Abstract:

During the extraction and transportation of crude oil in subsea or cold regions, gas hydrates can form and accumulate within pipelines under low-temperature and high-pressure conditions. This can subsequently lead to blockage in pipelines and valves, causing a significant threat to the safety of oil and gas transportation. Therefore, studying the formation of hydrates in oil and gas pipelines has always been the focus of attention of the oil and gas production and transportation departments. In this work, we applied a high-pressure microscopic experimental device of visualizing hydrate film growth to study the morphology and growth characteristics of methane hydrate film on the surface of microdroplets suspended in toluene, mixed oil phase of toluene and n-heptane (1∶1, volume ratio), and n-heptane by using the pendant droplet method, and the kinetics of methane hydrate film growth at different temperatures (274.15—277.15 K) and pressures (5.37—7.26 MPa) were determined. The experimental results show that the growth rate of hydrate film increases with the increase of methane solubility in different oil phases, the film growth rate (at 274.15 K, 6 MPa) in toluene (0.26 mm/s)>in mixed oil (0.23 mm/s)>in n-hexane (0.21 mm/s). During thickening growth of hydrate, water is transferred outward through the hydrate film causing the “grooves” between wrinkles on the hydrate film surface gradually filled with hydrate crystals, and the rough hydrate formed in toluene allows for the fastest thickening rate, while the smooth hydrate film formed in n-heptane allows for the slowest thickening rate. The decrease in temperature and the increase in pressure both lead to an increase in the lateral growth rate of hydrate films. The pressure has a more significant effect than temperature, and the growth rate is the slowest in toluene and the fastest in n-hexane. A model driven by pressure difference effectively predicts the kinetic data for methane hydrate film growth (AARD=6.12%).

Key words: oil-gas transportation, methane hydrate, hydrate film, kinetics, morphology

摘要：

在海底或寒冷地区原油的开采和运输过程中，当达到气体水合物形成的温度和压力条件后，水合物会在管道内形成和聚集，进而堵塞管道、阀门等，威胁油气运输安全。因此，研究水合物在油气输送管道中的形成问题一直是油气生产和运输部门关注的焦点。本实验应用高压可视水合物膜生长微观实验装置，采用悬滴法对悬垂在甲苯、甲苯与正庚烷混合油相（1∶1，体积比）、正庚烷中的微水滴表面甲烷水合物膜形貌与生长特性进行研究，测定了不同温度（274.15~277.15 K）和压力（5.37~7.26 MPa）下甲烷水合物膜生长动力学数据。实验结果表明，水合物膜生长速率随甲烷在不同油相中的溶解度增大而增大，膜生长速率（274.15 K，6 MPa）在正庚烷中（0.26 mm/s）>混合油中（0.23 mm/s）>甲苯中（0.21 mm/s）。水合物膜增厚生长过程中水通过膜向外转移，使得水合物膜上的褶皱间的“沟壑”逐渐被增厚生长的水合物填平，甲苯中形成的水合物表面粗糙增厚速率最快而正庚烷中形成的水合物膜表面光滑增厚速率最慢。温度的降低和压力的增加都使得水合物膜横向生长速率增加，其中压力的影响比温度更显著，且生长速率均呈现在甲苯中最慢正庚烷中最快。以压力差为驱动力的模型可很好地预测甲烷水合物膜生长动力学数据（AARD=6.12%）。

关键词: 油气混输, 甲烷水合物, 水合物膜, 动力学, 形态学