天然气水合物导热性能研究现状

天然气水合物导热系数的研究对于模拟自然界天然气水合物的成藏和天然气水合物勘探、开采具有重要意义。本文介绍了获取天然气水合物导热系数的实验测试和模拟计算方法,分析了气体水合物导热特性、导热机理以及水合物复合体系导热。总结了水合物导热规律,即外界温压条件和晶穴占有率对水合物的导热产生影响,且水合物的导热具有相似的温度压力依赖关系,并呈玻璃体的导热特性。水合物玻璃体导热特性由水合物笼型结构决定,而客体分子的存在强化了水合物导热的玻璃体属性。指出非稳态下天然气水合物导热性能变化研究对分析天然气水合物在常压下的稳定性、确定甲烷水合物等最佳储存温度、从导热角度探讨自保护效应机理等具有重要意义。     

水合物导热系数和热扩散率实验研究

基于Hot Disk热常数分析系统的单面测试功能,建立了一套新的天然气水合物热物性测试系统,并实验研究了I型水合物（甲烷）、H型水合物（甲烷和甲基环己烷）的导热系数和H型水合物的热扩散率。结果显示甲烷水合物样品导热系数随温度的变化非常小,平均导热系数约为0.53 W/(m•K)。结合文献报道和实验分析发现零孔隙率甲烷水合物的导热系数大约为0.7 W/(m•K),水合物样品在压缩过程中虽然减少了孔隙,但是却引起晶体破碎,导致导热系数与理想值差距较大。水合物的导热系数与水合物的类型及客体分子有关,大体顺序为I型 > II型 > H型 > 半笼型水合物。甲烷−甲基环己烷生成的H型水合物热扩散率为0.205 ~ 0.26 mm2/s,和其他类型的水合物相当;水合物的热扩散率大约为水的两倍,而导热系数和水相近。     

压力扰动对甲烷水合物诱导期的影响研究

文章从温度、压力、扰动量和扰动时间点4个方面分别研究了压力扰动对甲烷水合物诱导期的影响.研究结果表明:与静态合成水合物实验相比,不同条件下的压力扰动实验均能大幅度减少诱导时间,诱导时间的波动范围也明显减小,即压力扰动对甲烷水合物合成有稳定的促进效果;在不同温度和压力条件下,降压扰动的促进效果优于增压扰动,而在不同扰动量...     

瞬态热线法测量煤层气水合物导热系数的实验研究

煤层气(瓦斯)的储存和运输是实现煤层气能源利用的重要前提,水合物法是将来煤层气等气体固化储运的主要技术之一。煤层气水合固化储运过程受热量传递的控制,而开展瓦斯水合物的热量传递机理研究,其导热系数是必须要知道的热物性参数。基于瞬态热线法原理,建立了一套测试设备对瓦斯水合物的导热系数进行了实验研究,获得该瓦斯水合物样品导热系数及其和温度的关系。从瓦斯水合物的热物性因素方面支持了以NGH(水合物储运)形式对瓦斯进行水合固化储运的可行性。     

低剂量抑制剂Inhibex501存在下的甲烷水合物相平衡研究

含动力学抑制剂的天然气水合物相平衡研究对新型低剂量抑制剂的开发具有指导作用。在283.6 ~ 290.9 K和7.51 MPa ~ 15.97 MPa的温压范围内研究了抑制剂Inhibex501及其溶剂2-乙二醇单丁醚对甲烷水合物相平衡条件的影响。实验结果显示，0.5wt%和2.0wt%浓度的Inhibex501对甲烷水合物形成的热力学条件具有促进作用，能使甲烷水合物形成移向更高的温度或者更低的压力，而2-乙二醇单丁醚在浓度0.2wt% ~ 1.0wt%范围几乎不改变甲烷水合物形成的热力学条件，N-乙烯基己内酰胺与N-乙烯基吡咯烷酮的共聚物对水合物形成热力学条件的改变起主要作用。     

季盐对气体水合物相平衡影响研究进展

季盐是一种高效的水合物生成添加剂,通常通过填充水合物笼达到改善水合物相平衡条件的效果.季盐对CH4、CO2等气体水合物相平衡条件的影响效果主要与季盐浓度有关.就甲烷水合物而言,同等相平衡压力条件下,TiPeAF和TiAAB对相平衡影响显著:添加了TiPeAF(0.315％)、TiAAB(0.438％)的体系,其相平衡温...     

