Analysis Of Heat Transfer Effects On Gas Production From Natural Gas Hydrate

Natural gas hydrates are considered as a potential energy source because of vast reserves, their high energy capacity and reduced pollution from combustion. However, the exploitation of gas hydrates is still facing many technical problems and security issues. The dissociation of natural gas hydrate is an endothermic process. The heat transfer affect the process of dissociation and gas production. The study of analysis of heat transfer effect gas production of natural gas hydrate is meaningful to the exploitation of natural gas hydrate safety and efficiently.In this study, a two-dimensional axisymmetric simulator is developed to model the effects of heat transfer on the process of hydrate dissociation in porous media by depressurization. A series of simulations are performed to study sensible heat effects on the sediment, heat flow transfer in the cap-and base-sediment, and the effects of conductive and convective heat transfer on gas production from natural gas hydrate dissociation. Three methods are used:depressurization, thermal stimulation and combination of depressurization and thermal stimulationThe results indicated that:(1) Higher thermal conductive of sediment improve the gas production rate by depressurization, but it don’t promote the gas production rate at first period time of dissociation by thermal stimulation and combination method.(2) The gas production is primarily affected by heat flow from the cap-and base-sediment when natural gas hydrate dissociation by depressurization.(3) Convective heat transfer slightly affect the gas production rate by depressurization, but hardly affect the gas production rate by thermal stimulation and combination method.(4) The sediment material and the water content are two factors that significantly affect heat transfer in the sediment. Increasing the specific heat capacity of the sediment material increases the initial sensible heat in the core and clearly increases the gas production rate by depressurization. However, the water inhibits hydrate dissociation. When natural gas hydrate is dissociated by thermal stimulation and combination method, increasing the specific heat capacity of the sediment material and initial water saturation block the heat transfer in sediment and inhibit the dissociation of natural gas hydrate.