Evaluation of Gas Production from Methane Hydrate Sediments with Heat Transfer from Over-Underburden Layers

To clarify the dissociation characteristics by depressurization with heat flow rate from over-underburden layers (Q(ov)), the effects of different Q(ov) levers on gas production by depressurization were analyzed with various initial hydrate saturations in a 5 L pressure vessel. The ratio of sensible heat of the hydrate sediments to hydrate dissociation latent heat (Delta H-Sen/Delta HL), the accumulated volume of gas production, the percentage of gas production, and the rate of gas production were obtained and compared. The effects of Delta H-Sen and Q(ov) on gas production in the fast depressurization stage and the stable temperature stage were analyzed separately during the gas production process. A sharp increase of temperature and pressure was observed which was caused by the latent heat of ice formation during the fast depressurization stage. It is concluded that the Q(ov) has a positive influence on gas production during the stable temperature stage after the total consumption of Delta HSen. The Q(ov) effectively increased the production temperature, rate of gas production, and percentage of gas production under these experimental conditions. With increased Q(ov), the promotion effects are different depending on Delta H-Sen and Shi. High Q(ov) had a remarkable influence on the rate of gas production and the percentage of gas production for the high Shi sample. In this experiment, va increased from 1.33 to 2.24 SL/M depending on the Q(ov), an increase of 68.42%. In addition, with high Q(ov), the upward migration of free water decreased the thermal conductivity of the hydrate sediments, which would decrease the rate heat flow from Q(ov).