苏丹红7B染色剂对水合物生成分解动力学的影响

基于高压反应釜装置进行了一系列不同初始压力、不同过冷度条件下,添加染色剂/不加染色剂的水合物生成与分解实验,通过分析实验过程中体系压力、温度随时间的变化,研究了苏丹红7B染色剂对水合物生成结晶诱导期、水合物生成体积分数及气体消耗率的影响.结果表明:苏丹红7B对水合物生成与分解的动力学的影响,在不同的实验条件下,表现不一;在高过饱和度下,苏丹红7B对水合物生成与分解动力学的影响会减弱;在过冷度较高时,苏丹红7B对水合物生成与分解动力学表现出较大的影响,一方面促进水合物结晶诱导,另一方面又抑制水合物生长,还对水合物分解时间有延长的作用.经深入剖析油溶性染色剂苏丹红7B分子会随温度变化的溶解与析出,与乳化剂协同吸附或脱附,进而影响水合物生成/分解动力学的传质及颗粒行为.总之,本研究论证了在引入染色剂研究水合物生成分解规律时,应该优选对水合物动力学生成及分解没有影响或影响较少的染色剂物质.     

甲烷水合物生成分解的实验研究

海底存在着大量可燃冰,1 m3可燃冰能够储存160 m3的天然气。因此,可燃冰的开采与利用可燃冰储存与运输天然气具有重要意义。在改变搅拌、过冷度及低浓度动力学抑制剂的条件下,对甲烷水合物生成量与生成速率进行了实验研究。将甲烷水合物进行升温分解,分析水合物分解时的压力变化情况。结果表明:搅拌对甲烷水合物生成的促进效果最好,其次是过冷度,最后是超低浓度动力学抑制剂;水合物生成的传质过程最终被阻碍,采取将水与天然气的上下位置交换的方法,可以生成更多水合物。水合物升温可以得到相平衡曲线;改变初始时刻压力,可以得到不同温度区间的相平衡曲线;降低水合物分解时的升温速度,可以得到更长温度区间的相平衡曲线。     

油水体系内水合物的生成:温度、压力和搅拌速率影响

水合物在管道内的生成对流动安全保障构成了极大威胁。为研究水合物在油水体系内的生成特性,本文以天然气、柴油、水为实验介质,在高压可视反应釜内开展了一系列不同温度、压力和搅拌速率的水合物生成实验。根据测试实验中温度、压力的变化趋势,首先分析了两种不同实验步骤下水合物的生成过程。然后,基于从反应釜可视窗处观察到的实验现象,研究了温度、压力和搅拌速率对水合物生成和分布位置、水合物生成形态及水合物形态演化过程的影响。实验中,可以观察到水合物的聚集、沉积和壁面膜生长现象。同时,实验还研究了温度、压力和搅拌转速对诱导时间、壁面水合物膜生长速率及气体消耗速率等水合物生成动力学参数的影响。本文研究成果可为油气管道水合物防治技术的发展提供理论支持。     

一种低剂量水合物动力学抑制剂的研发

为了更好地评价所开发的水合物动力学抑制剂的性能,利用模拟的崖城气体对其抑制效果进行了室内评价。结果表明,质量分数为1.0%的动力学抑制剂可有效延长水合物的生成诱导期。利用海上东方1-1气田现场物流对其进行评价,结果表明,该体系中质量分数为3.0%的动力学抑制剂可以有效抑制水合物的生成。最后实施了油气田现场应用试验,结果表明,很少量的该动力学抑制剂即可有效保证生产管线的平稳运行。3种不同程度的评估结果均充分验证了所开发的水合物动力学抑制剂的抑制效果。     

天然气水合物生成与相平衡曲线的试验分析

通过改变动力学抑制剂、过冷度、搅拌,借助生成实验装置,分析天然气水合物的生成效果,比较以上三个条件下的天然气水合物的生成速度和生成量,进而得出以上三个变量的对天然气水合物生成效果的贡献。结果表明:增加搅拌在天然气水合物生成过程中起主要作用,其次是过冷度以及动力学抑制剂。通过对水合物生成以及分解过程中压力-温度曲线的拟合,放缓反应釜内温度的升幅,可以得到更长更精确的拟合曲线。     

