用原子力显微镜研究温度和接触界面对THF水合物形貌的影响
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摘要
天然气水合物的表面形貌和性质一直是水合物研究领域的基础科学问题,它不仅制约人工环境下油气管线内水合物颗粒间聚集以及颗粒与管壁接触并阻塞管道的程度,而且还影响自然环境下水合物与沉积物骨架颗粒间接触关系以及相应的内聚力和摩擦角.本文首次运用原子力显微镜(AFM)对不同温度和不同界面合成的四氢呋喃(THF)水合物进行了表征,分析了温度和接触界面对其表面特征的影响.结果表明:在气-液界面自由生长的多晶THF水合物,生长温度越低,晶粒尺寸越小并更容易出现不定形水合物.晶粒界面的横截面呈"V"字形,其宽度和深度随生长温度降低而减小.在固-液界面受限生长的多晶THF水合物,其表面形貌和粗糙度除了受生长温度影响外还与接触的固体介质有关.当生长温度较高时晶粒尺寸较大,晶粒界面清晰可见;但生长温度较低时接触介质表面性质会影响二者分离后水合物表面形貌,如会出现微孔洞等结构且粗糙度变大,观察不到晶粒界面.这一发现对解释水合物沉积物残余强度特征与机制具有重要启示意义.
A sound knowledge of surface topography and property of natural gas hydrates is of great importance to understand the interaction between hydrate and hydrate particles, or hydrate particles with other media such as steels in petroleum pipelines and minerals in natural settings. However, a solid and effective approach to investigation on the surface topography and property of clathrate hydrates remains a longstanding challenge. Here, we firstly report the characterization of THF clathrate hydrates using atomic force microscopy(AFM). These hydrate samples grew from the THF solution liquid drop in air or confined at the liquid-solid interfaces at the temperature range from –5°C to –30°C.The results show that for THF clathrate hydrates grown at gas-liquid interface, the lower growth temperature, the smaller hydrate crystalline grains. At the same time, the shapes of these THF hydrate crystalline grains change from polygonal to amorphous. The cross section of grain boundary is "V" shape, and its width and depth decrease with the decrease of the growth temperature.The avulsed surface morphology and roughness of THF clathrate hydrate grown at the solid-liquid interface, are not only affected by the growth temperature, but also related to the solid medium. At a relatively high growth temperature, the crystalline grains are bigger, and the grain boundary can be observed. However, when the temperature is low, there are micropores on the hydrate surface and the roughness is larger. And no grain boundary can be observed. The findings have an important significance for explaining the mechanical behaviors of hydrate deposits.
A sound knowledge of surface topography and property of natural gas hydrates is of great importance to understand the interaction between hydrate and hydrate particles, or hydrate particles with other media such as steels in petroleum pipelines and minerals in natural settings. However, a solid and effective approach to investigation on the surface topography and property of clathrate hydrates remains a longstanding challenge. Here, we firstly report the characterization of THF clathrate hydrates using atomic force microscopy(AFM). These hydrate samples grew from the THF solution liquid drop in air or confined at the liquid-solid interfaces at the temperature range from –5°C to –30°C.The results show that for THF clathrate hydrates grown at gas-liquid interface, the lower growth temperature, the smaller hydrate crystalline grains. At the same time, the shapes of these THF hydrate crystalline grains change from polygonal to amorphous. The cross section of grain boundary is "V" shape, and its width and depth decrease with the decrease of the growth temperature.The avulsed surface morphology and roughness of THF clathrate hydrate grown at the solid-liquid interface, are not only affected by the growth temperature, but also related to the solid medium. At a relatively high growth temperature, the crystalline grains are bigger, and the grain boundary can be observed. However, when the temperature is low, there are micropores on the hydrate surface and the roughness is larger. And no grain boundary can be observed. The findings have an important significance for explaining the mechanical behaviors of hydrate deposits.
