不同水合物饱和度下注热水开采实验研究

为研究不同水合物藏饱和度对注热开采动态的影响,采用自制的一维天然气水合物(NGH)开采模拟实验装置,模拟地层多孔介质的条件,首先在填砂模型中生成不同饱和度的NGH,然后进行注热盐水分解实验。结果表明:不同饱和度的NGH注热分解产气都可划分为三个阶段,不同的是NGH饱和度越高,水合物分解阶段的产气速率越大,且该阶段持续的时间越长;NGH饱和度越高,注热分解阶段电阻率增大的幅度越大,系统各测点温度升高的幅度越小。注热分解过程中产水速率围绕注水速率而上下波动,且NGH饱和度越高,产水速率波动幅度越大;在实验研究范围内,随初始水合物饱和度的升高,注热开采的能量效率逐渐升高。因此,从能量效率来说,高饱和度的水合物藏更适宜于注热开采。     

多孔介质中天然气水合物注热+降压开采的实验研究

为研究注热与降压相结合的开采方式是否更加有利于天然气水合物的开采,在自制的天然气水合物开采模拟实验系统上进行了实验研究.在一维填砂模型中人工生成天然气水合物之后,进行先注热盐水然后再降低压力(注热+降压)的开采模拟实验,分析了开采过程中系统温度、电阻率变化规律以及产气量、能量效率等.结果表明:产气规律具有明显的阶段性,...     

一种新型螺旋内槽管的气液固三相流数值模拟研究

针对一种新型螺旋内槽管,采用先进的计算流体力学(CFD)数值模拟方法,对管内的气(天然气)-液(水)-固(水合物)三相流流动特性进行了模拟研究。模型采用欧拉-欧拉-欧拉三流体模型结合颗粒动力学的理论,考察了不同的表观速度(0.3 m/s,0.5 m/s,0.7 m/s),水合物粒径(500μm,750μm,1000μm),气泡大小(10μm,100μm,1000μm),螺距(400mm,800mm),螺纹头数(12,20)及螺纹旋向对于管内三相流动特性的影响。通过数值计算,由于气液固三相间的密度差,在螺旋内槽的作用下,水合物和天然气在管中心位置聚集,同时管壁处的含量减小。流体表观流速和气泡越大,壁面处的水合物和天然气的体积分数越小;由于天然气的密度小于水合物和水的密度,天然气更多集中在管中心,越靠近管壁含量越少;颗粒的粒径越大,壁面处的水合物含量越少,而对于天然气的分布则影响不大;螺距越小,螺纹头数越多,螺旋流强度越大,气液固三相分离效果越好,壁面处的水合物和天然气的含量越小;同时,螺纹旋向的改变对于三相的分离效果影响较小。     

一种新型螺旋内槽管的气液固三相流数值模拟研究

针对一种新型螺旋内槽管,采用先进的计算流体力学（CFD）数值模拟方法,对管内的气（天然气）-液（水）-固（水合物）三相流流动特性进行了模拟研究。模型采用欧拉-欧拉-欧拉三流体模型结合颗粒动力学的理论,考察了不同的表观速度（0.3 m/s,0.5 m/s,0.7 m/s）,水合物粒径（500 μm,750 μm,1000 μm）,气泡大小（10 μm,100 μm,1000 μm）,螺距（400 mm,800 mm）,螺纹头数（12,20）及螺纹旋向对于管内三相流动特性的影响。通过数值计算,由于气液固三相间的密度差,在螺旋内槽的作用下,水合物和天然气在管中心位置聚集,同时管壁处的含量减小。流体表观流速和气泡越大,壁面处的水合物和天然气的体积分数越小;由于天然气的密度小于水合物和水的密度,天然气更多集中在管中心,越靠近管壁含量越少;颗粒的粒径越大,壁面处的水合物含量越少,而对于天然气的分布则影响不大;螺距越小,螺纹头数越多,螺旋流强度越大,气液固三相分离效果越好,壁面处的水合物和天然气的含量越小;同时,螺纹旋向的改变对于三相的分离效果影响较小。     

深水井控过程中天然气水合物生成区域预测

针对深水井控的特点,建立了多相流控制方程,给出了温度场方程和水合物生成热力学方程,并给出了不同工况下求解上述方程的定解条件和离散方法以及求解步骤.数值计算表明:随着关井时间的增加,环空内的温度越接近环境温度,水合物的生成区域越大;随着压井排量的增加,天然气水合物的生成区域变小,可适当提高流量使水合物的生成区尽量远离海底,减小防喷器管线被水合物阻塞的危险;由于节流管线摩阻的原因,与钻进时相比,压井时水合物的生成区域会变大,且随着节流管线内径的减小,水合物的生成区域会变大;随着抑制荆浓度的提高或钻井液入口温度的升高,天然气水合物的生成区域也随之变小.     

