An improved model for simulating the behavior of oil and gas releases from ultra deep-water.

摘要

The water depths to many of the oil and gas resources easily exceed 1000m. At these depths, the high pressure and cold temperatures combine to convert the gases (if they are already in gas form) to hydrates, which is a mixture of gas and water with a consistency like frazil ice. The conversion to hydrates is a physical process that is totally reversible. The gas hydrates are lighter than water and hence move upward. Hydrates slowly dissolve while they move upward. When they reach areas that are of lower pressure in regions nearer to the water surface they also start to dissociate and get converted to gas. Such released gas also dissolves in water. When gas is released, initially, the dynamics become important and the behavior is like a jet or plume. As they get dispersed the dynamics of the plume becomes unimportant, but gases and hydrates are still subjected to advection and dispersion. This thesis presents an improved model that is complete with the above mentioned dynamic and non-dynamic behavior including thermodynamics and hydrodynamics of the plume. It has many processes that have not been modeled previously such as, the behavior of multiple bubble sizes in gas/hydrate jets and plume, hydrate dissolution, use of different Terminal Level of Plume Dynamics (TLPD)s to determine the level where dynamics become negligible, and hydrate crumbling and reformation allowing partial exposure of gas core through hydrate coat on gas bubbles for dissolution.;Previous models were developed for oil and gas blowouts with emphasis on oil fate. The model in this thesis focuses on gas fate and transport and makes comprehensive simulations from the point of release in the deep ocean until all gas and hydrate are dissolved in water or they reach the surface. This thesis contains the model formulation, comparison of model results with available experimental data, several simulations of several possible scenarios, and a parametric study investigating different criteria for transition from dynamic stage to passive conditions and effect of strong cross flow on plume behavior.