含砂搅拌体系甲烷水合物生成与分解实验研究

利用高压反应釜装置,在不同初始压力、砂粒粒径等条件下进行甲烷水合物的生成与分解实验,研究细质砂粒固相颗粒对甲烷水合物成核诱导时间、生成和分解等的影响规律。结果表明:砂粒能够促进甲烷水合物生长,体系初始压力越高,水合物生成速率越高;体系初始压力为7.2 MPa、砂粒粒径为2 000目(6.5μm)时,水合物生成过程最稳定,且水合物生成量最多;在分解过程中,纯水体系和含砂体系的分解速率相当,只存在气体释放量的差异。进而得出结论:砂粒固体颗粒的存在会促进水合物生成,所以在水合物开采过程中,若工况满足水合物生成条件,水合物二次生成会更易发生,使得矿藏砂粒、水合物、天然气、海水在管道内的多相混输堵塞风险增加;含砂条件对水合物分解的影响作用不大,矿砂在水合物分解过程中对流动安全的影响有待深入研究。该研究成果为解决深水浅层水合物开采过程中的流动安全保障问题,提供了重要的理论基础和技术支撑。     

水合冷冻法海水淡化研究

试验研究了HCFC-141b在含盐溶液中的水合和分解过程,测定了水合物分解后的盐度变化.结果表明,HCFC-141b在盐水中生成水合物的过程中,盐水的浓度对水合物生成的过冷度有一定影响,浓度太低或太高都对过冷度影响不大,1.0%的氯化钠可以有效减小过冷度.测量水合物分解后的水溶液发现盐度显著降低,用水合物的生成和分解可以达到海水淡化的目的.根据水合物的特点设计了水合物法海水淡化的试验装置,筛选了适用于该方法的水合物工质,其中乙烷为最好的水合物法海水淡化工质.通过计算发现加大气体流量、提高充气压力和改善生成条件可提高淡水产率,当50%的气体参加水合反应则淡水产率可提高到1.25 L·min-1.     

纤维素纳米晶对甲烷水合物生成影响

油气管道输送过程中水合物的防治已成为流动安全保障技术的关键课题。文中研究了纳米晶纤维素(CNC)对甲烷气体水化浆体宏观结构的影响,测量了在5 MPa的初始压力和274.2 K的初始温度下,10 h内的动力学参数的变化。将水合物聚结现象与生成机理结合,对新生成水合物浆液进行动力学分析,同时从化学结构的角度研究了相变体系出现孔隙结构的变化。结果表明,在0.1%—0.3%质量分数范围内,颗粒质量分数每升高0.1%,诱导时间分别延长了17 min和74 min,最高延长了188%。CNC存在时,水合物浆体内存在大量球状孔隙,使Ⅰ型水合物的生成具有网状结构。这些变化与反应时间内测量的诱导时间变化相对应。     

水合物生成和分解动力学研究现状

从微观动力学和宏观动力学的角度对水合物生成和分解动力学研究文献进行了分类、评述,着重点是水合物生成的微观机理和水合物晶体生长的宏观动力学.关于水合物生成的微观动力学,着重介绍3个比较完整的水合物生成机理以及相应的机理模型.关于水合物生成的宏观动力学,着重阐述加拿大Bishnoi实验室所取得的研究成果以及日本学者结合CO_2水合物处置法开展的CO_2水合物生成动力学研究工作.关于水合物分解,主要讨论水合物在受热、降压和抑制剂存在时的分解动力学.基于水合物生成和分解动力学的研究现状,指出了今后研究的8个重要方向.     

