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

9817823 Welty 1997-98年休假期间，PI在德国的卡塞尔大学工作，建造了一个大型实验容器，其中包含结构化、相关、随机多孔介质，可用于在受控实验室条件下观察任何流体流动或感兴趣的质量输运问题。 这项工作是与内内斯科罗拉多学校的蒂萨伊兰加塞卡雷博士合作进行的，伊兰加塞卡雷博士在建造这种容器和进行大规模实验室实验研究方面有近20年的经验。 卡塞尔大学地质水力学和工程水文学系主任Manfred Koch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。本提案中所述研究的主要目标是在新设备上进行第一组实验，一系列的运行，以量化渗透率的非均质性和高溶质浓度之间的相互作用，这种相互作用对饱和多孔介质中的宏观分散的影响。 为此，将对1997- 1998年期间研制的仪器进行测试，并将继续加以改进，作为在卡塞尔大学研制一种专门的多孔介质观测设施的进一步步骤，供来自世界各地的研究人员使用。 虽然众所周知，溶质羽流的密度可以影响其平均运动，流体密度对流体混合或有效分散在非均质多孔介质中的流体的影响还没有系统地记录从观测的角度来看。 定性的实验证据和理论预测表明，密度梯度与非均匀性程度的相互作用影响分散：渗透率的非均匀性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/溶剂的流动配置。 对比密度的流体（实验室级水和NaCl溶液）将在（1）阶跃输入水平位移和（2）密度分层的水平流动配置中通过建造的储罐进行位移。 水平位移将在稳定和不稳定流配置下运行;分层流配置将在稳定配置下运行。 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。 溶质浓度的测量，使用溶液采样器在时间和空间上将进行比较，预测的宏观分散的致密，混溶流体的基础上现有的随机理论先前开发的PI。 研究结果既可以证实前人的理论工作，也可以为这一领域的进一步理论发展提供动力。 这种方法，加上正在进行的数值模拟，将有助于统一理解这一耦合过程所需的知识，以帮助预测含水层中稠密、可混溶流体的大规模迁移。 这个知识库，然后可以作为基础，用于评估额外的，现实的非理想的过程通常与密度耦合混相传输，如热过程和非均相地球化学reactions.The工作的分散效果建议进行在大学的卡塞尔由于异常慷慨的资源基础，将继续提供那里的学生和实验室技术人员的支持。（科罗拉多矿业学校的类似设施在感兴趣的时期内无法用于开展拟议的工作。）本提案中的预算用于支付主要研究员的工资和相关费用，以便继续在卡塞尔大学开展为期两年的合作，进一步开发多孔介质观测设施，并在该设施中开展第一批实验。

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.