水合物微观形貌调控机制及其对置换开采效率的影响研究

Natural gas hydrate is an important alternative energy resource. However, the commercial exploitation of natural gas hydrate has not been realized because of the low production efficiency. For the method of natural gas production from hydrate by CH4-CO2 replacement, the production efficiency is hindered by the transfer resistance of replacement medium and replaced gas in the newly formed CH4/CO2 hydrate layer. To address the aforesaid problem, this project proposes a method that accelerate the mass transfer of gas and water during the replacement by improving the hydrate morphology based on the different morphologies of hydrate under different additives and thermodynamic conditions. By focusing on the micro-morphology change of hydrate during replacing the methane hydrate by carbon dioxide, the effects of thermodynamic conditions and replacement media on hydrate morphology, the relationship between hydrate morphology and mass transfer resistance, the effects of hydrate morphology and combination mode between hydrate and sediment particles on replacement efficiency will be systematically studied. The critical factors that affect the hydrate morphology will be determined bases on those studies, and based on the critical factors, new additives for replacement media will be developed to form hydrate layer of high permeability. Finally, the regulation mechanism of hydrate micro-morphology and its effect on exploitation efficiency of methane hydrate with CO2 replacement will be understand, and according to these results, the exploitation efficiency of hydrate by carbon dioxide replacement would be improved.

作为一种重要的接替能源，天然气水合物目前尚未能实现商业化开采，其关键原因在于开采效率过低。对于CH4-CO2置换开采法，其开采效率极大地受到置换介质和采出气透过新形成的CH4/CO2水合物层的传质阻力影响。针对以上问题，本项目提出利用水合物在不同添加剂和热力学条件下形貌不同的特性，改善新形成的水合物形貌以促进置换过程中的气液传质。通过聚焦于置换过程中水合物微观形貌变化，重点研究热力学条件和置换介质的组成对水合物形貌的影响规律、水合物形貌与传质阻力的关系、水合物形貌以及水合物与沉积物结合形态对综合置换效率的影响规律。根据以上规律确定水合物形貌和裂隙发育的关键控制因素，依据关键控制因素开发可形成高渗水合物层的置换添加剂。最终获取水合物微观形貌调控方法及其对置换开采效率的影响规律，达到提升水合物置换开采效率的目的。

二氧化碳置换法开采天然气水合物具有实现能源开发和碳封存的双重意义。相较于其他水合物开采方法，二氧化碳置换法可维持水合物储层稳定，防止海底滑坡等地质灾害的发生。受到置换过程中新生成的水合物渗透率极低的影响，二氧化碳置换天然气水合物的效率较低。为了提高水合物置换效率，本项目重点对水合物置换过程中的形貌调控进行研究。使用纯二氧化碳、二氧化碳氢气混合气研究了不同的置换推动力、置换时间等因素对置换速率和置换过程中水合物形貌变化的影响，发现以上因素均不能使水合物在置换过程中产生裂隙。利用冰粉末模拟天然气水合物研究了水合物原位快速转化方法，确认了水合物分解和动力学促进剂在快速转化过程中的积极作用。开发了利用热力学抑制剂强化天然气水合物分解—利用动力学促进剂强化二氧化碳水合物生成的序贯强化法，确认了热力学抑制剂和动力学促进剂在水合物裂隙产生中的关键作用；利用该方法可将水合物置换时间减少至最短3分钟以内。本研究揭示了水合物置换过程中裂隙产生的关键影响因素和调控方法，可推动天然气水合物开发和水合物法二氧化碳封存技术的发展。