悬垂水滴与悬浮气泡表面气体水合物形成特性对比

基于悬垂水滴和悬浮气泡表面形成气体水合物的可视化耐高压实验装置,分析探讨了反应压力、温度、水质等因素对水滴和气泡表面气体水合物成核和生长规律的影响.对已有的关于研究单个静止悬垂水滴和悬浮气泡表面气体水合物生长特性的实验现象及结果进行了对比分析,得出结论:温度和压力是影响表面水合物结晶与生长的重要因素;温度的降低或压力的升高均使水合反应速度加快.研究为发展喷雾法和鼓泡法这两种强化制备水合物的方式提供了有效的实验支撑.     

羧甲基纤维素钠对CH4水合物形成过程的影响

羧甲基纤维素钠（CMC-Na）是水基钻井液中的重要组分,为研究CMC-Na对天然气水合物热力学和动力学的影响,实验测量了质量浓度介于0.5% ~ 1.5%的CMC-Na溶液中甲烷水合物的相平衡条件,以及275.2 K、6 MPa的初始条件下CMC-Na溶液中甲烷水合物的形成过程。研究结果表明,CMC-Na对甲烷水合物的热力学稳定性具有微弱的抑制作用,相同压力下相平衡温度降低了0.1 ~ 0.2 K。CMC-Na溶液中形成的甲烷水合物为I型,水合物数为5.84 ~ 5.90。在CMC-Na溶液中,甲烷水合物形成所需的诱导时间大大缩短,表明CMC-Na对甲烷水合物的形成过程具有促进作用。在CMC-Na溶液中水合物生成所需气体消耗量呈阶段式增长。水合物转化率低于35%的情况下,已经生成的水合物没有对搅拌器叶片形成持续附着进而卡住搅拌器。因此,CMC-Na对甲烷水合物的热力学稳定性具有一定的负面影响,对水合物的形成具有一定的促进作用。另外,CMC-Na能够降低水合物生成过程中搅拌扭矩的波动,对维持搅拌的正常运行具有重要作用。     

含水合物地层渗流特性实验研究进展及瞬态压力脉冲法适用性分析

调研了含水合物地层渗流特性实验研究进展,归纳总结了现有的缺点与不足;概述了瞬态压力脉冲法的基本原理及其应用现状,分析讨论了该方法应用于含水合物地层渗流特性实验研究的适用性。主要结论如下：保持稳定渗流难、测量耗时长和水合物易扰动是现有实验研究存在的主要不足;瞬态压力脉冲法能够解决上述不足,且测量精度高,具有良好的适用性,特别适用于我国南海含水合物地层。建议开展我国南海水合物成藏与开采过程中地层渗流特性模拟实验研究工作。     

四丁基氯化铵半笼型水合物的相平衡模型

本文在范德瓦尔?普朗特理论的基础上,考虑了四丁基氯化铵（TBAC）水合物的结构特征,建立了TBAC半笼型水合物相平衡模型。模型确定了水在空水合物晶格的蒸汽压及兰格缪尔常数与TBAC浓度的关系,引用e-NRTL模型和PR气体状态方程分别计算液相组分活度系数和客体分子气相逸度。同时,本文在280.1 K ~ 293.6 K温度范围和0.337 MPa ~ 7.017 MPa压力范围内预测了TBAC质量浓度范围为4.34% ~ 34%的溶液体系下TBAC + CH₄、TBAC + CO₂半笼型水合物的相平衡条件,预测压力与实验数据的平均绝对偏差分别为3.2637% 和9.2258%。预测结果与实验数据吻合较好。     

Modeling the mechanical response of gas hydrate reservoirs in triaxial stress space

