【作者】 刘瑜；

【导师】 宋永臣；

【作者基本信息】 大连理工大学 ， 能源与环境工程， 2011， 博士

【摘要】 温室气体二氧化碳的大量排放给全球气候和环境带来的巨大影响已经引起了全世界的广泛关注。实现二氧化碳的深度减排是人类可持续发展的必由之路。人为的将二氧化碳封存到地层中和利用二氧化碳驱油提高采收率是实现二氧化碳深度减排的两个可选途径。在成熟的技术方案和合理的封存场地得到保证的前提下,二氧化碳地下封存是封存储量最大、前景最好的二氧化碳减排方案。而利用二氧化碳驱油提高采收率不但可以封存二氧化碳还能够提高石油可采储量,是一种实现社会效益和经济效益双赢的二氧化碳减排方案。本文以开发二氧化碳长期、安全封存技术为研究背景,在实验室内模拟二氧化碳封存的沉积层环境,研究海底沉积层中二氧化碳水合物封存、二氧化碳咸水层封存和二氧化碳驱油提高采收率过程中的基础问题,获得相关的实验数据和规律,为阐明二氧化碳封存中的相关机理提供支持。首先开发了一套模拟海洋沉积层环境的填砂水合物相平衡实验系统,系统具有较高的测量精度和易操作性。该系统可以通过填砂方式模拟海洋沉积层,通过改变填砂粒径尺寸来改变沉积层的孔隙尺寸,还可以模拟含盐分的海水进行相关实验研究。应用填砂水合物相平衡实验系统开展了多孔介质的孔隙尺寸、孔隙水盐度和二氧化碳混合氮气对二氧化碳水合物相平衡的影响特性研究。通过研究发现随着孔隙尺寸减小、孔隙水盐度增大和混入氮气百分比的增加,二氧化碳水合物相平衡向高压、低温方向移动。与在纯水中相比在海洋沉积层中二氧化碳水合物需要更高的压力和更低的温度保持其稳定性。通过对水合物生成过程中多孔介质渗透率的测量,发现渗透率随水合物饱和度成指数下降趋势。基于磁共振成像仪(MRI)开发了沉积层中二氧化碳水合物可视化实验系统和二氧化碳-水-油多相流动的可视化实验系统。系统以一台400MHz磁共振成像仪为主体,周边设备采用通用设备组合的方式来满足多种实验需求。应用MRI对多孔介质中水合物生成过程的诱导时间、饱和度等参数以及水合物生长模式进行了定量测量和可视化分析。实验结果表明水合物生成诱导时间随过冷度增大和压力升高而大大降低,而水合物生成的饱和度和过冷度、压力成正比关系。通过对水合物生长模式的研究发现在玻璃砂堆积多孔介质中水合物主要以胶结模式生成。对填砂多孔介质的孔隙度进行了MRI平均亮度法分析,与传统的孔隙度测量方法获得的孔隙度吻合较好,并且得到了多孔介质的局部孔隙度。在进行模拟沉积层中超临界二氧化碳驱水实验研究时发现,由于浮升力的作用二氧化碳在含孔隙水多孔介质中有明显的窜流和指进现象,特别是某些局部渗透率较大的通道是二氧化碳在咸水层封存中产生流动“惰性”的主要因素。通过MRI相位迁移速度成像法可以准确测量多孔介质中水的流速分布,通过MRI饱和度分析和达西渗透理论结合能够获得二氧化碳在多孔介质中的流速分布。采用MRI图像亮度分析可以准确判断二氧化碳与油的混相状态,并且通过对压力与图像亮度的拟合可以定量获得最小混相压力。在简单通道内水驱油的实验结果表明,润湿特性对水驱效果有较大影响,在并联孔隙中容易产生孤立油珠,被圈闭在孔隙中的油珠是残余油形成的一个主要因素。对二氧化碳非混相气驱与超临界二氧化碳混相驱进行了对比研究,发现超临界二氧化碳混相驱形成活塞状的驱替前缘可以提高扫掠效率、延长突破时间,是混相驱效率优于非混相驱的一个重要原因。二氧化碳混相驱最终的驱替效率要远远高于非混相驱。更多还原

【Abstract】 It has been widely concerned about the impacts on global climate and environment caused by carbon dioxide (CO2) green-house gas emission. Mitigation of CO2 emission to the atmospere has great importance to the sustainable development of mankind. CO2 underground sequestration and enhanced oil recovery are the two main options of many mitigation metods. Underground sequestration based on mature techniques and appropriate locations is a method with the most potential capacity. On the other hand, enhanced oil recovery is considered to be a win-win method for both economic and environmental benefits because it may not only storage CO2 underground but also improve oil recoverable reserves. This project is proposed against the background of long term and safe storage of CO2. Experiments for CO2 storage in artificial sediments were inducted at laboratory scale. Fundamental studies on CO2 hydrate storage in ocean sediments, storage in saline aquifer and enhanced oil recovery were carried out for obtaining basic data and mechanism in expectation of theoretical support for CO2 sequestration.A high precision and maneuverable experimental system for CO2 hydrate equilibrium study in simulated ocean sediments was developed. Ocean sediment environment with different pore size and salinity was built up using glass beads with different grain size and brine with different concentration.Experimental studies on the effect of pore size, salinity and nitrogen fraction on CO2 hydrate equilibrium were carried out using the experimental system of hydrate equilibrium. Results showed that equilibrium of CO2 hydrate moves toward high pressure and low temperature direction as pore size decreses as well as salinity and nitrogen faction increases. It needs higer pressure and lower temperature for the stability of CO2 hydrate in ocean sediments than in pure water. It was also shown that permeability decreases exponentially with hydrate saturation as hydrate grows in porous media.Another experimental system based on a 400 MHz magnetic resonance imaging (MRI) device and its peripheral equipments was also developed which can be applied to the visualization of CO2 hydrate and CO2-water-oil multiphase flow in porsous media.Induction time and saturation were measured and growth pattern was visualized as hydrate formed in porous media. Results showed that induction time decreases greatly as super cooling temperature and initial pressure increase. Final saturation of hydrate was linear relation with super cooling temperature and initial pressure. Hydrate grows in a pattern of cementing with glass beads pack-simulated sediments in our experiments.Porosity obtained using MRI intensity analysis was shown to be identical with tradition methods and local porosity was also obtained. Channeling and fingering phenomenon arose by buoyancy was obviously detected in CO2 flooding through water saturated sediments. Experiment results showed that paths with higher permeability are the main reasons which make CO2 become lazy in saline aquifer storage. Phase velocities of water and CO2 flowing in porous media were also obtained by using MRI pahse shift imaging and MRI saturation analysis combined with Darcy’s theory.Miscible status of CO2 with oil was detected and minimum miscibility pressure (MMP) was quantified exactly using MRI intensity analysis. Water flooding experiments in simple channels showed that wettability has great effect on oil displacement. Results showed that isolated oil drops trend to form in bifurcate channels which is a main inducement of oil trap after water flooding.Comparison of immiscible and miscible displacement of CO2 showed that pistion-like miscible zone of CO2 and oil can improve the sweep coefficiency and enlarge the breakthrough time during CO2 flooding. It showed that a much higher displacement coefficient can be obtained in CO2 miscbile displacement than in immiscible displacement.更多还原