Abstract CO2 replacement with depressurization assistance is a crossover concept that has been proposed in recent years for natural gas hydrate development. It combines the merits of two traditional methods to improve production and reduce risks. To verify the feasibility of this new method and evaluate the corresponding efficiency, experimental apparatus has been designed to simulate the horizontal interface between a CO2 injection well and a CH4 production well based on the independent extraction mechanism and well structure design. To prepare natural gas hydrate-bearing samples under conditions that conform to actual field conditions, silica sand is packed into a core-holding tube with methane gas and distilled water at appropriate pressures and temperatures. Then a horizontal extraction process with an injection well and a production well are simulated, and the parameters influencing the pressure system, such as inlet pressure (pressure of injection well), outlet pressure (pressure of production well), and confining pressure (pressure of the overburden layer), are controlled as variables and analyzed. The ratio of generated methane and injected CO2 is used to evaluate the corresponding utilization efficiency (UE) in this work. Results indicate that all these pressure parameters have certain effects on CO2 replacement behavior. Generally, the fluid flow driven by pressure differences, and the special phase equilibria properties are the essence of their influence. The feasibility of enhancing CO2 utilization efficiency with depressurization assistance is verified based on experimental data. In consideration of time and cost, the relative pressure parameters should be optimized comprehensively to maximize commercial efficiency before field application.

中文翻译：

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减压辅助CO2置换过程中甲烷气体水合物行为的实验研究

摘要 CO2 减压辅助置换是近年来提出的天然气水合物开发的交叉概念。它结合了两种传统方法的优点，以提高产量和降低风险。为验证这种新方法的可行性并评价相应的效率，基于独立的提取机理和井结构设计，设计了实验装置来模拟CO2注入井和CH4生产井之间的水平界面。为了在符合现场实际条件的条件下制备含天然气水合物样品，硅砂在适当的压力和温度下装入装有甲烷气体和蒸馏水的岩心管中。然后模拟了一个注入井和一个生产井的水平开采过程，影响压力系统的参数，如入口压力（注入井压力）、出口压力（生产井压力）和围压（覆盖层），作为变量进行控制和分析。在这项工作中，生成的甲烷和注入的 CO2 的比率用于评估相应的利用效率 (UE)。结果表明，所有这些压力参数对 CO2 置换行为都有一定的影响。一般来说，压差驱动的流体流动，以及特殊的相平衡特性是其影响的本质。基于实验数据验证了通过减压辅助提高CO2利用效率的可行性。