Abstract:

In order to prove the influence of wax crystal precipitation on the phase equilibrium and nucleation characteristics of hydrate formation, this paper selected a mixed solution of 2^# industrial white oil and 60^# Kunlun paraffin to simulate the wax-containing system. Using a high-pressure visual stirred tank and combining with the visualization images during the hydrate formation process, we studied the influence of different wax concentrations on the hydrate formation phase equilibrium curve, hydrate nucleation induction time, and induction time change rate, and explored the effects of wax crystal precipitation on hydrate generation mechanism. The results show that as the concentration of wax crystals increases, the phase equilibrium conditions for hydrate formation gradually decrease, and the phase equilibrium curve shifts to the right compared to the wax-free system; the greater the wax crystal concentration, the more obvious the tendency to shift; at 281.5K and the wax content of 3.5%(mass fraction), the phase equilibrium pressure decreases by 6.5% compared with that of the wax-free system. By analyzing the effect of different wax crystal concentrations on the hydrate nucleation induction time, it is found that the precipitation of wax crystals accelerates the hydrate crystallization, shortens the hydrate nucleation induction time, and the greater the wax crystals concentration, the more obvious the shortening of the induction time. By exploring the effect of different wax crystal concentrations on the hydrate nucleation-inducing ability, it is found that with the increase of wax crystal concentration, the promotion ability of wax crystal precipitation to hydrate-induced nucleation increases at first and then decreases. By analyzing the influence of wax precipitation on the hydrate formation rate and location, it is found that when the system reaches the hydrate formation condition, the hydrate in the center of the reaction reactor is generated earlier than at the gas-liquid surface and the kettle wall. The research results are helpful to the application and development of deep sea-oil and gas exploitation, and provide reliable pVT data for studying the coupling characteristics of wax crystal and hydrate.

Key words: hydrate, phase equilibrium curve, induction time, rate of change of induction time

摘要：

为了探明蜡晶析出对水合物生成相平衡特性及成核特性的影响，本文选用2^#工业白油与60^#昆仑石蜡的混合溶液来模拟含蜡体系，利用高压可视化搅拌釜开展含蜡体系水合物生成实验，结合水合物生成过程中的可视化图像，研究不同蜡晶浓度对水合物生成相平衡曲线、水合物成核诱导时间、诱导时间变化率的影响规律及蜡晶析出对水合物生成机理的影响。结果表明：①随着蜡晶浓度的增加，水合物生成相平衡条件逐渐降低，相平衡曲线较无蜡体系向右偏移，且蜡晶浓度越大，偏移趋势越明显，在温度281.5K时，3.5%（质量分数）的蜡含量比无蜡体系的相平衡压力降低6.5%；②通过分析不同蜡晶浓度对水合物成核诱导时间的影响发现，蜡晶析出加快了水合物结晶，缩短了水合物成核诱导时间，且蜡晶浓度越大，诱导时间缩短越明显；③通过探究不同蜡晶浓度对水合物成核诱导能力的影响发现，随着蜡晶浓度的增加，蜡晶析出对水合物诱导成核的促进能力总体呈现先增大后减小的趋势，即蜡晶对水合物的促进能力不是无限增大的，会随蜡晶浓度的增加逐渐减弱；④通过分析蜡晶析出对水合物生成速率及生成位置的影响发现，当体系达到水合物生成条件时，反应釜中心部分的水合物会先于气液表面及釜壁生成。本文研究成果有助于深海油气开采的应用发展，同时为更好研究蜡晶与水合物耦合特性提供可靠的pVT数据。

关键词: 水合物, 相平衡曲线, 诱导时间, 诱导时间变化率