海底模拟反射面

海底模拟反射面（英语：bottom simulating reflectors) 是在地震反射剖面上一种浅层的地震反射面，其特征在于其反射形状类似于海底反射面。但它的反射极性与海底反射极性相反，并且经常与主要反射层理交叉^[1]。

地震波反射的原因

钻井结果证明，海底模拟反射面大致与沉积物含天然气水合物（可燃冰）底部吻合。反射主要是由可燃冰下方沉积物中含有游离气体引起的。沉积物中的气体会降低沉积物的声阻抗，因此会在含气地层的界面处产生高振幅反射。深海沉积物中可燃冰的形成取决于其环境压力和温度，这两者均受海底深度的影响。这是海底模拟反射面与地震剖面上的海底反射大体平行的主要原因^[2].

形成与分布

可燃冰由天然气和水分子组成，天然气主要是甲烷，被锁住在固体水分子晶格中。在比地表高的压力和低的温度下，甲烷与水能结合而形成可燃冰。因此，海底模拟反射面广泛存在于北极永冻土区和深水大陆边缘海底下方的浅层沉积物中^[3]。

应用

地质灾害研究

深海沉积物中可燃冰的识别对于海上石油勘探至关重要。如果在钻井前没有安装适当的设备，如果穿透含可燃冰的沉积物可能会发生井喷。此外，海洋沉积物中可燃冰的存在可能会改变海底的稳定性，并导致海底坍塌^[4]^[5].

替代能源

目前的生产技术用于开发可燃冰，尚未达到商业可行性，但可燃冰在全球广汎的分布，仍被认为是一种未来的替代能源。虽然海底模拟反射面可大略评估可燃冰区域分布面积。但估计其潜在储量，必需要其他技术来推算可燃冰层的厚度^[6]. 此外，地震采集参数及沉积物孔隙中游离气体的声学特性都可能影响声阻抗对比度，从而影响反射幅度。这就导致海底模拟反射面与可燃冰存在之间关系的不确定性^[7].

气候影响

监测海底模拟反射面的变化有助于了解可燃冰的稳定性。由于可燃冰仅在低温和中等压力范围内稳定，大气和海洋变暖可能引发可燃冰的不稳定并从永冻土和海洋沉积物中释放大量甲烷。这可能会加剧对地球气候的温室效应^[8]。

参考文献

^ Shedd, W., R. Boswell, M. Frye, P. Godfriaux, and K. Kramer (2012), Occurrence and nature of “bottom simulating reflectors” in the northern Gulf of Mexico, Mar. Pet. Geol., 34(1), 31– 40, doi:10.1016/j.marpetgeo.2011.08.005.
^ Haacke, R. R., G. K. Westbrook, and R. D. Hyndman (2007), Gas hydrate, fluid flow and free gas: Formation of the bottom-simulating reflector, Earth Planet. Sci. Lett., 261(3), 407– 420, doi:10.1016/j.epsl.2007.07.008.
^ Sloan, E. D., and C. Koh (2007), Clathrate Hydrates of Natural Gases, CRC press, Boca Raton, Fla.
^ Maslin, M., M. Owen, R. Betts, S. Day, T. Dunkley Jones, and A. Ridgwell (2010), Gas hydrates: Past and future geohazard?, Philos. Trans. A. Math. Phys. Eng. Sci., 368(1919), 2369– 2393, doi:10.1098/rsta.2010.0065..
^ Phrampus, B. J., and M. J. Hornbach (2012), Recent changes to the Gulf Stream causing widespread gas hydrate destabilization, Nature, 490(7421), 527– 530, doi:10.1038/nature11528.
^ Boswell, R., and T. S. Collett (2011), Current perspectives on gas hydrate resources, Energy Environ. Sci., 4(4), 1206– 1215, doi:10.1039/c0ee00203h.
^ Urmi Majumdar,Ann E. Cook,William Shedd,Matthew Frye (2016), The connection between natural gas hydrate and bottom-simulating reflectors.Geophys. Res. Lett., 43,7044-7051. doc:10,1002/2016GL069443.
^ Archer, D., B. Buffett, and V. Brovkin (2009), Ocean methane hydrates as a slow tipping point in the global carbon cycle, Proc. Natl. Acad. Sci. U.S.A., 106(49), 20,596– 20,601, doi:10.1073/pnas.0800885105.

[”Shedd”-1] Shedd, W., R. Boswell, M. Frye, P. Godfriaux, and K. Kramer (2012), Occurrence and nature of “bottom simulating reflectors” in the northern Gulf of Mexico, Mar. Pet. Geol., 34(1), 31– 40, doi:10.1016/j.marpetgeo.2011.08.005.

[”Haacke”-2] Haacke, R. R., G. K. Westbrook, and R. D. Hyndman (2007), Gas hydrate, fluid flow and free gas: Formation of the bottom-simulating reflector, Earth Planet. Sci. Lett., 261(3), 407– 420, doi:10.1016/j.epsl.2007.07.008.

[”Sloan”-3] Sloan, E. D., and C. Koh (2007), Clathrate Hydrates of Natural Gases, CRC press, Boca Raton, Fla.

[”Maslin”-4] Maslin, M., M. Owen, R. Betts, S. Day, T. Dunkley Jones, and A. Ridgwell (2010), Gas hydrates: Past and future geohazard?, Philos. Trans. A. Math. Phys. Eng. Sci., 368(1919), 2369– 2393, doi:10.1098/rsta.2010.0065..

[”Phrampus”-5] Phrampus, B. J., and M. J. Hornbach (2012), Recent changes to the Gulf Stream causing widespread gas hydrate destabilization, Nature, 490(7421), 527– 530, doi:10.1038/nature11528.

[”Boswell,”-6] Boswell, R., and T. S. Collett (2011), Current perspectives on gas hydrate resources, Energy Environ. Sci., 4(4), 1206– 1215, doi:10.1039/c0ee00203h.

[”Majumdar”-7] Urmi Majumdar,Ann E. Cook,William Shedd,Matthew Frye (2016), The connection between natural gas hydrate and bottom-simulating reflectors.Geophys. Res. Lett., 43,7044-7051. doc:10,1002/2016GL069443.

[”Archer”-8] Archer, D., B. Buffett, and V. Brovkin (2009), Ocean methane hydrates as a slow tipping point in the global carbon cycle, Proc. Natl. Acad. Sci. U.S.A., 106(49), 20,596– 20,601, doi:10.1073/pnas.0800885105.

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