Feasibility study on joint exploitation of methane hydrate with deep geothermal energy

With the drastic increase in energy consumption, both the natural gas hydrates and geothermal resources have become research focuses in the world due to their enormous reserves. Then the method to exploit shallow gas hydrates together with deep geothermal resources becomes attractive. In this method, seawater will be injected into the deep geothermal reservoirs and then bring into the shallow hydrate reservoirs after circulation and absorbing enough heat from the deep geothermal reservoir. Depressurization and thermal recovery technique are used to encourage the decomposition of gas hydrates. In this paper, the feasibility of the joint exploitation method is evaluated through numerical simulation, and the thermal properties of hydrate bearing sediment, exploiting parameters and reservoir sensitivities studied. Results show that effective utilization of geothermal resources to heat seawater may enable the temperature of seawater entering the hydrate layer to maintain on a level of about 50℃, and higher gas production will achieved comparing to the method of heat injection and depressurization techniques. It is indeed a method with good feasibility. Some factors, such as injecting rate, bottom hole pressure, thermal conductive factor of formation and geothermal gradient, have a significant impact on the exploiting results. In addition, the injection rate and bottom hole pressure may bring greatly influence to gas production in the early stage, while the thermal conductivity of larger formation has a favorable contribution to the heat exchange between the seawater and formation. Results also suggest that the performance of heat transferring of the method be largely attenuated and the cumulative gas production of methane be substantially reduced within the area with a geothermal gradient lower than 0.025m/℃. In such a circumstance, the commercial value of the deposits and their feasibility of exploitation will decrease.