H31A-01
Variational Scale Separation Methods
We derive a general scale separation method for the continuous variational formulation of the equations for compressible flow in porous media, including source terms and gravity. Restricting the solution to any of the usual mixed finite element spaces will lead to a numerical method exploiting scale separation. We show how particular choices and simplifications reduce the proposed general method to well known methods from literature, such as the variational multiscale method and multiscale mixed finite element method. The work has relevance both in the unification and analysis of existing multiscale methods, as well as in the rigorous development of new multiscale methods.
H31A-02
Small-Scale Modeling of Fluid Displacement Patterns in Layered Porous Media
Naturally occurring porous media are inherently heterogeneous. The depositional characteristics that give rise to permeable formations, and the complex diagenetic processes taking place afterwards, create important heterogeneous features such as bedding planes, fractures, and faults. Rock heterogeneities can have strong impact on fluid displacement patterns because they define preferential flow paths in underground permeable formations. The efficiency of processes of pollution and contaminant removal from soil and groundwater, as well as hydrocarbon recovery, is greatly controlled by our ability to understand and represent fluid transport in heterogeneous permeable media. The present study focuses on a numerical analysis of two-phase flow in fractured rocks exhibiting contrasting rock properties in the form of bedding planes. Simulation scenarios were conducted to monitor contaminant displacement during water imbibition in a synthetic permeable medium model with multiple layers and a single fracture. A commercially available reservoir simulator was used to construct the synthetic three-dimensional model. Previous laboratory observations aid in the construction of the model and interpretation of results. Rock and fluid properties assigned to the synthetic model were estimated from those reported in the literature for a similar rock-fluid system. The presence of bedding planes in the rock's structure was found to have a strong impact on the advancing water front. Temporal saturation maps and fluid displacement patterns are presented in this work for various rates of injection and rock-property contrasts. Even though fracture capillary pressures are often regarded as negligible in the modeling of fractured porous media, our findings suggest that fractures can still provide passages under strong capillary action, which are able to drive wetting fluids into the rock matrix. Such behavior can be captured through proper description of fracture capillary pressures.
H31A-03
Hybrid Numerical Methods for Multiscale Simulations of Biochemical Processes
Many subsurface flow and transport problems of importance today involve coupled non-linear flow, transport, and reaction in media exhibiting complex heterogeneity. In particular, problems involving biological mediation of reactions fall into this class of problems. Recent experimental research has revealed important details about the physical, chemical, and biological mechanisms involved in these processes at a variety of scales ranging from molecular to laboratory scales. However, it has not been practical or possible to translate detailed knowledge at small scales into reliable predictions of field-scale phenomena important for environmental management applications. A large assortment of numerical simulation tools have been developed, each with its own characteristic scale including molecular (e.g., molecular dynamics), microbial (e.g., cellular automata or particle individual-based models), pore (e.g., lattice-Boltzmann, pore network models, and discrete particle methods such as smoothed particle hydrodynamics) and continuum scales (e.g., traditional partial differential equations solved by finite difference or finite element methods). While many problems can be effectively addressed by one or more of these models at a particular scale, some problems as described above will require explicit integration of models across multiple scales. We are developing a hybrid multi-scale subsurface reactive transport modeling framework that integrates models with diverse representations of physics, chemistry and biology at different scales (sub-pore, pore and continuum). The modeling framework is being designed to take advantage of advanced computational technologies including parallel code components using the Common Component Architecture, parallel solvers, gridding, data and workflow management, and visualization. This talk will describe the specific methods/codes being used at each scale, techniques used to directly and adaptively couple across model scales, and preliminary results of application to a multi-scale model of mineral precipitation at a solute mixing interface.
H31A-04
Vorticial Model for Multiphase Flow
Starting from the ideas first presented by Guerlebeck and Sproessig in the sense of describing Navier Stokes equations in terms of quaternionic analysis and find an iterative solution using Teodorescu's integral operator; We modify this concept in order to descibe fluid motions using the expressions of Navier Stokes based on vorticity. We show that Multiphase flow is easily and better described in this way as well as it has an easier numerical expression. We present several examples
H31A-05
Effects of Soil Moisture Dynamics on NAPL Spill Zone Architecture in Two-Dimensional and Three-Dimensional Heterogeneous Porous Media
NAPL distribution in the vadose zone is controlled by the spatial distribution of water saturation and soil permeability, the NAPL spill scenario, water infiltration events, and vapor transport. The effects of these processes in two-dimensional and three-dimensional heterogeneous porous media were investigated using the three-phase flow simulator, Subsurface Transport Over Multiphase Phases (STOMP). A 3-D heterogeneous field with five stratigraphic layers was assumed and a 2-D vertical cross-section along the center of the 3-D field was used for the 2-D simulations. The conceptual model of the soil heterogeneity was based upon the stratigraphy at the Hanford carbon tetrachloride (CT) spill site. Co-disposal of NAPL with large volumes of wastewater was considered, as also occurred at the Hanford CT site. The same NAPL and water infiltration rates were used in 2- D and 3-D simulations. The form and location of NAPL were most strongly influenced by spill area (i.e., CT infiltration rate), high water discharge rates and NAPL evaporation to the atmosphere. The front of NAPL reached the groundwater table faster in 3-D than in 2-D. However, the fraction of total CT mass that reached the groundwater table was higher in 2-D than in 3-D. The difference between 2-D and 3-D simulations can be primarily attributed to the following factors. First, water saturation in the low permeability layer was lower in 3-D than in 2-D because the water plume spread out more evenly due to the additional horizontal direction in the 3D case. Hence, the NAPL front can penetrate through the low permeability layer due to the increased NAPL relative permeability and less capillary barrier effect in the low permeability layer, while in the 2-D case the water saturation in the low permeability layer was close to one during vertical migration of the wastewater plume. Second, the effect of density-driven vapor transport in 3-D was more significant than in 2-D, mainly due to the presence of the additional horizontal direction for vapor transport in 3-D. Hence, more CT mass moved out of the NAPL source zone in the 3-D simulation, resulting in a lower fraction of the total NAPL mass in groundwater. These simulations indicate that the 2-D simulation for organic compounds with high vapor pressure need to be compared with the 3-D simulation, in particular, under simultaneous water infiltration scenarios. The effect of variability in the permeability field and quantitative analysis of dimensionality on NAPL distribution will be further exploited through stochastic modeling.
H31A-06
Nonaqueous Phase Liquid Dissolution Characteristics and Large-Scale Subsurface Contaminant Transport Modeling
Subsurface contamination by organic chemicals in the form of nonaqueous phase liquids (NAPLs) is a widespread problem which poses a serious threat to groundwater resources. Over the last decade some significant advances have been made in determining NAPL-aqueous phase mass transfer (dissolution) characteristics. However, most of these studies have been conducted in relatively simple and homogeneous one-dimensional columns at relatively small laboratory scales. In this study, we try to determine the differences of large-scale transport characteristics using existing mass transfer rate correlations which showed very similar predictions over mass transfer rate at laboratory scales. Some of the recently developed dissolution rate coefficient correlation formulations are used to simulate the rate-limited dissolution processes. One-dimensional aqueous phase simulations are performed to examine differences among these correlations by comparing effluent concentrations. Damkohler number analysis is used to determine degree of equilibrium for each correlation and extent of error introduced by assuming local equilibrium between the NAPL and aqueous phases. Numerical models are also used to simulate two-dimensional two-phase flow and NAPL fate and transport. The simulation results illustrate the significance of the system scale on the rate of mass transfer between phases and the degree of equilibrium.