海域天然气水合物开采方案设计及气液分离特性分析

Design of offshore natural-gas-hydrate exploitation scheme and analysis of gas-liquid separation characteristics

为了解决海域天然气水合物开采效率低、水合物大面积分解和二次生成等问题,以我国南海海域某天然气水合物开采井为例,结合降压法和热激法设计一种海域天然气水合物整体开采方案,运用数值模拟方法研究螺旋式、轴流导叶式、管柱式分离装置在不同气液比下分离效率及分离特性,同时开展气液分离实验验证结果准确性。结果表明:海域天然气水合物开采采用双管柱结构方案,生产井采用泄流面积更大的水平井方案。螺旋式分离装置适用于10%的液相含量(体积分数),优选螺旋分离装置进行海域天然气水合物气液分离,螺旋式分离装置前两圈螺旋处压降较大,压降达到325 Pa。液滴直径25~100μm时分离效率均达到了100%,分离效率随圈数的增多而增大,变化范围为79.2%~91.8%。分离效率实验与数值分析结果误差为5%,验证了气液分离数值模拟分析结果的准确性。本研究可为高效安全开发海域天然气水合物提供重要技术支持。

The exploitation of offshore natural gas hydrates has problems of low efficiency, as well as large-area decomposition and secondary generation of hydrates. Hence, taking a production well of natural gas hydrates in the South China Sea as an example, this study combines the depressurization method and the heat shock method to design an overall exploitation scheme for offshore natural gas hydrates. The numerical simulation method is used to study the separation efficiency and separation characteristics of spiral, axial-flow guide vane, and cylindrical separation devices under different gas-liquid ratios. Meanwhile, gas-liquid separation experiments are carried out to verify the accuracy of the results. The results show that the double-string structure scheme is adopted for the exploitation of offshore gas hydrates, and the horizontal well scheme with a larger discharge area is adopted for the production well. The spiral separation device is suitable for 10% liquid phase content, which is preferred for gas-liquid separation of offshore natural gas hydrates.The pressure drop at the first two spirals of the spiral separation device is relatively large, reaching 325 Pa. The separation efficiency reaches 100% when the droplet diameter is 25~100 μm, and the separation efficiency increases with the number of turns, ranging from79.2% to 91.8%. The error between the experimental and numerical analysis results of separation efficiency is 5%, which verifies the accuracy of the numerical simulation analysis results of gas-liquid separation. This study can provide important technical support for the efficient and safe development of offshore natural gas hydrates.