We present results from 30 quantitative degassing experiments of pressure core sections collected during The University of Texas-Gulf of Mexico 2-1 (UT-GOM2-1) Hydrate Pressure Coring Expedition at Green Canyon Block 955 in the deep-water Gulf of Mexico as part of The University of Texas at Austin–US Department of Energy Deepwater Methane Hydrate Characterization and Scientific Assessment. The hydrate saturation (Sh), the volume fraction of the pore space occupied by hydrate, is 79% to 93% within sandy silt beds (centimeters to meters in thickness) between 413 and 442 m below seafloor in 2032 m water depth. Sandy silt intervals are characterized by high compressional wave velocity (Vp) (2515–3012 m s−1) and are interbedded with clayey silt sections that have lower Sh (2%–35%) and lower Vp (1684–2023 m s−1). Clayey silt intervals are composed of thin laminae of silts with high Sh within clay-rich intervals containing little to no hydrate. Degassing of single-lithofacies sections reveals higher-resolution variation in Sh than is possible to observe in well logs; however, the average Sh of 64% through the reservoir is similar to well log estimates. Gas recovered from the hydrates during these experiments is composed almost entirely of methane (99.99% CH4, <100 ppm C2H6 on average), with an isotopic composition (δ13C: −60.4‰ and −63.6‰ Vienna Peedee belemnite and δ2H: −178.2‰ and −179.0‰ Vienna standard mean ocean water) that suggests the methane is primarily from a microbial source. A subset of six degassing experiments performed using very small pressure decrements indicates that the salinity within these samples is close to the average seawater concentration, suggesting that hydrate either formed slowly or formed during a rapid event at least tens of thousands of years before present.

中文翻译：

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墨西哥湾深水淤泥储层中的高浓度甲烷水合物

我们将德克萨斯大学墨西哥湾 2-1 (UT-GOM2-1) 水合物压力取芯探险期间在墨西哥湾深水区 Green Canyon Block 955 期间收集的 30 个压力岩心段定量脱气实验结果作为德克萨斯大学奥斯汀分校的一部分 - 美国能源部深水甲烷水合物表征和科学评估。水合物饱和度 (Sh)，即水合物占据的孔隙空间的体积分数，在 2032 米水深的海底以下 413 至 442 米之间的砂质粉砂层（厚度为厘米至米）内为 79% 至 93%。砂质粉砂层段以高压缩波速度 (Vp) (2515–3012 ms-1) 为特征，并与具有较低 Sh (2%–35%) 和较低 Vp (1684–2023 ms-1) 的粘土质粉砂岩段互层. 粘土质粉砂层段由富含粘土层段内含有很少或不含水合物的高 Sh 粉砂薄层组成。单岩相剖面的脱气揭示了比测井中可能观察到的更高分辨率的 Sh 变化；然而，通过储层的 64% 的平均 Sh 与测井估计值相似。在这些实验中从水合物中回收的气体几乎完全由甲烷组成（99.99% CH4，平均<100 ppm C2H6），具有同位素组成（δ13C：-60.4‰ 和-63.6‰ Vienna Peedee belemnite 和 δ2H：-178.2‰ -179.0‰ 维也纳标准平均海水）表明甲烷主要来自微生物来源。