Poojitha D. Yapa

The rising cost of energy has accelerated the exploration for alternative energy resources. USA, Japan, Canada, and Brazil have found large deposits of methane or natural gas near the sea bed in deepwater, much of it in the form of hydrates. Gas hydrates are, slush like compounds in which gas molecules are trapped inside cages of water molecules. Major efforts are currently underway to bring them for use on land, increasingthe possibility of a release of gas or hydrates from deepwater. Due to high pressure and lower temperature in deepwater, a release of gas may be converted to hydrates. Being lighter than water, both gas and hydrates travel upward once released into water. Hydrates dissociate into gas and water due to lower pressure and higher temperature at higher elevations. Gas and hydrates both dissolve in water but the rate for gas is significantly higher. As they travel, gas bubbles change in size due to changes in pressure and temperature. Whether released gas reaches the water surface or not depends on all of the above described processes. If methane or natural gas reaches the water surface, it poses hazards, such as; the possibility of an explosion, loss of buoyancy on floating vessels/installations, and toxic effects for inhabitants on land near the water surface. Gas dissolved in water may adversely affect biota. A model is needed to analyze the impact of a gas release from the deepwater.

Plume rise time and height depend on the buoyant velocity of bubbles, which depends on the bubble size, i.e. bubble size distribution. Gas and hydrate dissolution change bubble sizes. While previous models included gas dissolution, hydrate dissolution was not included. Bubble surface area is proportional to size. Surface area affects the dissolution. Therefore, the effects of bubble sizes and dissolution (both gas and hydrate) are intertwined. They not only determine how fast the plume rises, but also the level of which the gas or hydrate disappears in the water column, or how much of the gas will reach the water surface.

In this project, a model (MEGADEEP) developed to comprehensively simulate the transport and fate of gases and hydrates released in deepwater. Click here for the description of the model