Seismic imaging of gas conduits beneath seafloor seep sites in a shallow marine gas hydrate province, Hikurangi Margin, New Zealand
Seismic imaging of gas conduits beneath seafloor seep sites in a shallow marine gas hydrate province, Hikurangi Margin, New Zealand
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DOI：
10.1016/j.margeo.2009.03.007
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发表时间：
2010-07-15
期刊：
影响因子：
2.9
通讯作者：
Greinert, Jens
中科院分区：
文献类型：
--
作者：
Crutchley, Gareth J.;Pecher, Ingo A.;Greinert, Jens
我们介绍了最近从岩石花园获得的高分辨率地震数据和较早的较低分辨率地震数据，岩石花园是新西兰Hikurangi边缘的一个浅海天然气水合物省。地震数据揭示了管道系统，这些管道系统向三个一般地点供应天然气，这些地点在岩石花园海底发现了渗漏：“LM3”站点(包括LM3和LM3-A)、“Weka”站点(包括Weka-A、Weka-B和Weka-C)和“Faure”站点(包括Faure-A、Faure-B和Rock Garden Knoll)。在LM3地点，地震数据显示天然气从海底拟反射(BSR)之下，通过天然气水合物稳定带(GHSZ)运移到两个独立的海底渗漏(LM3和LM3-A)。天然气在LM3渗漏下方通过GHSZ更深的部分运移似乎受到主要逆冲断层上盘断层的影响。在离海底更近的地方，主要的迁徙路径似乎占据了垂直烟囱。在韦卡遗址，在山脊的中央部分，地震数据显示BSR非常浅。在其中一个Weka渗漏位置(Weka-A)的出口点观察到BSR与海底的明显会聚。向该渗漏供应的天然气预计将集中在由上覆天然气水合物引起的BGHS渗透率对比的底部。Faure地点与Faure-A显著的弧形坍塌特征有关，从浅层BSR向海底延伸的高幅度反射被解释为利用相对高渗透率沉积层的首选天然气运移路径。在Faure-B，我们解释天然气沿BGHS底部向渗漏输送-与岩石花园Knoll的Weka-A遗址解释的相同情景，天然气占据GHSZ内的浅层沉积物，并被解释为沿相对高渗透率的层向上迁移到海底渗漏区。我们预测，由于隆起和山脊的弯曲伸展，断裂作用可能是形成流体管道的重要机制，该管道将BGHS之下的游离气储集层与岩石花园Knoll之下的浅层天然气聚集在一起。从更区域性的角度来看，Rock Garden下的大部分天然气集中在西北向倾斜的组构上，可能与边缘俯冲相关的变形有关(C)2009 Elsevier B.V.
We present recently-acquired high-resolution seismic data and older lower-resolution seismic data from Rock Garden, a shallow marine gas hydrate province on New Zealand's Hikurangi Margin The seismic data reveal plumbing systems that supply gas to three general sites where seeps have been observed on the Rock Garden seafloor the 'LM3' sites (including LM3 and LM3-A), the 'Weka' sites (including Weka-A, Weka-B, and Weka-C), and the 'Faure' sites (including Faure-A, Faure-B, and Rock Garden Knoll). At the LM3 sites, seismic data reveal gas migration from beneath the bottom simulating reflection (BSR), through the gas hydrate stability zone (GHSZ), to two separate seafloor seeps (LM3 and LM3-A) Gas migration through the deeper parts of GHSZ below the LM3 seeps appears to be influenced by faulting in the hanging wall of a major thrust fault. Closer to the seafloor, the dominant migration pathways appear to occupy vertical chimneys. At the Weka sites, on the central part of the ridge, seismic data reveal a very shallow BSR. A distinct convergence of the BSR with the seafloor is observed at the exit point of one of the Weka seep locations (Weka-A) Gas supply to this seep is predicted to be focused along the underside of a permeability contrast at the BGHS caused by overlying gas hydrates The Faure sites are associated with a prominent arcuate slump feature At Faure-A, high-amplitude reflections, extending from a shallow BSR towards the seafloor, are interpreted as preferred gas migration pathways that exploit relatively-high-permeability sedimentary layers. At Faure-B, we Interpret gas migration to be channelled to the seep along the underside of the BGHS - the same scenario interpreted for the Weka-A site At Rock Garden Knoll, gas occupies shallow sediments within the GHSZ, and is interpreted to migrate up-dip along relatively-high-permeability layers to the area of seafloor seepage. We predict that faulting, in response to uplift and flexural extension of the ridge, may be an important mechanism in creating fluid flow conduits that link the reservoir of free gas beneath the BGHS with the shallow accumulations of gas imaged beneath Rock Garden Knoll From a more regional perspective, much of the gas beneath Rock Garden is focused along a northwest-dipping fabric, probably associated with subduction-related deformation of the margin (C) 2009 Elsevier B.V. All rights reserved