Abstract

Gas hydrates from the continental margin settings are mostly confined to continental slopes. The free gas occurring below the gas hydrate laden sediments play a crucial role in the submarine slope failures and can potentially trigger the submarine landslides. The present study is carried out to investigate such a scenario in the shale dominated Krishna–Godavari (KG) basin having proven gas hydrate deposits. Shale reservoirs are less permeable compared to sandstone reservoirs and as such, the free gas that is locked in the pore spaces of shales would eventually create hydro fractures or faults to escape from the pore spaces. This overpressure from the gas zone will find a pathway to reach the shallower depths. In the present study, two faults are identified of which, one is acting as a potential pathway for overpressures to travel through it, while the other is found to be critically pressurized due to the gas zone below it. The calculated gas column height is ~51 m and any further increase in the gas column height would create a fault slip and cause the mechanical failure of the sediments, creating another potential pathway. We infer that these faults are acting as a migration pathway in our study area and the advection of fluid/gas from the gas zone via the pathway might have played a major role in creating a slope break above the fault.

Research highlights

• Gas migration and role of free gas on slope stability.

• Seismic attributes for characterization of free gas zones and migration pathways

• Gas column height and critical gas pressure necessary to initiate fault activation.

• Active and passive faults and their role as migration pathways.

中文翻译：

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海底斜坡破坏中的天然气水合物/自由气体迁移途径：东印度洋边缘

摘要

来自大陆边缘环境的天然气水合物主要局限于大陆斜坡。含天然气水合物的沉积物下方产生的游离气体在海底斜坡破坏中起着至关重要的作用，并有可能触发海底滑坡。本研究旨在调查以页岩为主的克里希纳-戈达瓦里（KG）盆地中已证实有天然气水合物沉积的情况。与砂岩储层相比，页岩储层的渗透性较差，因此，锁定在页岩孔隙中的游离气体最终会形成水力压裂或断层，从孔隙中逸出。来自气层的超压将找到一条到达较浅深度的路径。在本研究中，确定了两个断层，一个断层是超压穿过它的潜在途径，同时发现另一个由于其下方的气体区域而处于临界加压状态。计算出的气柱高度为〜51 m，气柱高度的任何进一步增加都会产生断层滑动，并导致沉积物的机械故障，从而形成另一条潜在的路径。我们推断这些断层在我们的研究区域中起着迁移路径的作用，并且通过该路径从气层出来的流体/气体的平流可能在造成断层上方的斜坡折断中起了重要作用。

研究重点

• 气体运移和自由气体对边坡稳定性的作用。

• 表征自由气层和迁移路径的地震属性

• 启动故障激活所需的气柱高度和临界气体压力。

• 主动和被动断层及其作为迁移途径的作用。