温度梯度对非饱和粗砂中甲烷水合物形成过程的影响

Effect of temperature gradient on process of methane hydrate formation in non-saturated coarse sand

采用0.18,0.11,0.07,0.02,0和-0.02℃/cm这6种温度梯度进行水合物的形成实验。利用电阻率方法,研究温度梯度对水合物的成核和生长、粗砂中水合物饱和度以及水合物分布状况的影响。实验结果表明:温度梯度对粗砂中水合物的形成过程具有非常明显的影响。随着温度梯度的增大,成核时间缩短,反应所需过冷度先增大随后保持稳定,过冷度同时受粗砂含水量的影响。形成速率随温度梯度先增加后减小,在0.11℃/cm时,形成速率最大。在温度梯度为0.07℃/cm时,粗砂中水合物分布最均匀;当温度梯度高于或者低于0.07℃/cm时,粗砂中水合物将在不同的区域发生富集。粗砂中水合物的饱和度随温度梯度的增大逐渐增大,当温度梯度到0.11℃/cm时,甲烷水合物的饱和度达到最大。

The formation processes of methane hydrate in the coarse sand under the conditions of six different temperature gradients 0.18, 0.11, 0.07, 0.02, 0 and -0.02℃/cm were discussed. In order to study the effect of temperature gradients on the nucleation time, undercooling degree, reaction rate, saturation and distribution of the methane hydrate, the resistivity between different layers of coarse sand was monitored. The experimental results show that temperature gradient has a significant influence on the hydrate formation processes in the coarse sand. With the increase of the temperature gradient, the hydrate nucleation time is reduced a lot, while the undercooling degree required for the reaction increases first, and then reaches maximum. At the same time, the undercooling degrees are also affected by the water content of coarse sand. The reaction rate is accelerated at first and then declines with the increasing temperature gradients. The temperature gradient of the best hydrate formation rate is 0.11 ℃/cm. From the point of distribution, the hydrate is in the most uniform state at 0.07℃/cm. When the temperature gradient is less or bigger than 0.07 ℃/cm, the hydrate will gather in different layers. According to the final reaction results, the saturation of hydrate in the coarse sand increases with the rise of the temperature gradients. However, the increasing trend of saturation will stop when the temperature gradient is over 0.11℃/cm.