Effect of heat diffusion in the burden on the dissociation of methane in a hydrate bearing formation

• Unsteady state heat diffusion through over and under burdens reduces production at the initial stage.
• Heat diffusion helped in production at the later stage.
• Heat diffusion in the burden was restricted within few metres from the formation.
• Overall increase in formation temperature, and an enhanced production from local heating.
• The formation temperature and the net production were moderately sensitive to the thermal diffusivity of the burden.

Production of methane from sediments containing methane hydrates has been studied by researchers through the mathematical models of three phase reactive flow through porous media. This article incorporates in the model the unsteady state heat conduction through the burden and a point heat source in the formation, at a distance from the production well. Saturations and pressure in space and time were modelled using explicit finite difference method. The equation for heat conduction in the hydrate bearing formation was solved implicitly. The equation for heat conduction in the burden was solved with a coupling term from the heat balance equation for the pay-zone. A temperature profile within the burden was observed within few metres from the pay-zone. Beyond this region, the temperature did not change to any appreciable extent. The conduction of heat in the burden resulted in a more uniform temperature along the length of the pay-zone. Consequently, the movement of the dissociation front was found slower, and the production rate decreased. However, at a later stage, the pay-zone temperature was found less uniform along the length axis. The production rate recovered somewhat at this stage. The effect of thermal diffusivity of the burden on the temperature profile and the production rate is presented in this article. The presence of heat source term resulted in increased gas saturation, reduced hydrate saturation, and a higher pressure near the heating zone. The overall temperature of the pay-zone and the production rate increased due to the presence of the heat source.