含下伏气沉积层内水合物相变与产气特性

含下伏气的水合物沉积层被认为是最具开采潜力的水合物储层类型。本文利用岩心夹持器在恒定围压9 MPa下,研究了连通不同压力下伏气的南海沉积物内天然气水合物生成、分解及产气特征。研究结果表明,水合物饱和度与下伏气初始压力(7.2～8.1 MPa)呈非线性正比关系,而在8.1～8.4 MPa内两者呈负相关。同时,发现在降压开采过程中下伏气为水合物分解提供热量,促进了水合物分解,提高了水合物平均分解速率。此外,下伏气有助于缓解压降速率,从而有效减轻有效应力对水合物沉积层的破坏。下伏气作为开采产气的重要供气源,能提高气体回收率。本文研究结论将为今后降压开采含下伏气的水合物提供一定的理论指导。     

基于网络热力学的热力系统能量流描述

网络热力学起源于热力系统分析,但其广泛应用却是在生命系统等非热系统领域,这是因为网络热力学方法需要从能量的角度分析系统,而热力系统中的热量在输运过程中具有物质属性,因此必须有新的能量形式。若将热量视作"流",而将温度视为"力",那么流与力的乘积就为(火积)流。(火积)具有能量的内涵,(火积)流就可以被视为热力系统的能量流。并且,在能量输运过程中,其他形式的能量如功量也可以视为一种物质。由此,在(火积)流的统一视角下,各种形式的能量在网络中便可得到有机结合。分析结果表明,对于换热系统以及热力系统,基于网络热力学的能量流法也可以表达系统的物理本质。在(火积)流的视角下,能量流键图可以很好地反映热力系统的拓扑结构。例如对于热机-热泵供热联合循环,热机与热泵之间的功量交换过程即使是可逆过程,也会存在(火积)的损失或产生,这从能量流键图中可以被直观地刻画出来。     

热采井注蒸汽与注多元热流体井筒流动与传热对比分析

针对海上稠油开采出现的问题,国内发展了注多元热流体吞吐热力采油技术。与蒸汽热力采油相比,多元热流体可以显著降低稠油黏度、增加油层压力,提高开采效率。本文基于实际气体状态方程和混合法则建立注多元热流体内部流动与传热模型,并与注蒸汽井筒流动与传热状态进行对比,详细对比两种热采介质在井筒流动与传热情况。通过研究发现:在井筒注入相同温度与相同注入速率的多元热流体与饱和蒸汽,多元热流体井筒压力和温度下降速度更快,到达井底时压力更大,温度更低,与地层和油层的温差更小,井筒热损失更少,但是热量含量低,油层加热范围小。要想达到与蒸汽一样加热效果,可以增加多元热流体注入速率和注入温度。同时由于CO_2和N_2作用,油层温度分布更加均匀,热量更多,油层加热范围更大,注多元热流体开采效果更好。     

新型微燃机分布式冷热电联供系统热力性能分析

本文提出了一种新型微型燃气轮机分布式冷热电联供系统,集成了微型燃气轮机、氨水Rankine循环,单双效复合溴化锂吸收式制冷机,烟气热水换热器。氨水Rankine循环中,混合工质升温蒸发过程回收微燃机烟气余热,降温冷凝过程热量用于驱动吸收式制冷机。研究了新系统的热力性能、与没有集成氨水Rankine循环的典型微燃机分布式冷热电系统进行了对比分析,并对关键过程进行了能量品位(EUD)分析。热力性能结果表明,集成了氨水Rankine循环的新型系统热力性能优异,相对节能率为22.41%,(?)效率为31.64%,新系统可以在不影响系统相对节能率的前提下调整系统的冷负荷(35.6~51 kW)。能量品位分析表明,新系统性能提升的原因在于新系统氨水Rankine循环的吸热、放热过程与冷热源的能量品位差减小。     