水合物动力学抑制剂室内实验及现场应用

在天然气开采及储运中、水合物导致阀门阻塞、气井停产、管道停输等严重事故。为了满足低耗、高效、环保等要求,本文对四种水合物动力学抑制剂进行了不同浓度下的抗冻性性能评价以及不同浓度、不同过冷度下抑制剂流动实验研究,结果表明在抗冻数据可知,随着抑制剂浓度的增加,抑制剂溶液的抗冻温度点逐渐降低;并且在相同浓度下的抗冻效果VC-713抑制剂最好,1^#抑制剂次之,PVP抑制剂溶液最差。不同浓度、不同过冷度下抑制剂流动实验中,在0℃上下的环境温度,浓度在1%～2%之间的这四种水合物抑制剂是可以起到抑制效果的;并且在此浓度范围内的这四种抑制剂,其浓度对水合物抑制效果影响不大。2.0%的四种抑制剂在过冷度均小于15℃,即环境温度在-5℃以上时,可以起到抑制水合物生成的作用,而环境温度在-5～-25℃时,这四种抑制剂都起不到抑制效果;VC-713抑制剂作用最好,1#抑制剂次之,PVP抑制剂溶液最差。不同浓度、不同过冷度下抑制剂流动实验中,在0℃上下的环境温度,浓度在1%～2%之间的这四种水合物抑制剂是可以起到抑制效果的;并且在此浓度范围内的这四种抑制剂,其浓度对水合物抑制效果影响不大。2.0%的四种抑制剂在过冷度均小于15℃,即环境温度在-5℃以上时,可以起到抑制水合物生成的作用,而环境温度在-5～-25℃时,这四种抑制剂都起不到抑制效果;VC-713抑制剂作用最好,1^#抑制剂作用次之,PVP抑制剂作用最差。并在苏里格井区中一口井进行了现场试验,效果明显。     

Synthesis and evaluation of poly (N-vinyl caprolactam)-co-tert-butyl acrylate as kinetic hydrate inhibitor

Low dosage kinetic hydrate inhibitors(KHIs) are a kind of alternative chemical additives to high dosage thermodynamic inhibitors for preventing gas hydrate formation in oil & gas production wells and transportation pipelines.In this paper,a new KHI,poly(N-vinyl caprolactam)-co-tert-butyl acrylate(PVCapco-TBA),was successfully synthesized with N-vinyl caprolactam(NVCap) and tert-butyl acrylate.The kinetic inhibition performances of PVCap-co-TBA on the formations of both structure Ⅰ methane hy...     

The gas-adsorption mechanism of kinetic hydrate inhibitors

Molecular dynamics was employed to study the inhibition mechanism of vinyl lactam-based kinetic hydrate inhibitors (KHIs). By comparing the inhibition functions of the same KHIs at different initial locations, we found that the KHI molecules on the surface of hydrate nuclei could obviously prolong the hydrate induction time and exhibited the best inhibition effect. The impacts of KHIs on the methane migration and the arrangement of H₂O molecules were analyzed at the molecular level. A gas-adsorbing mechanism for KHIs (i.e., the KHIs with an excellent gas adsorption ability could reduce the supersaturation of methane in the aqueous solution, reinforce the migration resistance of methane to the nucleus, and further inhibit the hydrate growth) was proposed. In addition, the conformations of KHI polymer molecules in the aqueous solution are closely related to their inhibitory effect, that is, stretched skeletons and well-organized structures would maximize their inhibitory effect.     

Tetrahydrofuran hydrate crystal growth inhibition by hyperbranched poly(ester amide)s

Kinetic hydrate inhibitors (KHIs) are water-soluble polymers designed to delay gas hydrate formation in gas and oilfield operations. Inhibition of growth of gas hydrate crystals is one of the mechanisms by which KHIs have been proposed to act. One class of commercial KHIs is the hyperbranched poly(ester amide)s. We have investigated the ability of a range of structurally different hyperbranched poly(ester amide)s to inhibit the crystal growth of tetrahydrofuran (THF) hydrate which forms a Structure II clathrate hydrate, the most common gas hydrate structure encountered in the upstream oil and gas industry. The results indicate that there is an optimum size of hydrophobic groups attached to the succinyl part of the polymer, which gives best crystal growth inhibition. However, total inhibition was impossible to achieve even at a concentration of 8000 ppm of one of the best polymers at a subcooling of 3.4 °C, tentatively suggesting that polymer adsorption onto natural gas hydrate crystal surfaces is probably not the primary mechanism of kinetic inhibition operating in field applications with this class of KHI.     