天然气水合物降压开采沉积物压缩效应数值模拟研究

深海天然气水合物降压开采过程中,沉积物的压缩会改变储层的物理力学特性,进而对天然气的开采效果产生显著影响.为揭示沉积物压缩效应下井周围储层物理力学特性演化规律,本文建立了考虑沉积物压缩效应的理论模型,通过COMSOL模拟研究了不同初始固有渗透率、初始水合物饱和度和井底压力条件下的降压开采中生产井周围储层的物理力学特性演化规律以及开采效果.结果表明:受沉积物压缩的影响,水合物分解区的渗透率随着与井筒距离的增加先增加后减少;产气与产水速率由零立即上升至峰值,然后迅速下降,并且考虑沉积物压缩时的产气与产水速率比不考虑时低;在水合物完全分解区,渗透率的大小与有效应力成负相关关系,未分解区渗透率的大小与水合物饱和度成负相关关系;井底压力越小,有效应力越大,生产井周围储层的渗透率下降越明显;初始水合物饱和度对产气与产水的影响存在拐点,饱和度拐点位于0.25与0.35之间,高水合物饱和度并不代表储层开采效果好,产气速率的高低还与储层的渗透率有关,高水合物饱和度储层的渗透率较低,产气速率较低;储层初始固有渗透率较高时显著促进了开采效果,但储层变形量较大增加了储层的不稳定性.     

天然气水合物开发多物理场特征及耦合渗流研究进展与建议

天然气水合物作为一种非常规的清洁能源,在全球分布广、资源量大.自20世纪90年代以来,加拿大、美国、日本、中国已经先后进行了陆域及海域的水合物试采,但发现出砂、单井日产气量低、稳产时间短等问题,试采产量远不能满足商业化开发的需求,其中核心问题是对水合物开发过程中的相变、多相多组分多场耦合渗流特征的认识不够明晰.本文根据天然气水合物开发过程中涉及的渗流场、温度场、化学场、力学场等多场耦合特征,重点综述水合物生成/分解对各物理场主要特征参数的影响,包括水合物储层的孔隙度、水合物饱和度、渗透率、相对渗透率等基础物性参数及其动态演变,天然气水合物的导热系数、比热容、热扩散系数以及水合物生成/分解热等热力学参数,天然气水合物生成、分解动力学特征,纯水合物以及含水合物沉积物的力学性质等,最后阐述了天然气水合物开发渗流中的多场耦合关系及相互作用,提出了今后水合物开发多物理场特征及耦合渗流的科学研究、技术开发的有关建议.     

天然气水合物开发多物理场特征及耦合渗流研究进展与建议

天然气水合物作为一种非常规的清洁能源, 在全球分布广、资源量大. 自20世纪90年代以来, 加拿大、美国、日本、中国已经先后进行了陆域及海域的水合物试采, 但发现出砂、单井日产气量低、稳产时间短等问题, 试采产量远不能满足商业化开发的需求, 其中核心问题是对水合物开发过程中的相变、多相多组分多场耦合渗流特征的认识不够明晰. 本文根据天然气水合物开发过程中涉及的渗流场、温度场、化学场、力学场等多场耦合特征, 重点综述水合物生成/分解对各物理场主要特征参数的影响, 包括水合物储层的孔隙度、水合物饱和度、渗透率、相对渗透率等基础物性参数及其动态演变, 天然气水合物的导热系数、比热容、热扩散系数以及水合物生成/分解热等热力学参数, 天然气水合物生成、分解动力学特征, 纯水合物以及含水合物沉积物的力学性质等, 最后阐述了天然气水合物开发渗流中的多场耦合关系及相互作用, 提出了今后水合物开发多物理场特征及耦合渗流的科学研究、技术开发的有关建议.      

