Hydrate‐filled Fracture Formation at Keathley Canyon 151, Gulf of Mexico, and Implications for Non‐vent Sites
Hydrate‐filled Fracture Formation at Keathley Canyon 151, Gulf of Mexico, and Implications for Non‐vent Sites
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DOI：
10.1029/2019gc008637
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发表时间：
2019-11
期刊：
影响因子：
3.7
通讯作者：
E. Oti;A. Cook;S. Welch;J. Sheets;D. Crandall;K. Rose;H. Daigle
中科院分区：
文献类型：
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作者：
E. Oti;A. Cook;S. Welch;J. Sheets;D. Crandall;K. Rose;H. Daigle
近垂直的水合物填充的裂缝在海底下的海洋泥浆中被发现，在平流甲烷喷口和没有明显甲烷和流体平流的地点（非喷口地点）。在非喷口地区，将甲烷输送到裂缝并控制水合物填充裂缝形成的机制尚未得到很好的理解。然而，这些机制是重要的建立，因为大多数地球的天然气水合物可能是在海洋泥浆系统约束。在此，我们通过检查2005年天然气水合物联合工业项目在美国北方墨西哥湾Keathley峡谷151号采集的常规岩心中先前含有水合物的裂缝，重点了解水合物的起源以及裂缝如何在非喷口部位形成。我们结合了来自测井记录、沉积物岩心和科学小组成果的联合收割机信息，并添加了档案切片的新X射线计算机断层扫描和岩心样品的扫描电子显微镜，以开发一个概念模型。我们认为，本地产生的微生物甲烷通过扩散从海洋泥浆中的小孔进入具有较大孔径的生物矿化洞穴，这一过程称为短程迁移。一旦甲烷扩散到洞穴中，并且溶解的甲烷浓度超过溶解度阈值，则在洞穴中形成Hyphilis。当水合物填充洞穴时，来自额外水合物生长的隆起在洞穴边缘上施加应力，使裂缝扩大，并产生额外的空隙空间，甲烷可以在其中扩散并继续形成水合物。裂缝沿最大主应力方向缓慢扩展。
Near‐vertical hydrate‐filled fractures are found in subseafloor marine muds, at both advective methane vent sites and at sites without obvious methane and fluid advection (non‐vent sites). At non‐vent sites, the mechanisms that transport methane to the fractures and control how hydrate‐filled fractures form are not well understood. However, these mechanisms are important to establish, as most of Earth's natural gas hydrate is likely bound in marine mud systems. Herein, we focus on understanding the origin of hydrate and how fracture form at non‐vent sites by examining previously hydrate‐bearing fractures in conventional cores taken from Keathley Canyon 151, U.S. northern Gulf of Mexico, drilled by the Gas Hydrate Joint Industry Project in 2005. We combine information from well logs, sediment cores, and science party results and add new X‐ray computed tomography of archival sections and scanning electron microcopy of core samples to develop a conceptual model. We propose that locally generated microbial methane is transported via diffusion from small pores in marine mud into biomineralized burrows with larger pore size in a process called short‐range migration. Hydrate forms in burrows once the methane diffuses into them and the dissolved methane concentration exceeds the solubility threshold. When hydrate fills a burrow, heave from additional hydrate growth places stress on the burrow edges, expands the fracture, and creates additional void space in which methane can diffuse and continue forming hydrate. Fractures slowly propagate in the direction of maximum principal stress.