天然气水合物热力学抑制剂作用机制及优化设计

基于2种典型天然气水合物生成预测理论模型,结合水合物热力学抑制剂评价实验数据以及水活度测试结果,分析了水合物热力学抑制剂影响天然气水合物生成条件的作用机制,建立了水合物生成温度降低值与水活度的关系式。结果表明,水合物热力学抑制剂降低水合物生成温度,或提高水合物生成压力的作用机制是降低溶液的水活度,其抑制水合物生成效果随水活度的降低线性增加。通过模拟深水钻井环境,对典型的水合物热力学抑制剂氯化钠,以及钻井液常用的有机盐甲酸钠进行了水活度测试以及水合物抑制效果评价实验,探讨了可降低钻井液水活度的有机盐加重剂Weigh作为水合物抑制剂的可能性。结果表明,加入氯化钠或甲酸钠降低水活度至0.84,钻井液可在1 500 m水深条件下循环16h无水合物生成;Weigh可大幅降低溶液水活度,水合物抑制效果优于氯化钠、甲酸钠以及由氯化钠和乙二醇组成的复合抑制剂。针对深水钻完井作业中遇到的必须使用低密度钻井液或完井液的情况,初步优化设计了低密度水合物抑制剂,可保证钻井液和完井液在低密度条件下(1.05~1.07g/cm3)有效抑制水合物生成。

Inhibition mechanism and optimized design of thermodynamic gas hydrate inhibitors

Based on two kinds of typical theoretical prediction models for gas hydrate formation in combination with evaluation experimental data of thermodynamic hydrate inhibitors as well as the test results of water activity, the influence mechanism of thermodynamic hydrate inhibitor on hydrate formation conditions was analyzed to establish the relation between the drop value of hydrate formation temperature and water activity. The results indicate that the effect mechanism of thermodynamic hydrate inhibitor to reduce hydrate formation temperature or increase hydrate formation pressure is to lower water activity, and the hydrate inhibition performance is increased linearly with the decrease in water activity. The deepwater drilling environment was simulated for water activity test and evaluation experiments o n hydrate inhibition performance for the typical thermodynamic hydrate inhibitor (sodium chloride) and common organic salt additive (sodium formate) of drilling fluid. Meanwhile, the possibility of organic salt weighting agent (Weigh) as hydrate inhibitor to reduce the water activity of drilling fluid was explored. The results show that no hydrate is formed in drilling fluid after 16 h cycling at 1 500 m water depth, when water activity was reduced to be 0.84 by adding sodium chloride or sodium formate. Weigh can lower water activity significantly, and its hydrate inhibition performance is better than sodium chloride, sodium formate and the composite inhibitor of sodium chloride and glycol. Aiming at the situation that low-density drilling fluid or completion fluid is necessarily required in deepwater drilling and completion, optimal design is performed to low-density hydrate inhibitor preliminarily, guaranteeing drilling fluid and completion fluid to inhibit hydrate formation effectively in case of low density (1.05~1.07 g/cm³).