Exploitation of gas from deep-sea methane hydrate-bearing layers might lead to some geological disasters, including marine landslides and excessive settlement of marine ground. The first offshore gas production tests for methane hydrate-bearing sediments were carried out in eastern Nankai Trough. However, knowledge on mechanical behavior of gas hydrate reservoirs with similar gradation and minerology component to the marine sediment is still insufficient. Consequently, proper modeling of geomechanical properties of methane hydrate-bearing sediments is crucial for reservoir simulation and deep ocean ground stability analysis for long-term gas production in the future. This study conducted a series of triaxial shear tests to examine the shear response of methane hydrate-bearing sediments with a similar grading curve and minerology components to the hydrate-rich sediments in Nankai Trough. The test results demonstrated that the presence of hydrate mass between sand grains altered the stress-strain pattern from strain-hardening to postpeak strain-softening. A simple constitutive model based on several empirical relationships of granular materials is proposed to describe the stress-strain relationship of methane hydrate-bearing sediments under triaxial stress condition. This model can reproduce the enhancement of shear strength, initial stiffness, and dilation behavior of methane hydrate-bearing sediments containing different amounts of fines content with a rise in the methane hydrate saturation at a wide range of effective confining pressures. The numerical results indicate that the parameter A associated with initial stiffness of stress-strain curve and the parameter $\text{α}$ related with dilation properties are jointly governed by the confining pressure, fines content, and hydrate saturation.     

Shear strength and pore pressure characteristics of methane hydrate-bearing soil under undrained condition

Hydrate exploitation requires a deep understanding on the mechanical behavior of methane hydrate-bearing sediment (MHBS). Due to the low permeability of overlying strata, partial MHBS likely exhibit failure behavior under undrained condition. Therefore, it is essential to understand the undrained shear strength and excess pore pressure behavior of MHBS for facilitating the evaluation of the stability of hydrate-bearing layer during methane hydrate recovery. This study conducted several undrained triaxial compression and hydrate dissociation tests on methane hydrate-bearing sand specimen to analyze the shear strength and excess pore pressure characteristics of MHBS under undrained condition. The experimental result shows that hydrate saturation and initial effective confining pressure significantly affect the undrained mechanical behavior of MHBS. Hydrate saturation increases the shear strength and negative excess pore pressure. High initial effective confining pressure also enhances the shear strength but suppressed the negative excess pore pressure. Hydrate saturation has a minimal effect on the undrained internal friction angle but remarkably enhances the undrained cohesion. The effective internal friction angle and cohesion exhibits an increase with the increase in hydrate saturation. Notably, completely different from the common soil, the effective undrained strength indexes are not equivalent to the drained strength indexes for MHBS, which should be careful in evaluating the stability of methane hydrate-bearing layer. In addition, the hydrate dissociation test by thermal stimulation method concludes that hydrate dissociation induces the positive excess pore pressure, axial compression, and volume expansion under undrained condition. The large deviatoric stress enhances volume expansion of MHBS but hinders the generation in excess pore pressure during hydrate dissociation. These findings significantly contribute to the safe exploitation process of methane hydrate.     

Analysis of physical properties of gas hydrate-bearing unconsolidated sediment samples from the ultra-deepwater area in the South China Sea

Marine natural gas hydrate has recently attracted global attention as a potential new clean energy source. Laboratory measurements of various physical properties of gas hydrate-bearing marine sediments can provide valuable information for developing efficient and safe extraction technology of natural gas hydrates. This study presents comprehensive measurement results and analysis of drilled hydrate-bearing sediments samples recovered from Qiongdongnan Basin in the South China Sea. The results show that the gas hydrate in the core samples is mainly methane hydrate with a methane content of approximately 95%, and the other components are ethane and carbon dioxide. The saturation of the samples fluctuates from 2%–60%, the porosity is approximately 38%–43%, and the water content is approximately 30%–50%, which indicate that high water saturation means that timely drainage should be paid attention to during hydrate extraction. In addition, the median diameter of the sediment samples is mainly distributed in the range of 15 to 34 μm, and attention should be paid to the prevention and control of sand production in the mining process. Moreover, the thermal conductivity is distributed in the range of 0.75 to 0.96 W/(m∙K) as measured by the flat plate heat source method. The relatively low thermal conductivity of hydrates at this study site indicates that a combined approach is encouraged for natural gas production technologies. It is also found that clay flakes and fine particles are attached to the surface of large particles in large numbers. Such characteristics will lead to insufficient permeability during the production process.     

