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The gas production from methane-hydrate-bearing sediment by injecting ethylene glycol (EG) solution was investigated using a three-dimensional experimental apparatus. Eight experimental runs were performed to examine the influence of operation conditions on hydrate dissociation by EG injection. The variations of pressure and temperature distribution in the reactor stimulated by the injected EG were obtained for the gas production process of the hydrate. The variation trend of temperature in the injection stage shows a shape of a “well” because of heat transfer and hydrate dissociation. The appearance sequence of temperature “well” and “well” depth is different for every port at different depths and radii. The effects of the concentration and quantity of EG and soaking time on the gas production ratio are examined. It shows that there exists an optimal value of the mass ratio of injected EG solution to initial water, where a maximum gas production ratio appears. When other conditions are similar, the gas amount produced by hydrate dissociation increases with the increase of the inhibitor concentration. The gas production efficiency increases with the decrease of the EG quantity and the increase of the EG concentration.

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A three-dimensional middle-size reactor was used to simulate gas production from methane hydrate-bearing sand by hot-water cyclic injection. The gas production process and energy efficiency in the whole process, which was divided into injecting hot water, closing well, and producing gas (three steps), were investigated using 16 thermocouples distributed in hydrate-bearing sand samples. The experimental results indicates that the overall temperature trend increases with hot-water injection and decreases with gas production. The temperature distribution and fluctuation in the reactor depend upon the location of the injecting/producing well as well as the porosity and permeability of hydrate samples. Heat transfer is controlled by hot-water seepage flow during the injection of hot water. The affecting factors on the energy efficiency, such as hydrate saturation, hydrate sample temperature, hot-water temperature, mass of hot water injected, and well pressure, were examined. It was found that, when other conditions are similar, the energy efficiency ratio increases with the increase of the hydrate-bearing sand saturation and hydrate sample temperature but decreases with the increase of the hot-water temperature and well pressure.

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