Shallow gas and gas hydrate occurrences on the northwest Greenland shelf margin
Shallow gas and gas hydrate occurrences on the northwest Greenland shelf margin
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DOI：
10.1016/j.margeo.2020.106382
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发表时间：
2021-02-01
期刊：
影响因子：
2.9
通讯作者：
Knutz, Paul C.
中科院分区：
文献类型：
--
作者：
Cox, David R.;Huuse, Mads;Knutz, Paul C.
广泛的三维地震数据集被用来调查当代碳氢化合物分布和历史流体迁移在梅尔维尔湾近海西北格陵兰岛，提供了第一个库存的浅层天然气和天然气水合物沿着这部分格陵兰岛边缘。浅层气异常在地震特征上各不相同，可分为孤立的浅层气、天然气水合物稳定带底部的游离气、含气冰川斜坡和大型块状运移存款气藏四类。通过识别标志着GHSZ基底的不连续海底模拟反射层（B SR），在537 km（2）的区域内识别出了天然气水合物矿床。BSR已被用于估计整个GHSZ的地热梯度为49 ℃/km，热流为70-90 mW/m（2），提供了第一个可用的格陵兰西部近海热流估计值。现代油气分布和历史流体运移受下伏古裂谷地形和-2.7Ma以来多次陆棚边缘冰川作用的影响。梅尔维尔湾脊的持续抬升，以及冰川沉积物的重新分布和均衡补偿导致的盆地边缘向盆地内倾斜，导致了海岭上方新生代地层中天然气的集中。此外，在冰川-间冰期循环期间，地下条件的反复变化可能促进了流体的再运移，并可能导致水库渗漏和增加流体通过断层的运移。在650米水深处的天然气水合物产状的顶部远低于无水合物的气相边界（-350米），目前的底层水温为1.5摄氏度，这表明该水合物区主要通过其底部的膨胀和分解来适应冰川-间冰期的变化，并且对目前的全球变暖水平相对惰性。与冰川有关的离解作用可能对目前在GHSZ下观察到的大量游离气体聚集有重要贡献。
An extensive 3D seismic dataset was used to investigate the contemporary hydrocarbon distribution and historical fluid migration in Melville Bay offshore northwest Greenland, providing the first inventory of shallow gas and gas hydrate along this part of the Greenland margin. The shallow gas anomalies vary in seismic character and have been subdivided into four categories that represent (I) isolated shallow gas, (II) free gas trapped at the base of the gas hydrate stability zone (GHSZ), (III) gas charged glacial clinoforms and (IV) a giant mass transport deposit gas reservoir. Gas hydrate deposits have been identified across an area of 537 km(2) via the identification of a discontinuous bottom simulating reflector (B SR) that marks the base of the GHSZ. The BSR has been used to estimate a geothermal gradient of 49 degrees C/km across the GHSZ and a heat flow of 70-90 mW/m(2) , providing the first publically available heat flow estimates offshore western Greenland. The contemporary hydrocarbon distribution and historical fluid migration is influenced by the underlying paleo-rift topography and multiple shelf edge glaciations since -2.7 Ma. Continued uplift of the Melville Bay Ridge, as well as glacial-sediment redistribution and basinward margin tilting from isostatic compensation, have led to a concentration of gas within the Cenozoic stratigraphy above the ridge. Furthermore, repeated variations in subsurface conditions during glacial-interglacial cycles likely promoted fluid remigration, and possibly contributed to reservoir leakage and increased fluid migration through faults. The top of the gas hydrate occurrence at 650 m water depth is well below the hydrate-free gas phase boundary (-350 m) for the present bottom-water temperature of 1.5 degrees C, suggesting this hydrate province mainly adjusted to glacial-interglacial changes by expansion and dissociation at its base and is relatively inert to current levels of global warming. Glacial-related dissociation may have significantly contributed to the numerous free gas accumulations observed below the GHSZ at present day.