高效太阳能热发电系统性能分析

为了提高太阳能热发电站的发电效率,提出了耦合空气轮机、汽轮机及热力塔为一体的太阳能发电系统。在该系统中,吸热器吸收的太阳能加热压气机所压缩的高压空气,多余的热量被储存在储热装置中以在无阳光的时候维持电站正常运转。被加热后的高压空气驱动透平后排入余热锅炉产生蒸汽驱动汽轮机,余热锅炉的排气以及冷却汽轮机凝汽器的空气进入热力塔底部驱动风力涡轮。本文建立了该系统的热力学模型并对系统效率作了计算,计算中对水蒸汽动力循环的参数做了优化。计算结果表明,该系统相比传统的太阳能热电站发电效率明显提高,在环境温度为15℃、空气轮机组透平进口温度为700℃、热力塔高度400 m以上时,空气轮机工作在有回热热效率高的工作模式下,系统循环效率超过了50%,该太阳能电站总的能量转换效率将可达到33%。     

钕玻璃宽带激光放大能量提取效率研究

基于钕玻璃宽带脉冲激光放大模型,采用数值模拟的方法,研究了钕玻璃放大器对不同输入光通量、不同脉宽以及不同带宽(或波长分布)脉冲激光放大的能量提取效率。计算结果表明,钕玻璃宽带放大能量提取效率随着输入光通量的增加而提高,并最终趋于某一定值。对于以均匀加宽为主的介质,随着带宽的增加,能量提取效率逐渐下降;对于以非均匀加宽为主的介质,随着带宽的增加,能量提取效率先逐渐升高,达到最大值后开始下降。对于均匀加宽与非均匀加宽线宽比为0.1的混合加宽介质,在饱和通量输入条件下,使用宽带激光能够带来大约80%的效率提升。     

CO_2置换CH_4水合物实验研究进展

全面总结了目前CO2置换CH4水合物中CH4实验研究进展。首先从水合物结构角度出发讨论置换的可能性及置换效率;而后分别从热力学和动力学角度探讨置换反应机理;最后设计并优化了实验系统。作者认为探明置换内在机理是未来置换法开采水合物能源技术发展的关键。     

用分子动力学模拟甲烷水合物热激法结合化学试剂法分解

用分子动力学模拟方法研究甲烷水合物的热激法，化学试剂法，以及热激法结合化学试剂法分解，系统研究温度为277K和340K时添加液态水(WTR)和30wt％乙二醇(EG)溶液对水合物分解的影响.模拟显示WTR与水合物表面水分子形成氢键，破坏水合物原有的氢键平衡，造成笼状结构坍塌，水合物分解.EG分子中的羟基与水合物表面水分子形成氢键，从而破坏原有的稳定结构，造成水合物笼状结构被破坏，达到促进水合物分解，释放甲烷气体的效果.比较温度为277K和340K时添加WTR和30wt％EG溶液对水合物分解效果得出EG(340K)> WTR(340K)>EG(277K)>WTR(277K)，热激法结合化学试剂法能更好促进水合物分解.     

水合物储层的毛细封闭效应及高压突破机制

含下伏气的天然气水合物储藏是我国海洋水合物矿藏的重要类型,天然气水合物开采过程中,必须考虑下伏气存在产生的影响。目前,仍缺少针对下伏气产生机理的相关研究。本文利用核磁共振可视化实验装置,探究了水合物藏对其下伏气的封闭作用。结果表明,高饱和度水合物藏对外来流体具有阻碍作用,即毛细封闭作用。水合物的存在减小了孔喉半径,使多孔介质内存在较大的毛细管力,最终形成了抑制下伏气运移的水合物封闭层。水合物储层的封闭效应是下伏气稳定存在的基础。此外,降压过程产生的高压差会诱发水合物封闭层的高压突破现象、进而会引起压力骤降,威胁水合物安全开采。水合物开采过程应该考虑避免出现水合物储层高压突破。     

热学中的新物理量

通过与力学、电学的比拟,在热学中引入了热量的势、势能、速度、动能等新的物理量,从而可建立热量运动的守恒方程组.热量传递是不可逆过程,耗散的是热量的"能量".以耗散最小(热阻最小)为目标函数,就能对传热过程进行优化.傅立叶导热定律是热量运动方程在不计动量变化条件下的简化.在极端(低温、超高速、纳米尺度)条件下不再适用,引入新物理量后,能阐明热波、导热系数尺度效应等"超常"物理现象.     

