Methane hydrates in Black Sea deep-sea fans : Characteristics, implications, and related geohazards
Methane hydrates in Black Sea deep-sea fans : Characteristics, implications, and related geohazards
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发表时间：
2017-11
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通讯作者：
Timo Zander
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作者：
Timo Zander
本论文的重点是两个天然气水合物轴承研究地点在黑海。这些地点位于多瑙河和东库班深海扇复合体附近。通过使用各种地球物理方法，包括二维和三维地震，侧扫声纳，沉积物回声测深仪方法，以及地球化学分析和岩土建模，三个案例研究进行了调查。在第一个案例研究中，异常多个海底模拟反射（BSR）进行了调查，这发生在一个埋藏的渠道堤坝系统的多瑙河深海扇的堤坝。这些海底反射带可能是由黑海不同湖沼期的压力和温度变化引起的古海底反射带。BSR在地震数据中仍然可见，因为游离气可能仍然存在于其下方。由于游离气体只能通过扩散进行运输，因此大部分游离气体仍被困在细粒堤坝沉积物中，因此在气体水合物分解后仅释放少量气体。第二个案例研究的重点是一个潜在的浅层天然气水合物储层，这是在天然气水合物作为一种能源资源的开采方面的利益。为了确定假设的水合物储层天然气开采是否会导致开采区附近海底斜坡沿着发生边坡破坏，进行了斜坡稳定性分析。由于储层压实而引起的海底下沉可能不会降低附近斜坡的稳定性。因此，自然发生的边坡破坏比天然气水合物生产引发的滑坡更容易发生。第三个案例研究的重点是位于黑海东北部Don Kuban深海扇的刻赤渗漏点。渗漏点位于GHSZ内，水深约900 m。这三个渗漏点中的每一个都在渗漏圆顶下面拥有自己的气袋。生物源甲烷的传输主要以气泡的形式沿沿着狭窄的管道通过GHSZ。
This thesis focusses on two gas-hydrate-bearing study sites in the Black Sea. These sites are located in the vicinity of the Danube and Don-Kuban deep-sea fan complexes. By using a variety of geophysical methods, including 2D and 3D seismics, sidescan sonar, and sediment echosounder methods, as well as geochemical analysis and geotechnical modeling, three case studies were investigated. In the first case study, anomalous multiple bottom simulating reflectors (BSRs) were investigated, which occur in the levees of a buried channel-levee system of the Danube deep-sea fan. The BSRs are likely paleo-BSRs caused by a change in pressure and temperature conditions during different limnic phases of the Black Sea. The BSRs remain visible in seismic data because free gas is likely still present beneath them. As the free gas can only be transported by diffusion, it largely remains trapped within the fine-grained levee deposits, and therefore only small amounts of gas are released after gas hydrate dissociation. The second case study focusses on a potential shallow gas hydrate reservoir that is of interest in terms of exploitation of gas hydrates as an energy resource. To determine whether a hypothetical gas production out of the hydrate reservoir induces slope failures along the seabed slopes near the production area, a slope stability analysis was carried out. Seafloor subsidence due to reservoir compaction likely does not reduce the stability of the nearby slope. Consequently, naturally occurring slope failures are more likely to occur than landslides triggered by gas hydrate production. The third case study focuses on the Kerch seep site located in the Don Kuban deep-sea fan in the northeastern Black Sea. The seep site is located within the GHSZ in about 900 m water depth. Each of the three seeps hosts its own gas pocket underneath the seep domes. The transport of biogenic methane predominantly occurs in the form of gas bubbles along narrow pipes through the GHSZ.