基于相变蓄冷原理的天然气水合物钻探钻井液智能控温微胶囊研究

Natural gas hydrate drilling is faced with engineering problems and even marine geological disasters caused by the decomposition of hydrates. The temperature of the drilling fluid is the key factor of the stability of the hydrate in the formation, which is related to the safety and efficiency of the drilling operations. In order to stabilize the hydrate formation, physical cooling of the drilling fluid is currently used on the drilling platform, but it is impossible to control the temperature after the drilling fluid entering the wellbore, and it is difficult to control the decomposition of the hydrate caused by the temperature increase in the drilling fluid under the downhole engineering disturbance. For this reason, based on the concepts and new methods of phase change cool storage, this project proposes the use of phase change materials to achieve real-time control of the entire drilling fluid temperature downhole and prevent hydrate decomposition. To meet the special requirements of natural gas hydrate drilling engineering, the high-latent-heat, high-intensity phase change microcapsules with the phase transition temperatures in the range of 0-8°C will be designed and developed, and the physical and chemical mechanism of action between phase change microcapsules and drilling fluids will be explored. Then the characteristics control methods of drilling fluid containing phase change microcapsules will be established, and the intelligent temperature control water-based drilling fluid will be developed which can stabilize the hydrate formation. The research results can provide new ideas and new methods for controlling the stability of gas hydrates in drilling engineering and enrich the development of natural gas hydrate drilling fluid theory and technology.

天然气水合物钻探中面临水合物分解引起的工程乃至海洋地质灾害问题。钻井液温度是影响地层中水合物稳定性的关键因素，关系到钻井安全与效率。为了稳定水合物地层，目前采用在钻井平台对钻井液进行物理降温，但进入井筒后不再可控，无法解决井下工程扰动下钻井液温度上升造成的水合物分解。为此，本项目基于相变蓄冷理念与新方法，提出采用相变材料实现对井下钻井液温度的全过程实时控制，抑制水合物分解。针对天然气水合物钻探工程特殊要求，设计并研发高潜热、高强度且相变温度在0-8℃范围内可调的相变微胶囊处理剂，探索相变微胶囊与钻井液之间的物理化学作用机制，建立相变微胶囊钻井液特性调控方法，指导构建稳定天然气水合物地层的“智能”控温水基钻井液。研究成果可为钻井工程中水合物稳定性控制提供新思路与新方法，丰富发展天然气水合物钻探钻井液理论与技术。

天然气水合物钻探中面临水合物分解引起的工程乃至海洋地质灾害问题。钻井液温度是影响地层中水合物稳定性的关键因素，但现有的平台降温法无法解决井下工程扰动下钻井液温度上升造成的水合物分解。为此，本项目提出研发相变控温材料实现对井下钻井液温度的全过程实时控制，抑制水合物分解。根据海域天然气水合物地层钻井工程特点，采用原位聚合法制备出以正十四烷为芯材、三聚氰胺-尿素-甲醛树脂（MUF树脂）为壁材的相变微胶囊材料，并对其进行结构表征和性能评价。结果表明，制备出的正十四烷/MUF树脂相变微胶囊平均粒径约为3.8μm，相变焓为116J/g，相变温度为6℃，抗剪切强度较高，密封性较好。微胶囊的相变控温作用可显著降低钻井液的升温/降温速率，15次升温/降温循环后微胶囊的控温性能未减弱。实验分析了水基钻井液与相变微胶囊之间的物理化学作用。结果表明，钻井液的碱性条件（pH值为8-12）以及深水钻井液使用的高浓度无机/有机盐以及醇类水合物热力学抑制剂对相变微胶囊的强度及控温特性无明显影响，表明壁材与钻井液不发生反应，保证了微胶囊的稳定性。向水基钻井液中加入相变微胶囊后，钻井液的塑性粘度和滤失量稍有增加，但仍保持在合理范围内。基于深水水基钻井液基础配方，通过钻井液低温流变性和滤失性调控与优化，构建了适合海域天然气水合物钻探的智能控温水基钻井液体系，该钻井液具有良好的低温流变性、滤失造壁性及页岩抑制性，5%相变微胶囊加量下水合物分解速率降低71.6%。进一步采用反相乳液法制备出以四丁基溴化铵（TBAB）为芯材、纳米二氧化硅为壁材的相变微胶囊，包覆率达62.2%；相变焓为121.4J/g；粒径为3-10μm；相变温度在0-12.19℃范围内调；其与钻井液具有良好的配伍性，并可改善钻井液的封堵降滤失性能。研究成果为海域天然气水合物钻探过程中控制水合物分解提供了新的思路和方法，丰富发展了水合物钻探钻井液理论与技术。