天然气水合物沉积物分解过程中本构关系研究

天然气水合物具有储量大、分布广泛、清洁燃烧等优点,近年来受到研究人员的广泛关注。为了实现天然气水合物资源的安全高效开采,对其沉积层的力学稳定性进行系统评估是十分必要的。本研究在实验室内重塑了40%孔隙度的天然气水合物沉积物试样,并基于力学实验设备,对其在不同围压条件下分解过程中的力学强度及变形进行了一系列测试,获取了相应的应力应变数据。研究结果表明,水合物分解会造成沉积层强度的降低。此外,基于实验数据,在借鉴土力学邓肯-张本构模型的基础上,考虑了围压及分解时间对沉积物力学特性的影响,本文构建了适用于不同围压条件下天然气水合物沉积物分解过程中的本构模型,研究结果表明,该模型可以较好地模拟沉积物试样在分解过程中的应力应变关系,可为实现天然气水合物的安全开采提供一定的理论依据。     

Study on the non-in situ measurement method for hydrate thermal conductivity

A non-in situ measurement method for gas hydrate thermal conductivity was established, including the sample preparation, sample transfer, sample loading, and thermal conductivity measurement. Taking tetrahydrofuran (THF) hydrate and methane hydrate as examples, the detailed process was investigated by many experiments. THF hydrate samples were prepared by the combined method of THF aqueous solution + temperature oscillation + aging, while methane hydrate samples were prepared by the combined method of compacted ice powder + temperature oscillation + supplementary gas + aging. The sample box, quick-opening reactor, and sample mold were developed to improve the sample quality, shorten preparation time, and reduce exposure time. It was found that the time of sample transfer and loading can be controlled within 1 minute and 15 minutes for THF hydrate and methane hydrate, respectively. The thermal conductivities of THF hydrate and methane hydrate are 0.5200 ~ 0.5700 and 0.4803 ~ 0.6197 W•m⁻¹•K⁻¹ in the studied temperature range, respectively. The thermal conductivity of THF hydrate shows a positive dependence on temperature. The thermal conductivity of methane hydrate shows no dependence on temperature, but negative dependence on pressure. The errors of THF hydrate mainly come from the frost layer and micro airflow while the errors of methane hydrate mainly come from the ice film and micro gas flow. The precision, accuracy, and uncertainty of THF hydrate are 0.09% ~ 0.75%, 0.0450 ~ 0.0650 W•m⁻¹•K⁻¹ (absolute difference), 8.65% ~ 12.01% (relative error) and 0.00007 ~ 0.00017, respectively. Similarly, the precision, accuracy and uncertainty of methane hydrate are 0.04% ~ 5.98%, 0.005 ~ 0.0619 W•m⁻¹•K⁻¹(absolute difference), 1.02% ~ 12.12% (relative error) and 0.00016 ~ 0.00032, respectively. Based on the analysis, the established non-in situ measurement technique in this work is completely feasible and can be used to measure the obtained naturally occurring samples.     