Numerical Investigation into the Development Performance of Gas Hydrate by Depressurization Based on Heat Transfer and Entropy Generation Analyses

The purpose of this study is to analyze the dynamic properties of gas hydrate development from a large hydrate simulator through numerical simulation. A mathematical model of heat transfer and entropy production of methane hydrate dissociation by depressurization has been established, and the change behaviors of various heat flows and entropy generations have been evaluated. Simulation results show that most of the heat supplied from outside is assimilated by methane hydrate. The energy loss caused by the fluid production is insignificant in comparison to the heat assimilation of the hydrate reservoir. The entropy generation of gas hydrate can be considered as the entropy flow from the ambient environment to the hydrate particles, and it is favorable from the perspective of efficient hydrate exploitation. On the contrary, the undesirable entropy generations of water, gas and quartz sand are induced by the irreversible heat conduction and thermal convection under notable temperature gradient in the deposit. Although lower production pressure will lead to larger entropy production of the whole system, the irreversible energy loss is always extremely limited when compared with the amount of thermal energy utilized by methane hydrate. The production pressure should be set as low as possible for the purpose of enhancing exploitation efficiency, as the entropy production rate is not sensitive to the energy recovery rate under depressurization.     

Numerical Investigation into the Gas Production from Hydrate Deposit under Various Thermal Stimulation Modes in a Multi-Well System in Qilian Mountain

The primary objective of this study was to investigate the energy recovery performance of the permafrost hydrate deposit in the Qilian Mountain at site DK-2 using depressurization combined with thermal injection by the approach of numerical simulation. A novel multi-well system with five horizontal wells was applied for large-scale hydrate mining. The external heat is provided by means of water injection, wellbore heating, or the combinations of them through the central horizontal well, while the fluids are extracted outside from the other four production wells under constant depressurization conditions. The injected water can carry the heat into the hydrate deposit with a faster rate by thermal convection regime, while it also raises the local pressure obviously, which results in a strong prohibition effect on hydrate decomposition in the region close to the central well. The water production rate is always controllable when using the multi-well system. No gas seepage is observed in the reservoir due to the resistance of the undissociated hydrate. Compared with hot water injection, the electric heating combined with normal temperature water flooding basically shows the same promotion effect on gas recovery. Although the hydrate regeneration is more severe in the case of pure electric heating, the external heat can be more efficiently assimilated by gas hydrate, and the efficiency of gas production is best compared with the cases involving water injection. Thus, pure wellbore heating without water injection would be more suitable for hydrate development in deposits characterized by low-permeability conditions.     

Formation and dissociation of gas hydrate inclusions during migration in water

The paper studies the process of floating a gas hydrate particle in liquid. The typical depths when gas bubble floating is accompanied by gas hydrate formation (or with zero gain of hydrate) were calculated. The low depths were identified when floating occurs with hydrate dissociation. The model assumes that the gas hydrate formation is limited by heat transfer from interface to the surrounding liquid. The model for gas hydrate dissociation assumes the rate governed by thermal conductivity of hydrate particle and by convective heat transfer to surrounding water. The temperature of the gas hydrate surface equals the phase transition temperature at the given water pressure. Comparative analysis of thermal conductivity and convective heat transfer effects on hydrate dissociation rate was performed for different initial radius of the particle.     

Study on Hydrate Production Behaviors by Depressurization Combined with Brine Injection in the Excess-Water Hydrate Reservoir

Depressurization combined with brine injection is a potential method for field production of natural gas hydrate, which can significantly improve production efficiency and avoid secondary formation of hydrate. In this work, the experiments of hydrate production using depressurization combined with brine injection from a simulated excess-water hydrate reservoir were performed, and the effects of NaCl concentration on hydrate decomposition, temperature change, and heat transfer in the reservoir were investigated. The experimental results indicate that there is little gas production during depressurization in a excess-water hydrate reservoir, and the gas dissociated from hydrate is trapped in pores of sediments. The high-water production reduces the final gas recovery, which is lower than 70% in the experiments. The increasing NaCl concentration only effectively promotes gas production rate in the early stage. The final cumulative gas production and average gas production rate have little difference in different experiments. The NaCl concentration of the produced water is significantly higher than that which is in contact with hydrate in the sediments because the water produced by hydrate decomposition exists on the surface of undissociated hydrate. The high concentration of NaCl in the produced water from the reactor significantly reduces the promoting effect and efficiency of NaCl solution on hydrate decomposition. The injection of NaCl solution decreases the lowest temperature in sediments during hydrate production, and increases the sensible heat and heat transfer from environment for hydrate decomposition. The changes of temperature and resistance effectively reflect the distribution of the injected NaCl solution in the hydrate reservoir.     