An investigation into the laboratory method for the evaluation of the performance of kinetic hydrate inhibitors using superheated gas hydrates

Kinetic hydrate inhibitors (KHIs) are used to prevent gas hydrate formation in gas and oilfield operations. Recently, a new KHI test method was reported in which hydrates are formed and re-melted just above the equilibrium temperature, before the fluids are re-cooled and the performance of the chemical as a KHI is determined. The method, which we have called the superheated hydrate test method, is claimed to be more reliable for KHI ranking in small equipment, giving less scattering in the hold time data due to avoiding the stochastic nature of the first hydrate formation. We have independently investigated this superheated hydrate test method in steel and sapphire autoclave tests using a gas mixture forming Structure II hydrates and a liquid hydrocarbon phase, which was necessary for satisfactory results. Our results indicate that hold times are shorter than using non-superheated hydrate test methods, but they are more reproducible with less scattering. The reduced scattering occurs in isothermal or slow ramping experiments even when the hydrates are melted at more than 10 °C above the equilibrium temperature (T_eq). However, if a rapid cooling method is used, the improved reproducibility is retained when melting hydrate at 2.4 °C above T_eq but lost when warming to 8.4 °C above T_eq. Using the ramping test method, most, but not all the KHIs tested agreed with the same performance ranking obtained using traditional non-superheated hydrate test methods. This may be related to the variation in the dissociation temperature of gas hydrates with different KHIs and different KHI inhibition mechanisms. Results also varied between different size autoclave equipments.     

Reviews of gas hydrate inhibitors in gas-dominant pipelines and application of kinetic hydrate inhibitors in China

During the development and application of natural gas, hydrate plugging the pipelines is a very important issue to solve. Currently, adding thermodynamic hydrate inhibitors (THIs) and kinetic hydrate inhibitors (KHIs) in gas-dominated pipelines is a main way to prevent hydrate plugging of flow lines. This paper mainly reviews the efforts to develop THIs and KHIs in the past 20 years, compare the role of various THIs, such as methanol, ethylene glycol and electrolyte, and give the tips in using. The direction of KHIs is toward high efficiency, low toxicity, low pollution and low cost. More than a hundred inhibitors, including polymers, natural products and ionic liquids, have been synthesized in the past decade. Some of them have better performance than the current commercial KHIs. However, there are still few problems, such as the complex synthesis process, high cost and low solubility, impeding the commercialization of these inhibitors. The review also summarized some application of KHIs in China. Research of KHIs in China began late. There are no KHIs used in gas pipelines. Only a few field tests have been carried out. In the end of this paper, the field test of self-developed KHIs by China is summarized, and the guidance is given according to the application results.     

Experimental and density functional theory computational evaluation of poly(N-vinyl caprolactam-co-butyl methacrylate) kinetic hydrate inhibitors

Natural gas hydrate inhibitor has been serving the oil and gas industry for many years. The development and search for new inhibitors remain the focus of research. In this study, the solution polymerization method was employed to prepare poly(N-vinyl caprolactam-co-butyl methacrylate) (P(VCap-BMA)), as a new kinetic hydrate inhibitor (KHI). The inhibition properties of P(VCap-BMA) were investigated by tetrahydrofuran (THF) hydrate testing and natural gas hydrate forming and compared with the commercial KHIs. The experiment showed that PVCap performed better than copolymer P(VCap-BMA). However, low doses of methanol or ethylene glycol are compounded with KHIs. The compounding inhibitors show a synergistic inhibitory effect. More interesting is the P(VCap-BMA)-methanol system has a better inhibitory effect than the PVCap-methanol system. 1% P(VCap-BMA) + 5% methanol presented the best inhibiting performance at subcooling 10.3 ℃, the induction time of natural gas hydrate was 445 min. Finally, the interaction between water and several dimeric inhibitors compared by natural bond orbital (NBO) analyses and density functional theory (DFT) indicated that inhibitor molecules were able to form the hydrogen bond with the water molecules, which result in gas hydrate inhibition. These exciting properties make the P(VCap-BMA) compound hydrate inhibitor promising candidates for numerous applications in the petrochemical industry.     