有效应力升降过程中不同饱和度水合物沉积物渗透率实验研究

为了研究天然气水合物开采过程中水合物饱和度和有效应力变化对含水合物沉积层渗透率变化规律的影响,利用自主研制的水合物沉积物合成与三轴渗流实验一体化装置,进行了有效应力升降过程中不同饱和度水合物沉积物渗透性实验。结果表明:有效应力升降过程中,不同饱和度水合物沉积物的渗透率与有效应力均呈负指数规律变化,并表现出在低有效应力阶段渗透率变化的幅度大于高有效应力阶段;有效应力升降过程中,试样产生的不可恢复变形使渗透率不能完全恢复,造成渗透率永久损失;有效应力不变时,水合物沉积物的渗透率与水合物饱和度呈负指数规律变化,且曲线的斜率随饱和度增加由大变小;水合物的饱和度越大,最大渗透率损害率越大,渗透率恢复的程度越差。     

页岩气吸附解吸规律研究

页岩中天然气的吸附解吸规律是页岩气开发的基础。根据物质平衡原理,自行设计了页岩气吸附解吸实验装置。用该装置对取自鄂尔多斯盆地的三个页岩岩样在不同温度(30～90℃)、不同压力(0.1～10MPa)条件下,进行页岩气吸附及解吸规律研究。实验结果表明,吸附量随有机碳含量的增加而增大;随压力的增加吸附量增大,而随温度的增大吸附量减小。同一温度压力条件下,相对吸附过程而言,解吸过程有滞后现象,解吸不够彻底。对粘土含量较大的页岩,朗格缪尔模型拟合效果较差,而利用修正的双朗格缪尔模型可以得到较好的拟合结果。     

电阻率测试技术在沉积物-盐水-甲烷水合物体系中的应用

利用自制的一维天然气水合物(NGH)开采模拟实验系统,通过对NGH生成过程中电阻率、温度、压力等的变化规律进行分析,验证了在海洋沉积物体系中用电阻率法测试NGH的可行性。实验结果表明,电阻率可以清楚地反映NGH的成核及生长过程。NGH开始成核时消耗了溶液中的水分和甲烷气体,增加了离子之间的连通性,使电阻率降低;晶核开始生长为NGH后,由于生成的NGH类似于绝缘体,并且使得孔隙连通性变差,电阻率逐步升高,NGH大量生成后电阻率保持稳定。然后进行NGH降压分解实验,随着NGH的分解,NGH饱和度下降,电阻率也逐渐下降。     

Modeling of Gas Hydrate Formation Upon Injection of Carbon Dioxide Gas into A Natural Reservoir

This paper presents the results of numerical modeling of gas hydrate formation upon injection of carbon dioxide into a finite-length reservoir saturated with methane and water. It is shown that at different stages, hydrate formation can occur on both the frontal surface and in a reservoir region of finite length. The effects of pressure at the reservoir boundaries and the effects of the permeability and initial water saturation of the reservoir on the hydrate formation process were studied. The dependences of the time of the complete conversion of water into gas hydrate in the entire reservoir on the injection pressure and reservoir permeability were obtained.     

After fogging process in water injected gas turbine systems

In gas turbine system with after fogging, water droplets are injected after compressor. After fogging could have more significant potential for enhancement of specific power production compared to inlet fogging alone, since a larger water injection rate is possible. Transient analysis of after fogging process is carried out by using a heat and mass transfer modeling on water droplet evaporation. Transient variables such as droplet diameter and air temperature are evaluated as the droplet evaporation proceeds for different values of initial droplet diameter, pressure ratio of compressor, and water injection ratio. The evaporation time for injected droplets are also estimated. Present results show that the evaporation time decreases sensitively with increasing pressure ratio or initial droplet diameter. However, the effect of water injection ratio on evaporation time is relatively insignificant unless water injection ratio is near the critical ratio.     

Injection of A Hydrate-Forming Gas into A Snow Layer Saturated with the Same Gas

The problem of injection of a hydrate-forming gas (methane) into a snow layer whose pores are initially saturated with the same gas is solved. Self-similar solutions describing the temperature and pressure fields and the snow, hydrate, and gas distributions in the layer are constructed. It is shown that, depending on the initial thermobaric state of the snow–methane system and the rate of gas injection, three characteristic zones can be distinguished in the filtration region: a near zone, in which snow is completely converted into hydrate and, consequently, the hydrate layer is saturated with gas; an intermediate zone, in which gas, snow, and hydrate are in phase equilibrium; far zone filled with gas and snow. It is shown that the length of the heated zone decreases with increasing initial snow content in the layer and with decreasing injected gas pressure. It is also shown that the length of the region of hydrate formation increases with increasing permeability. It is noted that the heating of the intermediate zone occurs more rapidly.     

