 20% 至 48% 之间。在孔隙度为 0.6 时，CNE03 内的水合物饱和度在约 23% 至 37% 之间变化，而加权平均饱和度为约 30%。我们的结果表明，通过联合弹性-电有效介质建模耦合纵波速度和 CSEM 电阻率数据，可以实现良好约束的天然气水合物定量。本研究中应用的方法可用作量化各种海洋沉积物中水合物的框架。
Methane emissions from gas hydrate deposits along continental margins may alter the biogeophysical properties of marine environments, both on local and regional scales. The saturation of a gas hydrate deposit is commonly calculated using the elastic or electrical properties measured remotely or in-situ at the site of interest. Here, we used a combination of controlled-source electromagnetic (CSEM), seismic and sediment core data obtained in the Nyegga region, offshore Norway, in a joint elastic-electrical approach to quantify marine gas hydrates found within the CNE03 pockmark. Multiscale analysis of two sediment cores reveals significant differences between the CNE03 pockmark and a reference site located approximately 150 m northwest of CNE03. Gas hydrates and chemosynthetic bivalves were observed in the CNE03 sediments collected. The seismic velocity and electrical resistivity measured in the CNE03 sediment core are consistent with the P-wave velocity (V P) and resistivity values derived from seismic and CSEM remote sensing datasets, respectively. The V P gradually increases (~ 1.75–1.9 km/s) with depth within the CNE03 pipe-like structure, whereas the resistivity anomaly remains~ 3 Ω m. A joint interpretation of the collocated seismic and CSEM data using a joint elastic-electrical effective medium model suggests that for the porosity range 0.55–0.65, the gas hydrate saturation within the CNE03 hydrate stability zone varies with depth between~ 20 and 48%. At 0.6 porosity, the hydrate saturation within CNE03 varies between~ 23 and 37%, whereas the weighted mean saturation is~ 30%. Our results demonstrate that a well-constrained gas hydrate quantification can be accomplished by coupling P-wave velocity and CSEM resistivity data through joint elastic-electrical effective medium modelling. The approach applied in this study can be used as a framework to quantify hydrate in various marine sediments.