用分子动力学模拟甲烷水合物热激法分解

用分子动力学模拟方法研究甲烷水合物热激法分解，系统地研究注入340 K液态水的结构Ⅰ型甲烷水合物的分解机理.模拟显示水合物表层水分子与高温液态水分子接触获得热能，分子运动激烈，摆脱水分子间的氢键束缚，笼状结构被破坏.甲烷分子获得热能从笼中挣脱，向外体系扩散.热能通过分子碰撞从外层传递给内层水分子，水合物逐层分解.对比注入277K液态水体系模拟结果，得出热激法促进水合物分解. 关键词： 甲烷水合物 分子动力学模拟 热激法     

天然气水化合物的声学探测进展

天然水合物是一种未来的新型能源,与此相关的研究正日益成为能源勘探领域的热点。本文对 天然水合物及其特点、分布和探测技术进行了简要的介绍,在此基础上从声学技术研究角度出发, 介绍了声波测井、地震探测、海底地貌声波检测技术等在探测天然水合物中的应用;并探讨了声学方 法和技术在评价天然水合物储层方面的研究内容、进展和侧重点。     

Clathrate hydrates: recent advances on CH4 and CO2 hydrates,and possible new frontiers

Gas hydrates continue to attract enormous attention throughout the energy industry, as both a hindrance in conventional production and a substantial unconventional resource. Scientists continue to be fascinated by the hydrates’ ability of sequestering large amounts of hydrophobic gases, unusual thermal transport properties and unique molecular structures. Technologically, clathrate hydrates promise advantages in applications as diverse as carbon sequestration and water desalination. The communities interested in hydrates span traditional academic disciplines, including earth science, physical chemistry and petroleum engineering. The studies on this field are equally diverse, including field expeditions to attempt the production of natural gas from hydrate deposits accumulated naturally on the seafloor, to lab-scale studies to exchange CO₂ for CH₄ in hydrates; from theoretical studies to understand the stability of hydrates depending on the guest molecules, to molecular simulations probing nucleation mechanisms. This review highlights a few fundamental questions, with focus on knowledge gaps representing some of the barriers that must be addressed to enable growth in the practical applications of hydrate technology, including natural gas storage, water desalination, CO₂ – CH₄ exchange in hydrate deposits and prevention of hydrate plugs in conventional energy transportation.     

TBAB包络化合物浆水平管内的传热特性研究

TBAB包络化合物浆具有易生成、高潜热及可流动性等特点,是一种良好的蓄冷及潜热输送介质,在中央空调系统中表现出光明的节能前景.本文采用实验方法,研究了B型TBAB包络化合物浆在定热流密度条件下,水平不锈钢管内的对流换热特性,流速涵盖了层流-湍流.通过研究流速V、固相含量X_s对换热系数α的影响,发现"换热降低区"和再层流化现象,得到层流区与湍流区的临界线.最后整理出对流换热的无量纲准则式,其计算结果与实验结果的相对误差在±20%以内.     

Opposed-flow ignition and flame spread over melting polymers with Navier-Stokes gas flow

A numerical model is constructed to predict transient opposed-flow flame spread behaviour in a channel flow over a melting polymer. The transient flame is established by initially applying a high external radiation heat flux to the surface. This is followed by ignition, transition and finally steady opposed-flow flame spread. The physical phenomena under consideration include the following: gas phase: channel flow, thermal expansion and injection flow from the pyrolyzed fuel; condensed phase: heat conduction, melting, and discontinuous thermal properties (heat capacity and thermal conductivity) across the phase boundary; gas-condensed phase interface: radiation loss. There is no in-depth gas radiation absorption in the gas phase. It is necessary to solve the momentum, species, energy and continuity equations in the gas along with the energy equation(s) in the liquid and solid. Agreement is obtained between the numerical spread rate and a flame spread formula. The influence of the gas flow is explored by comparing the Navier-Stokes (NS) and Oseen (OS) models. An energy balance analysis describes the flame-spread mechanism in terms of participating heat transfer mechanisms.     

静止水滴生成气体水合物的动力学研究

作为喷雾强化方式制备气体水合物的初步研究,本文通过研究静止水滴形成气体水合物过程的传热传质机理,建立气体水合物的生成动力学模型。研究结果表明强化气相与水合物颗粒之间的接触传热对提高水合物的生成速率具有十分重要意义。