Gas hydrate growth and dissociation in narrow pore networks: capillary inhibition and hysteresis phenomena
Gas hydrate growth and dissociation in narrow pore networks: capillary inhibition and hysteresis phenomena
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DOI：
10.1144/sp319.12
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Ross Anderson;B. T. Kalorazi;B. Webber
中科院分区：
文献类型：
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作者：
Ross Anderson;B. T. Kalorazi;B. Webber
摘要 含有天然气水合物的海洋沉积物通常是细粒的（淤泥、泥浆、粘土），平均孔径非常窄（∼0.1 µm）。这导致人们推测毛细管现象可能在控制海底水合物分布方面发挥重要作用，并且可能在一定程度上造成了观测到的和预测的（根据体相平衡）水合物稳定区（HSZ）厚度之间的差异。最近的许多实验室研究已经证实水合物抑制与孔径之间存在密切关系，在狭窄的孔隙中稳定性会降低；然而，迄今为止，焦点一直是多孔介质中的水合物解离条件，而对同样重要的水合物生长过程的毛细管控制在很大程度上被忽视。在这里，我们提出了合成介孔二氧化硅在一系列压力-温度 (PT) 条件（273-293 K，至 20 MPa）和孔径分布下的实验甲烷水合物生长和解离条件。结果表明，窄孔网络中水合物的形成和分解具有明显的滞后现象：固体生长发生在比解离明显更低的温度（或更高的压力）下。滞后现象采用可重复、不可逆的闭合初级生长和解离 PT 回路的形式，其中可以遵循各种特征性次级“扫描”曲线路径。最近在多孔介质中的冰-水系统中观察到类似的行为，并且是介孔材料中液-气转变的特征。这种滞后现象的原因尚未完全清楚。我们的结果表明水合物生长过程中的孔隙堵塞是主要原因。
Abstract Marine sediments hosting gas hydrates are commonly fine-grained (silts, muds, clays) with very narrow mean pore diameters (∼0.1 µm). This has led to speculation that capillary phenomena could play an important role in controlling hydrate distribution in the seafloor, and may be in part responsible for discrepancies between observed and predicted (from bulk phase equilibria) hydrate stability zone (HSZ) thicknesses. Numerous recent laboratory studies have confirmed a close relationship between hydrate inhibition and pore size, stability being reduced in narrow pores; however, to date the focus has been hydrate dissociation conditions in porous media, with capillary controls on the equally important process of hydrate growth being largely neglected. Here, we present experimental methane hydrate growth and dissociation conditions for synthetic mesoporous silicas over a range of pressure–temperature (PT) conditions (273–293 K, to 20 MPa) and pore size distributions. Results demonstrate that hydrate formation and decomposition in narrow pore networks is characterized by a distinct hysteresis: solid growth occurs at significantly lower temperatures (or higher pressures) than dissociation. Hysteresis takes the form of repeatable, irreversible closed primary growth and dissociation PT loops, within which various characteristic secondary ‘scanning’ curve pathways may be followed. Similar behaviour has recently been observed for ice–water systems in porous media, and is characteristic of liquid–vapour transitions in mesoporous materials. The causes of such hysteresis are still not fully understood; our results suggest pore blocking during hydrate growth as a primary cause.