Axisymmetric numerical heat transfer analysis of natural gas hydrates reservoir

Abstract

Gas hydrates are crystalline substances, occurring in nature under high pressure and low temperature. Numerical studies were conducted on dissociation of gas hydrate to recover natural gas. The model is a cylindrical geometry with a wellbore at the center through which hot water is injected. Through this thermal stimulation technique frozen hydrate reservoir is melted and natural gas is released. The computational fluid dynamics software FLUENT was adopted to generate the model. The initial model was solely comprised of a hydrate layer. This model was refined by adding the overburden and the underburden to the hydrate and exploring the thermal regime of the entire composite medium. Unsteady state results showing the dissociation front propagation with respect to time were calculated. In the first part, the hydrate medium is dissociated by the conduction phenomenon only. In the second part, due to the porous nature of the hydrate medium, both conduction and convection phenomena are considered. This thesis presents the following results obtained from simulations using Fluent. They are: temperature rise within the reservoir with time, temperature profiles in the radial direction, and steady and transient state solutions of the dissociation of gas hydrate with the liquid fraction in the reservoir. Comparison of our results with a finite difference model and a finite element model is also included. Volumes of gas released with respect to time and thermal efficiency ratios are also determined.