3D thermobaric modelling of the gas hydrate stability zone onshore central Spitsbergen, Arctic Norway
3D thermobaric modelling of the gas hydrate stability zone onshore central Spitsbergen, Arctic Norway
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DOI：
10.1016/j.marpetgeo.2018.10.050
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发表时间：
2019-02
影响因子：
4.2
通讯作者：
P. Betlem;Kim Senger;Andy Hodson
中科院分区：
文献类型：
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作者：
P. Betlem;Kim Senger;Andy Hodson
陆上天然气水合物（NGHs）的分离可能导致甲烷直接释放到大气中，特别是在斯瓦尔巴群岛等北极地区，在那里，气候变暖加剧有能力促进甲烷在永久冻土和冰川冰腐烂后迅速逃逸到大气中。在这里，我们首次对斯匹次卑尔根中部的天然气水合物稳定带（GHSZ）进行了评估，该稳定带是斯瓦尔巴群岛气候敏感的一部分，热压条件似乎有利于陆上天然气水合物的形成。我们开发了一种结合区域约束的温度、压力和相边界（93%甲烷，7%乙烷，35 ppt盐度）的三维参数化方法来定义GHSZ。这导致了覆盖74.8%研究区域的厚达650 m（平均308 m）的GHSZ，在气候较冷的东部地区显著增厚。对基本情况参数进行了扰动，以量化GHSZ对整个研究区域环境条件变化的敏感性。结果表明，当乙烷含量（增加到20%）或区域孔隙水压力（增加到125%静水压力）增加时，GHSZ的变化最大。当地温梯度从33°C降低到26 °C km−1时，GHSZ也显著增加，但几乎完全被干气（100%甲烷）、更高的盐度（50 ppt）或暴露于相对于年平均气温的地表温度升高（例如2 °C）所抑制。除地温梯度主要影响下稳定边界外，大部分参数同时影响GHSZ上稳定边界和下稳定边界。鉴于斯瓦尔巴群岛拥有一个已探明的石油系统，我们得出的结论是，天然气水合物几乎肯定存在于斯瓦尔巴群岛陆上。
Dissociation of onshore natural gas hydrates (NGHs) could lead to the release of methane directly to the atmosphere, especially in Arctic regions such as Svalbard, where enhanced climate warming has the capacity to promote rapid methane evasion to the atmosphere following the decay of permafrost and glacier ice. Here we present the first assessment of the NGH stability zone (GHSZ) in central Spitsbergen, a climate-sensitive part of Svalbard where thermobaric conditions appear favourable for onshore NGH formation. We developed an approach incorporating regionally constrained 3-dimensional parameterisation of temperature, pressure and phase boundary (93% methane, 7% ethane, 35 ppt salinity) to define the GHSZ. This resulted in an up to 650 m thick (mean: 308 m) GHSZ covering 74.8% of the study area, thickening significantly in the east where the climate is colder. Perturbation of the base case parameters was undertaken to quantify the sensitivity of the GHSZ to the variation in environmental conditions across the study area. We present 26 examples of these deterministic scenarios and show that the largest changes in the GHSZ were observed when either the ethane content (to 20%) or the regional pore water pressure (to 125% hydrostatic) were increased. The GHSZ also increased markedly when the geothermal gradient was reduced from 33 to 26 °C km−1, but was almost completely inhibited by a dry gas (100% methane), greater salinity (50 ppt), or exposure to an increase in surface temperatures relative to the mean annual air temperature (e.g., by 2 °C). Most parameters affected both the upper and the lower stability boundary of the GHSZ, with the exception of the geothermal gradient, which impacted primarily upon the latter. Given that Svalbard is host to a proven petroleum system, we conclude that NGHs almost certainly exist onshore Svalbard.