油田注水开发中水嘴节流与地层渗流耦合研究

配水器的选取会对油田注水效果产生明显影响。为精确地描述注水井注入过程中井底压力和流量的动态响应,本文在传统的内边界井处理模型的基础上建立了考虑水嘴压力损失影响的井处理模型。耦合求解井底压力、流量及地层流动,得到了注入过程中考虑水嘴压力损失影响的井底压力和流量响应情况。以此来分析不同水嘴、渗透率对井底压力、注入量随时间变...     

In-Situ Capillary Trapping of CO<Subscript>2</Subscript> by Co-Injection

Co-injection of water with CO₂ is an effective scheme to control initial gas saturation in porous media. A fractional flow rate of water of approximately 5–10% is sufficient to reduce initial gas saturations. After water injection following the co-injection, most of the gas injected in the porous media is trapped by capillarity with a low fractional volume of migrating gas. In this study, we first derive an analytical model to predict the gas saturation levels for co-injection with water. The initial gas saturation is controlled by the fractional flow ratio in the co-injection process. Next, we experimentally investigate the effect of initial gas saturation on residual gas saturation at capillary trapping by co-injecting gas and water followed by pure water injection, using a water and nitrogen system at room temperature. Depending on relative permeability, initial gas saturation is reduced by co-injection of water. If the initial saturation in the Berea sandstone core is controlled at 20–40%, most of the gas is trapped by capillarity, and less than 20% of the gas with respect to the injected gas volume is migrated by water injection. In the packed bed of Toyoura standard sand, the initial gas saturation is approximately 20% for a wide range of gas with a fractional flow rate from 0.50 to 0.95. The residual gas saturation for these conditions is approximately 15%. Less than approximately 25% of the gas migrates by water injection. The amount of water required for co-injection systems is estimated on the basis of the analytical model and experimental results.     

Investigating the Fracture Network Effects on Sweep Efficiency during WAG Injection Process

In this study, the main recovery mechanisms behind oil/water/gas interactions during the water-alternating-gas (WAG) injection process, in a network of matrix/fracture, were fundamentally investigated. A visual micromodel was utilized to provide insights into the potential applications of WAG process in fractured oil-wet media as well as the possibility of observing microscopic displacement behavior of fluids in the model. The model was made of an oil-wet facture/matrix network system, comprised of four matrix blocks surrounded with fractures. Different WAG injection scenarios, such as slug arrangements and the effects of fluid injection rates on oil recovery were studied. A new equation representing the capillary number, considering the fracture viscous force and matrix capillary force, was developed to make the experimental results more similar to a real field. In general, WAG tests performed in the fractured model showed a higher oil recovery factor compared with the results of gas and water injection tests at their optimum rates. The results showed that the presence of an oil film, in all cases, was the main reason for co-current drainage and double displacement of oil under applied driving forces. Furthermore, the formation of oil liquid bridges improved the recovery efficiency, which was greatly influenced by the size of fracture connecting the two matrix blocks; these connecting paths were more stable when there was initial water remaining in the media. Analyzing different recovery curves and microscopic view of the three phases in the transparent model showed that starting an injection mode with gas (followed by repeated small slugs of water and gas), could considerably improve oil recovery by pushing water into the matrix zone and increasing the total sweep efficiency.     

瓦斯/空气预混气体爆燃流场测试系统多参数耦合同步控制实验方法

为了更精确地获得爆炸激波管内瓦斯/空气预混气体爆燃过程中，激波形成过程、压力和火焰传播速度以及火焰与惰性阻燃剂相互作用的流场演化图像。通过分析激波管测试系统中多个目标的时间响应特征及控制方式，利用超高速相机、光电倍增管、时间延时器、固态继电器、电荷放大器和数据采集系统等设备，设计实验方案，分别对激波管中瓦斯/空气预混气体爆燃高压点火系统的响应时间和惰性介质阻燃剂喷射系统的响应时间进行测试。实验结果表明电火花点火的响应时间为微秒量级，而阻燃剂喷射系统的响应时间为毫秒量级，以响应时间为依据，通过设置精确的延迟时间实现多目标同步控制，为完成激波管内瓦斯/空气预混气体爆燃过程的微观流场显示奠定基础。