基于TDR双参数的沉积物中水合物饱和度测量

针对沉积物中水合物饱和度的测量问题,立足于时域反射技术（TDR）能够同时获得含水合物沉积物表观介电常数和电导率的优点,提出了一种基于介电常数/电导率双参数的水合物饱和度评价新方法。在分析介电常数和电导率测量原理的基础上,设计了四氢呋喃（THF）水合物模拟实验与参数测量系统以及实验方案;基于TDR测量响应分析了孔隙水电导率对水饱和的以及含水合物的模拟沉积物介电常数和电导率的影响;利用TDR获取的不同水合物饱和度条件下的介电常数测量数据对比分析了经典介电常数模型的性能,并以Lichteneker-Rother（LR）模型为原型建立了水合物饱和度与介电常数之间的关系模型,以阿尔奇公式为原型建立了基于TDR测量电导率的水合物饱和度计算模型。研究结果表明：采用LR模型和Maxwell-DeLoor模型能够较准确地描述TDR测量表观介电常数与水合物饱和度之间的关系;基于表观介电常数/电导率双参数的水合物饱和度联合评价方法为提高评价结果的准确度和可靠性提供了新途径。将来需要结合水合物储层实际特征开展模拟实验并进一步完善饱和度计算模型,将基于TDR双参数的饱和度联合评价方法推广应用到含天然气水合物沉积物。     

Enhancement of methane hydrate formation using a mixture of tetrahydrofuran and oxidized multi‐wall carbon nanotubes

Methane hydrate is a kind of gas hydrate formed by physical binding between water molecules and methane gas, which is captured in the cavities of water molecules under a specific temperature and pressure. Pure methane hydrate of 1 m³ can be decomposed into methane gas of 172 m³ and water of 0.8 m³ at standard conditions. Methane hydrate has many practical applications such as separation processes, natural gas storage transportation, and carbon dioxide sequestration. For the industrial utilization of this substance, it is essential to find a rapid method of manufacturing it. This work studies the formation of methane hydrates by using tetrahydrofuran (THF) and oxidized carbon nanotubes (OMWCNTs) by testing different fluid mixtures of THF and carbon nanotubes. The results show that when the mixed fluid contained THF, the OMWCNTs showed the gas consumption 5.2 times that of distilled water at 3.4 K subcooling. Also, THF's effects as a thermodynamic phase equilibrium promoter were preserved when it was used with OMWCNTs. Therefore, it can be expected that when OMWCNTs are used with an aqueous mixture of THF, both the favorable phase equilibrium of THF and the high gas consumption of the carbon nanotubes can be obtained. Copyright © 2013 John Wiley & Sons, Ltd.     

Gas production from different classes of methane hydrate deposits by the depressurization method

There are four primary classes of natural gas hydrate deposits in natural world. The differences between them are in the distribution of the methane hydrate, free gas, and free water layers. A reactor which the height was 120 mm and the inner diameter was 103 mm was used in hydrate formation and dissociation, and 17 thermocouples measured the distribution of temperature during the mining process. Different experimental means were applied to simulate three classes of methane hydrate deposits, in which water and glass beads filled in different orders. The hydrate samples were dissociated by depressurization, and the results showed no need to test a backpressure greater than 94% of the equilibrium pressure of methane hydrate. Class 1 sample's methane hydrate decomposition rate was slower than that of class 3 sample at the beginning of depressurization when backpressure was 2.3 and 2.6 MPa, but then, the opposite happened. The average dissociation rate decreased nearly linearly with the increase in backpressure for the class 1 samples.     

Compressional wave velocity of hydrate-bearing bentheimer sediments with varying pore fillings

A potential alternative energy resource to meet energy demands is the vast amount of gas stored in hydrate reserves. However, major challenges in terms of exploration and production surround profitable and effective exploitation of these reserves. The measurement of acoustic velocity is a useful method for exploration of gas hydrate reserves and can be an efficient method to characterize the hydrate-bearing sediments. In this study, the compressional wave velocity (P-wave velocity) of consolidated sediments (Bentheimer) with and without tetrahydrofuran hydrate-bearing pore fillings were measured using the pulse transmission method. The study has found that the P-wave velocity of consolidated sediments increase with increasing hydrate formation and confining pressure. Of the two samples tested, the increase in wave velocity of the dry and hydrate-bearing samples amounted to 27.6% and 31.9%, respectively. Interestingly, at the initial stage of hydrate formation, there was no change in P-wave velocity, which was followed by a steady increase as the hydrate crystals began to agglomerate and then it increased rapidly to a constant value, suggesting that the test solution had converted to a hydrate solid.