引文
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15 Ueno H,Akiba H,Akatsu S,et al.Crystal growth of clathrate hydrates formed with methane+carbon dioxide mixed gas at the gas/liquid interface and in liquid water.New J Chem,2015,39:8254-8262
16 Saito K,Kishimoto M,Tanaka R,et al.Crystal growth of clathrate hydrate at the interface between hydrocarbon gas mixture and liquid water.Cryst Growth Des,2011,11:295-301
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18 Tanaka R,Sakemoto R,Ohmura R.Crystal growth of clathrate hydrates formed at the interface of liquid water and gaseous methane,ethane,or propane:variations in crystal morphology.Cryst Growth Des,2009,9:2529-2536
19 Wang R,Ning F L,Liu T L,et al.Dynamic simulation of hydrate formed from free methane gas in borehole(in Chinese).Acta Petrol Sin,2017,38:963-976[王韧,宁伏龙,刘天乐,等.游离甲烷气在井筒内形成水合物的动态模拟.石油学报,2017,38:963-972]
20 Mohebbi V,Naderifar A,Behbahani R M,et al.A mass transfer study of methane and ethane during hydrate formation.Pet Sci Tech,2014,32:1418-1425
21 Chaouachi M,Falenty A,Sell K,et al.Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X-ray computed tomographic microscopy.Geochem Geophys Geosyst,2015,16:1711-1722
2 Boswell R,Collett T S.Current perspectives on gas hydrate resources.Energy Environ Sci,2011,4:1206-1215
3 Trung N N.The gas hydrate potential in the south china sea.J Pet Sci Eng,2012,88-89:41-47
4 Hester K C,Brewer P G.Clathrate hydrates in nature.Annu Rev Mar Sci,2009,1:303-327
5 Fu S Y,Lu J A.The characteristics and origin of gas hydrate in Shenhu Area,South China Sea(in Chinese).Mar Geol Front,2010,26:6-10[付少英,陆敬安.神狐海域天然气水合物的特征及其气源.海洋地质前沿,2010,26:6-10]
6 Zhang H,Lu H L,Liang J Q,et al.The methane hydrate accumulation controlled compellingly by sediment grain at Shenhu,northern South China Sea(in Chinese).Chin Sci Bull,2016,61:388-397[张辉,卢海龙,梁金强,等.南海北部神狐海域沉积物颗粒对天然气水合物聚集的主要影响.科学通报,2016,61:388-397]
7 Zhang W,Liang J Q,Lu J A,et al.Accumulation features and mechanisms of high saturation natural gas hydrate in Shenhu Area,northern South china Sea(in Chinese).Petrol Explor Dev,2017,44:670-680[张伟,梁金强,陆敬安,等.中国南海北部神狐海域高饱和度天然气水合物成藏特征及机制.石油勘探与开发,2017,44:670-680]
8 Kodama T,Ohmura R.Crystal growth of clathrate hydrate in liquid water in contact with methane+ethane+propane gas mixture.J Chem Technol Biotechnol,2014,89:1982-1986
9 Ohno H,Narita H,Nagao J.Different modes of gas hydrate dissociation to ice observed by microfocus X-ray computed tomography.J Phys Chem Lett,2011,2:201-205
10 Jin Y,Nagao J,Hayashi J,et al.Observation of Xe hydrate growth at gas-ice interface by microfocus X-ray computed tomography.J Phys Chem C,2008,112:17253-17256
11 Stern L A,Kirby S H,Circone S,et al.Scanning electron microscopy investigations of laboratory-grown gas clathrate hydrates formed from melting ice,and comparison to natural hydrates.Am Miner,2004,89:1162-1175
12 Falenty A,Salamatin A N,Kuhs W F.Kinetics of CO2-hydrate formation from ice powders:Data summary and modeling extended to low temperatures.J Phys Chem C,2013,117:8443-8457
13 Jung T A,Moser A,Hug H J,et al.The atomic force microscope used as a powerful tool for machining surfaces.Ultramicroscopy,1992,42-44:1446-1451
14 Sundararajan S,Bhushan B,Namazu T,et al.Mechanical property measurements of nanoscale structures using an atomic force microscope.Ultramicroscopy,2002,91:111-118
15 Ueno H,Akiba H,Akatsu S,et al.Crystal growth of clathrate hydrates formed with methane+carbon dioxide mixed gas at the gas/liquid interface and in liquid water.New J Chem,2015,39:8254-8262
16 Saito K,Kishimoto M,Tanaka R,et al.Crystal growth of clathrate hydrate at the interface between hydrocarbon gas mixture and liquid water.Cryst Growth Des,2011,11:295-301
17 Watanabe S,Saito K,Ohmura R.Crystal growth of clathrate hydrate in liquid water saturated with a simulated natural gas.Cryst Growth Des,2011,11:3235-3242
18 Tanaka R,Sakemoto R,Ohmura R.Crystal growth of clathrate hydrates formed at the interface of liquid water and gaseous methane,ethane,or propane:variations in crystal morphology.Cryst Growth Des,2009,9:2529-2536
19 Wang R,Ning F L,Liu T L,et al.Dynamic simulation of hydrate formed from free methane gas in borehole(in Chinese).Acta Petrol Sin,2017,38:963-976[王韧,宁伏龙,刘天乐,等.游离甲烷气在井筒内形成水合物的动态模拟.石油学报,2017,38:963-972]
20 Mohebbi V,Naderifar A,Behbahani R M,et al.A mass transfer study of methane and ethane during hydrate formation.Pet Sci Tech,2014,32:1418-1425
21 Chaouachi M,Falenty A,Sell K,et al.Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X-ray computed tomographic microscopy.Geochem Geophys Geosyst,2015,16:1711-1722
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