In the current numerical simulation studies, bottom water in Class II hydrate bearing layers is represented by grids with high water saturation which significantly extends the calculation time if the volume of the bottom water is large or grid size is small. Moreover, the influence of the bottom water volume on the depressurization performance of Class II hydrate-bearing layers has not been fully investigated. In this study, the Fetkovich analytic aquifer model was coupled with a simulation model of a hydrate reservoir to accelerate the simulation of Class II hydrate-bearing layers. Then the simulation results and calculation time were compared between the coupled model and the model in which the bottom water layer is only represented by grids. Finally, the influence of the bottom water volume on the productivity of gas and water in the depressurization method was investigated and the variation of pressure, temperature and hydrate saturation during the production process was analyzed. The results show that the coupled model can significantly reduce the simulation time of Class II hydrate bearing layer while ensuring calculation accuracy. When the pore volume of the aquifer increases to 20 times that of the bottom water layer, the computation time of single model in which bottom water layer is represented by grids is 18.7 times that of the coupled model. Bottom water invasion slows down the depressurization, and therefore, the larger the aquifer, the lower the peak value of gas production, and the later it appears. However, the invading bottom water can provide heat for hydrate dissociation; therefore, the gas production rate of the hydrate-bearing layer with bottom water is higher than that of the hydrate-bearing layer without bottom water in the late development stage. Generally, the presence of bottom water reduces the cumulative gas production and increases the cumulative water production; therefore, the larger the aquifer, the more unfavorable the depressurization development of the hydrate-bearing layer.

中文翻译：

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基于解析含水层模型的Ⅱ类水合物含水层生产动态分析

目前的数值模拟研究中，Ⅱ类水合物层底水以含水饱和度高的网格表示，如果底水体积大或网格尺寸小，计算时间显着延长。此外，底部水量对Ⅱ类含水合物层降压性能的影响尚未得到充分研究。在这项研究中，Fetkovich 分析含水层模型与水合物储层模拟模型相结合，以加速对 II 类水合物层的模拟。然后比较了耦合模型与底水层仅用网格表示的模型的模拟结果和计算时间。最后，考察了减压法底水体积对气水产率的影响，分析了生产过程中压力、温度和水合物饱和度的变化。结果表明，耦合模型可以在保证计算精度的同时，显着减少Ⅱ类含水合物层的模拟时间。当含水层孔隙体积增加到底水层孔隙体积的20倍时，以网格表示底水层的单一模型的计算时间是耦合模型的18.7倍。底水侵入减缓了降压过程，因此含水层越大，产气峰值越低，出现的时间越晚。然而，侵入的底水可以为水合物分解提供热量；因此，在开发后期，有底水的含水合物层的产气速率高于无底水的含水合物层。一般来说，底水的存在降低了累积产气量，增加了累积产水量；因此，含水层越大，含水合物层的降压发展就越不利。