Seismic evidence of shallow gas from Lake Van, eastern Turkey
Seismic evidence of shallow gas from Lake Van, eastern Turkey
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DOI：
10.1016/j.marpetgeo.2013.08.017
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发表时间：
2013-12
影响因子：
4.2
通讯作者：
D. Cukur;S. Krastel;Y. Tomonaga;M. Çağatay;A. Meydan
中科院分区：
文献类型：
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作者：
D. Cukur;S. Krastel;Y. Tomonaga;M. Çağatay;A. Meydan
对凡湖（土耳其东部）的多道地震反射和线性调频数据的分析揭示了各种浅层气体指标，包括地震烟囱、增强反射、亮点、泥火山、麻点和声学消隐。增强的反射最为显着，表明存在游离气体，在 200 多个地点观察到。它们的特点是反射幅度非常高，并且发生在深部和浅部沉积部分。一些增强的反射伴随着非常微妙的海底表情，例如土丘，这可能表明活跃的通风活动。在大部分调查区域都观察到了地震烟囱或振幅消隐的柱状区。研究区域的地震烟囱与任何可能充当深层流体运移通道的已知断层无关。这表明在范湖沉积物中观察到的结构允许优先排放气体，这可能是大部分生物来源的气体。在湖的东部可以看到以透明或混沌地震相为特征的声波消隐。声波消隐的湖边边缘与 100 m 水深等高线基本一致，表明（过去）静水压力的变化可能是造成这些异常分布的原因。一些地方出现了类似土丘的特征，被解释为泥火山。这些特征的存在可能表明活性气体排放。在许多地方还可以看到非常强的振幅异常或具有负极性的亮点，表明充满气体的区域。仅在研究区域的东北部观察到麻点。研究区域很少出现麻点可能是由于湖泊沉积物的渗透性较高，或者是由于缺乏产生这种特征所需的临界气体质量的基质/储层。浊积岩、火山灰层和三角洲沉积物有可能为沉积物充当气藏提供理想的条件。
Analysis of multi-channel seismic reflection and chirp data from Lake Van (eastern Turkey) reveals various shallow gas indicators including seismic chimneys, enhanced reflections, bright spots, mud volcanoes, pockmarks, and acoustic blanking. The enhanced reflections, suggesting the presence of free gas, are most dominant and observed at more than 200 locations. They are characterized by very-high amplitude reflections and occur in both deep and shallow sedimentary sections. Some enhanced reflections are accompanied by very subtle seafloor expressions such as mounds, which may suggest active venting activity. Seismic chimneys or columnar zones of amplitude blanking have been observed in much of the surveyed area. Seismic chimneys in the study area cannot be associated with any known faults that would act as migration pathways for deep fluids. This suggests that the observed structures in Lake Van sediments allow the preferential emission of gases which might be for a large share of biogenic origin. The acoustic blanking, characterized by transparent or chaotic seismic facies, is seen in the eastern part of the lake. The lakeward edge of the acoustic blanking largely coincides with the 100 m water depth contour, indicating that (past) changes of the hydrostatic pressure may be responsible for the distribution of these anomalies. Mound-like features, interpreted as mud volcanoes, occur in a few locations. The presence of these features may suggest active gas emission. Very strong amplitude anomalies or bright spots with negative polarity, indicating gas-charged zones, are also seen in a number of locations. Pockmarks are observed only in the northeastern part of the study area. The scarce occurrence of pockmarks in the study area might be ascribed to a higher permeability of the lake sediments or to the absence of the substrate/reservoir providing the critical mass of gases necessary to produce such features. Turbidites, tephra layers, and deltaic deposits have the potential to provide ideal conditions to allow the sediments to act as a gas reservoir.