Abstract:

Class 1 hydrate deposits consist of an upper hydrate layer and a lower two-phase flow layer containing free gas, which are the preferred target for natural gas hydrate exploitation. This paper introduces the characteristics and trial production of the class 1 hydrate reservoirs, and reviews the related experimental and numerical simulation researches. In terms of the experimental research, the remodeling of the class 1 accumulation and the subsequent hydrate decomposition research are summarized. It is found that most of the experimental studies on class 1 hydrate reservoirs have certain limitations in reservoir shaping. The underlying gas of hydrate reservoirs synthesized in many experimental studies is pure gas without porous media, which cannot simulate the mass transfer process of class 1 hydrate reservoirs. Moreover, the gas production rate in different gas production stages is significantly different, and the gas production rate in the initial stage is faster. It is assumed that the model establishment idea that hydrate decomposition occurs on a sharp interface is not applicable to the numerical simulation study of the class 1 hydrate reservoir decomposition because the class 1 hydrate reservoir has multiple decomposition fronts at the same time during the decomposition stage. The future research direction of the class 1 deposits is also proposed. It is suggested to expand the research scale and simulate the stress of hydrate reservoirs in natural marine environment, so as to be closer to the natural hydrate accumulation environment and improve the reference of experimental results.

Key words: class 1 hydrate deposits, remodeling, heat transfer, mass transfer, numerical simulation

摘要：

第一类天然气水合物藏由上部含水合物沉积层和下伏气-液两相流层组成，是目前天然气水合物开采的首选目标。本文对第一类天然气水合物藏特征及试采情况进行了介绍，并回顾了相关实验和数值模拟研究进展。实验研究方面总结了第一类水合物储层的重塑方案和该类水合物藏的产气特性。指出第一类水合物藏在储层塑造方面存在一定的局限性，多数实验研究中合成的水合物储层其下伏气是没有多孔介质的纯气体，不能模拟实际带有下伏气层的水合物储层的传质过程。而且，不同产气阶段的产气速率差异明显，初始阶段产气速率明显更快。此外，适用于经典的第三类水合物藏分解特性的建模思路，即将甲烷水合物的分解描述为移动边界问题，假设水合物分解发生在尖锐界面上，不适用于第一类水合物藏分解的数值模拟研究，因为该类水合物储层在分解阶段同时出现多个分解前沿。文中同时提出了有关第一类水合物藏开发未来的研究方向，即扩大研究尺度和模拟自然海洋环境水合物储层受力情况，以更贴近自然水合物成藏环境，提高研究结论的可参考性。

关键词: 第一类水合物藏, 重塑, 传热, 传质, 数值模拟