|Gas bubble nucleation and growth in cohesive sediments|
Van Kesteren, W.; van Kessel, T. (2002). Gas bubble nucleation and growth in cohesive sediments, in: Winterwerp, J.C. et al. (Ed.) (2002). Fine sediment dynamics in the marine environment. Proceedings in Marine Science, 5: pp. 329-341
In: Winterwerp, J.C.; Kranenburg, C. (Ed.) (2002). Fine sediment dynamics in the marine environment. Proceedings in Marine Science, 5. Elsevier: Amsterdam. ISBN 0-444-51136-9. XV, 713 pp., more
In: Proceedings in Marine Science. Elsevier: Amsterdam. ISSN 1568-2692, more
gas production; mud; sludge depots; gas accumulation
|Authors|| || Top |
- Van Kesteren, W.
- van Kessel, T., more
Sediment often contains a significant amount of organic material, which can be decomposed by bacterial activity. During this process and under anaerobic conditions that prevail in sediments, mainly methane and carbon dioxide are formed. These compounds will dissolve in the pore water, until the level of saturation is attained.
Experiments show that gas bubble nucleation occurs already at a small oversaturation of methane in pore water. During nucleation, the large solid-liquid interfacial area acts as a catalyst. Bubbles will start to grow, as gas that does not flow out by convective or diffusive transport accumulates in bubbles. As a result of bubble initiation the distance across which transport occurs (to the closest bubble) strongly decreases; the rate of transport therefore increases and finally equals the rate of gas production. The average distance between bubbles is therefore determined by the rate of gas production and generally is in the order of millimetres to centimetres.
From a stability analysis it appears that bubbles in sludge depots may rise once the diameter is tens of centimetres. However, the average bubble diameter remains limited to a few centimetres owing to the large number of bubbles per in 3 and the total volume of gas that can be produced. During bubble growth the amount of deformation energy stored in the grain matrix increases. Crack formation will occur if this amount exceeds the fracture energy and if the stress conditions are suitable. Cracks initially have a plain, closed structure, but may eventually open depending on the depth (i.e. ambient pressure), so that discharge of gas and water can occur.