Transfer of hydrocarbons from natural seeps to the water column and atmosphere
Transfer of hydrocarbons from natural seeps to the water column and atmosphere
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DOI：
10.1046/j.1468-8123.2002.00023.x
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发表时间：
2002-05
期刊：
影响因子：
1.7
通讯作者：
I. MacDonald;I. Leifer;R. Sassen;P. Stine;R. Mitchell;N. Guinasso
中科院分区：
文献类型：
--
作者：
I. MacDonald;I. Leifer;R. Sassen;P. Stine;R. Mitchell;N. Guinasso
地面地球化学勘探、地震勘探和卫星遥感的结果证实了世界各地海相盆地中的油气渗漏。渗漏是碳循环的一个动态组成部分，可以是具有重要经济意义的碳氢化合物矿床的重要指标。墨西哥湾北方有数百个活跃的渗漏，可以通过使用潜艇和遥控潜水器进行实验研究。通过表层沉积物的碳氢化合物通量深刻地改变了渗漏处的底栖生态和海底地质。在水深500 - 2000米的地方，快速的气体流动会导致气体水合物的浅亚稳态沉积，这会降低沉积物的孔隙度并影响渗透率。本文详细介绍了在最后的短暂过渡期间发生的过程-石油和天然气从海底逸出，通过水上升并溶解，被微生物过程消耗，或分散到大气中。上部沉积柱的地质情况决定了排放是快速和间歇性的，如泥火山所发生的那样，还是更渐进和稳定的，如渗漏孔被气体水合物堵塞的情况。在这两种情况下，渗漏的石油和天然气似乎通过水上升，而不是分离。石油在通过水柱运输期间的化学变化相对较小，但一旦到达海面，其挥发性更强的成分就会迅速蒸发。气泡在上升时迅速溶解，尽管观察表明气泡上的油涂层抑制溶解。在海面上，浮油形成浮油，可通过遥感检测，其起源在海底喷口的横向1000米范围内。这与预测的更大距离相矛盾，如果油滴以0.01 m s-1的预期速率上升通过500 m水柱，同时受到0.2 m s-1或更大的横向电流。它表明，石油与气泡一起以0.15 m/s的速度上升到地面。
Results from surface geochemical prospecting, seismic exploration and satellite remote sensing have documented oil and gas seeps in marine basins around the world. Seeps are a dynamic component of the carbon cycle and can be important indicators for economically significant hydrocarbon deposits. The northern Gulf of Mexico contains hundreds of active seeps that can be studied experimentally with the use of submarines and Remotely Operated Vehicles (ROV). Hydrocarbon flux through surface sediments profoundly alters benthic ecology and seafloor geology at seeps. In water depths of 500‐2000 m, rapid gas flux results in shallow, metastable deposits of gas hydrate, which reduce sediment porosity and affect seepage rates. This paper details the processes that occur during the final, brief transition — as oil and gas escape from the seafloor, rise through the water and dissolve, are consumed by microbial processes, or disperse into the atmosphere. The geology of the upper sediment column determines whether discharge is rapid and episodic, as occurs in mud volcanoes, or more gradual and steady, as occurs where the seep orifice is plugged with gas hydrate. In both cases, seep oil and gas appear to rise through the water in close proximity instead of separating. Chemical alteration of the oil is relatively minor during transit through the water column, but once at the sea surface its more volatile components rapidly evaporate. Gas bubbles rapidly dissolve as they rise, although observations suggest that oil coatings on the bubbles inhibit dissolution. At the sea surface, the floating oil forms slicks, detectable by remote sensing, whose origins are laterally within � 1000 m of the seafloor vent. This contradicts the much larger distance predicted if oil drops rise through a 500 m water column at an expected rate of � 0.01 m s � 1 while subjected to lateral currents of � 0.2 m s � 1 or greater. It indicates that oil rises with the gas bubbles at speeds of � 0.15 m s � 1 all the way to the surface.