Density-Coupled Transport in Heterogeneous Porous Media: Ob servations and Comparison to Stochastic Theory

9817823 wely在1997-98年的公休假期间，PI在德国卡塞尔大学工作，建造了一个大型实验容器，其中包含结构化的，相关的，随机的多孔介质，可用于在受控实验室条件下观察任何流体流动或质量传输问题。这项工作是与内内斯科罗拉多学院的Tissa Illangasekare博士合作进行的，他在建造这种船只和进行大规模实验室实验研究方面有近20年的经验。卡塞尔大学岩土水力学与工程水文学系主任曼弗雷德·科赫博士为这项工作提供了设备、用品、实验室技术人员时间和学生支持。本提案中所述的研究的主要目的是在新设备上进行一系列实验，以量化渗透率非均质性与高溶质浓度之间的相互作用，以及这种相互作用对饱和多孔介质中宏观分散的影响。在此过程中，将对1997- 1998年研制的仪器进行测试，并将继续进行改进，作为在卡塞尔大学研制专门的多孔介质观测设备的进一步步骤，供世界各地的研究人员使用。提出的实验集将检验假设，即密度相关输运中的宏观色散可以通过现有的随机理论来预测。尽管众所周知，溶质羽流的密度会影响其平均运动，但从观测的角度来看，流体密度对具有统计特征的非均质多孔介质中流体混合或有效分散的影响尚未得到系统的记录。定性实验证据和理论预测表明，密度梯度与非均质程度的相互作用影响分散性：渗透率非均质可以减弱或增强密度梯度对溶质扩散的影响，这取决于溶质/溶剂的流动结构。实验将在实验室进行，以确保等温条件，并避免不必要的地球化学反应。不同密度的流体（实验室级水和NaCl溶液）将以(1)阶梯输入的水平位移和(2)密度分层的水平流动配置方式通过构建的储罐进行置换。水平驱替将在稳定和不稳定两种流态下进行；将运行分层流配置以获得稳定配置。每种流体驱替方案将在两种平均孔隙速度和三种盐浓度下运行。使用溶液采样器测量的溶质浓度随时间和空间的变化将与PI先前开发的基于现有随机理论的致密混相流体的宏观分散预测进行比较。这些结果将有助于证实以前的理论工作，或将为该领域的进一步理论发展提供动力。这种方法与正在进行的数值模拟相结合，将有助于获得对这一耦合过程的统一理解所需的知识，以帮助预测含水层中致密、可混溶流体的大规模输送。然后，这个知识库可以作为评估通常与密度耦合混相输运相关的额外的、现实的非理想过程（如非均匀过程和非均相地球化学反应）对分散的影响的基础。这项工作被提议在卡塞尔大学进行，因为那里的资源基础非常丰富，将继续为学生和实验室技术人员提供支持。（科罗拉多矿业学院的类似设施将无法在相关期间进行拟议的工作。）本提案中的预算用于支付PI的工资和相关费用，以继续她在卡塞尔大学的两年合作工作，进一步开发多孔介质观测设施，并在该设施中进行第一批实验。

9817823WeltyDuring her 1997-98 sabbatical leave, the PI has worked at University of Kassel in Germany to build a large-scale experimental vessel containing structured, correlated, random porous media that can be used for observations of any fluid flow or mass transport problem of interest under controlled laboratory conditions. This effort has been carried out in collaboration with Dr. Tissa Illangasekare of the Colorado School of NEnes, who has nearly twenty years of experience in building such vessels and in carrying out large-scale laboratory experimental research. Dr. Manfred Koch, Director of the Department of Geohydraulics and Engineering Hydrology at University of Kassel, has provided equipment, supplies, lab technician time, and student support for the work.The principal objective of the research described in this proposal is to carry out, as a first set of experiments in the new apparatus, a series of runs to quantify the interaction between permeability heterogeneity and high solute concentrations and the effect of this interaction on macrodispersion in saturated porous media. In doing so, the apparatus developed during 1997-98 will be tested and will continue to undergo refinement, as a further step in developing a dedicated porous media observational facility available to researchers from around the world at the University of Kassel.The set of proposed experiments will test the hypothesis that macrodispersion in densitydependent transport can be predicted by existing stochastic theory. Although it is well known that the density of a solute plume can affect its mean motion, the effect of fluid density on fluid mixing or effective dispersion in statistically-characterized heterogeneous porous media has not been systematically documented from an observational standpoint. Qualitative experimental evidence and theoretical predictions indicate that interaction of the density gradients with degree of heterogeneity affects dispersion: the permeability heterogeneity can damp out or enhance the effects of the density gradients on solute spreading depending on the solute/solvent flow configuration.The experiment is to be conducted in the laboratory to ensure isothermal conditions and to avoid unwanted geochemical reactions. Fluids of contrasting density (laboratory-grade water and NaCl solutions) will be displaced through the constructed tank in (1) a step-input horizontal displacement, and (2) a density-stratified, horizontal flow configuration. The horizontal displacements will be run for both stable and unstable flow configurations; the stratified flow configuration will be run for a stable configuration. Each fluid displacement scenario will be run for two mean pore velocities and three salt concentrations. Measurements of solute concentration made using solution samplers over time and space will be compared to predictions of macrodispersion of dense, miscible fluids based on existing stochastic theory previously developed by the PI. The results will either serve to confirm previous theoretical work, or will provide impetus for further theory development in this area. Such an approach, together with ongoing numerical simulations, will contribute to knowledge needed for a unified understanding of this coupled process to aid in predicting large-scale transport of dense, miscible fluids in aquifers. This knowledge base can then serve as the foundation for evaluating the effect on dispersion of additional, realistic non-ideal processes typically associated with density-coupled miscible transport, such as then-nal processes and heterogeneous geochemical reactions.The work is proposed to be carried out at University of Kassel due to the unusually generous resource base that will continue to be available there for student and lab technician support. (Similar facilities at the Colorado School of Mines would not be available during the period of interest to carry out proposed work.) The budget in this proposal is to cover salary and related expenses of the PI to continue her collaborative effort at University of Kassel for an additional two years to further develop the porous media observational facility and to carry out a first set of experiments in this facility.