Effect of complex inhibitors containing ionic liquids and PVP K90 on formation of methane hydrate

Injecting inhibitors is the most commonly used method in the oil and gas industry to solve the problem of blockage caused by hydrate formation during pipeline transportation. However, most of the kinetic hydrate inhibitors (KHIs) are strictly limited by weak inhibition performance and low subcooling. Ionic liquids, a kind of green solvent, have been recognized to act as excellent thermodynamic inhibitors on methane hydrate formation. So, it is proposed to add the ionic liquids into KHIs to improve their overall performance. In this paper, the kinetic effects of an ionic liquid N-butyl-N-methylpyrrolidine tetrafluoroborate ([BMP][BF₄]), a commercial kinetic inhibitor polyvinyl pyrrolidone (PVP K90) and their mixtures with different mass ratios on the methane hydrate formation were experimentally studied at 8.0 K subcooling and two concentrations [1.0%(mass) and 2.0%(mass)]. The best mass ratio of the compound inhibitor was determined. Moreover, the crystal structures and cage occupancy characteristics of methane hydrates formed without and with inhibitors at different mass concentrations and composition ratios were measured by using powder X-ray diffraction (PXRD) and low-temperature Laser Raman spectrometers. It was found that the addition of inhibitors did not change the crystal structure of methane hydrate, but affected the cage occupancies and hydration numbers. Based on the results from macroscopic kinetics and microscopic structure tests, the inhibition mechanism of compound inhibitors was proposed.     

离子液体与PVP K90复合抑制剂对甲烷水合物的生成影响

注入抑制剂是油气行业解决管道输送过程因水合物生成而引发的堵塞问题最常用的方法。但现有大多数动力学抑制剂（KHIs）存在抑制性能不足、高过冷度条件下会失效等问题，可应用场合大大受限。离子液体作为绿色溶剂对甲烷水合物具有良好的热力学抑制作用。为改进KHIs的性能，提出将离子液体与KHIs复合。本文实验考察8.0 K过冷度、两种浓度下[1.0%(质量)、2.0%(质量)]离子液体N-丁基-N-甲基吡咯烷四氟硼酸盐([BMP][BF₄])、聚乙烯基吡咯烷酮（PVP K90）以及二者复配构成的复合型抑制剂对甲烷水合物抑制规律，得到了最佳组分配比。利用粉末X射线衍射（PXRD）和低温激光拉曼光谱测量了不同抑制剂体系中形成的甲烷水合物晶体微观结构和晶穴占有率，发现添加抑制剂不会改变sI型甲烷水合物晶体结构，但会影响水合物晶体的大、小笼占有率和水合数。结合宏观动力学实验和微观结构测试结果，揭示离子液体与PVP K90复合抑制剂的抑制机理。     

Dual function inhibitors for methane hydrate

The performance of five imidazolium-based ionic liquids as a new class of gas hydrate inhibitors has been investigated. Their effects on the equilibrium hydrate dissociation curve in a pressure range of 30-110 bar and the induction time of hydrate formation at 114 bar and a high degree of supercooling, i.e., about 25 °C, are measured in a high-pressure micro differential scanning calorimeter. It is found that these ionic liquids, due to their strong electrostatic charges and hydrogen bond with water, could shift the equilibrium hydrate dissociation/stability curve to a lower temperature and, at the same time, retard the hydrate formation by slowing down the hydrate nucleation rate, thus are able to act as both thermodynamic and kinetic inhibitors. This dual function is expected to make this type of inhibitors perform more effectively than the existing inhibitors.     

气体水合物抑制剂的研制与性能评价

针对海洋深水钻井过程中气体水合物的形成严重影响钻井作业的顺利进行等问题,室内经过大量的优选实验,采用甲基丙烯酸乙酯和N-乙烯基吡咯烷酮作为单体,并对单体比例、引发剂、反应温度及反应时间等综合因素进行分析,研制出低剂量气体水合物抑制剂HLA。通过四氢呋喃(THF)测试法和水合物生成模拟实验装置评价其效果,实验结果表明:盐类气体水合物抑制剂能使形成气体水合物的温度和压力条件得到改变,此外还可以有效的抑制气体水合物的形成;低剂量气体水合物抑制剂HLA能使水合物的形成速率得到有效降低,使形成水合物晶核的诱导时间得到一定的延长,使晶体的聚集过程得到一定的改变,但并不能从实际上改变气体水合物形成的相平衡。