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A MOUNTAIN-SCALE 3-D NUMERICAL MODEL FOR CHARACTERIZING UNSATURATED FLOW AND TRANSPORT IN FRACTURED VOLCANIC ROCK AT YUCCA MOUNTAIN

Description: A three-dimensional site-scale numerical model has been developed to simulate water and gas flow, heat transfer, and radionuclide transport in the unsaturated zone of Yucca Mountain, Nevada, the American underground repository site for high level radioactive waste. The modeling approach is based on a mathematical formulation of coupled multiphase fluid and heat flow and tracer transport through porous and fractured rock. This model is intended for use in predicting current and future conditions in the unsaturated zone, so as to aid in assessing the system performance of the repository. In particular, an integrated modeling methodology is discussed for integrating a wide variety of moisture, pneumatic, thermal, and isotopic geochemical data into comprehensive modeling analyses. The reliability and accuracy of the model predictions were the subject of a comprehensive model calibration study, in which the model was calibrated against measured data, including liquid saturation, water potential, and temperature. This study indicates that the model is able to reproduce the overall system behavior at Yucca Mountain with respect to moisture profiles, pneumatic pressure and chloride concentration variations in different geological units, and ambient geothermal conditions.
Date: February 28, 2006
Creator: Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

Analysis of stress sensitivity and its influence on oil productionfrom tight reservoirs

Description: This paper presents a study of the relationship betweenpermeability and effective stress in tight petroleum reservoirformations. Specifically, a quantitative method is developed to describethe correlation between permeability and effective stress, a method basedon the original in situ reservoir effective stress rather than ondecreased effective stress during development. The experimental resultsshow that the relationship between intrinsic permeability and effectivestress in reservoirs in general follows a quadratic polynomial functionalform, found to best capture how effective stress influences formationpermeability. In addition, this experimental study reveals that changesin formation permeability, caused by both elastic and plasticdeformation, are permanent and irreversible. Related pore-deformationtests using electronic microscope scanning and constant-rate mercuryinjection techniques show that while stress variation generally has smallimpact onrock porosity, the size and shape of pore throats have asignificant impact on permeability-stress sensitivity. Based on the testresults and theoretical analyses, we believe that there exists a cone ofpressure depression in the area near production within suchstress-sensitive tight reservoirs, leading to a low-permeability zone,and that well production will decrease under the influence of stresssensitivity.
Date: August 28, 2007
Creator: Lei, Qun; Xiong, Wei; Yuan, Cui & Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

Enhancing Scalability and Efficiency of the TOUGH2_MP for LinuxClusters

Description: TOUGH2{_}MP, the parallel version TOUGH2 code, has been enhanced by implementing more efficient communication schemes. This enhancement is achieved through reducing the amount of small-size messages and the volume of large messages. The message exchange speed is further improved by using non-blocking communications for both linear and nonlinear iterations. In addition, we have modified the AZTEC parallel linear-equation solver to nonblocking communication. Through the improvement of code structuring and bug fixing, the new version code is now more stable, while demonstrating similar or even better nonlinear iteration converging speed than the original TOUGH2 code. As a result, the new version of TOUGH2{_}MP is improved significantly in its efficiency. In this paper, the scalability and efficiency of the parallel code are demonstrated by solving two large-scale problems. The testing results indicate that speedup of the code may depend on both problem size and complexity. In general, the code has excellent scalability in memory requirement as well as computing time.
Date: April 17, 2006
Creator: Zhang, Keni & Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

A comparison of analytical approaches for wellbore heat transmission in layered formations

Description: This report presents an analytical method for determining wellbore heat transmission during liquid or gas flow along the tubing. The mathematical model describes the heat transfer between the flowing fluid in the wellbore and in the surrounding formation as one whole physical system. The transient heat transfer equations in the two regions with coupling at the sandface are solved simultaneously. Non-homogeneous formations are treated which consist of several layers with different physical properties and arbitrary initial temperature distributions in the vertical direction. Closed form analytical solutions are obtained in real space and in Laplace space, which can be used to calculate the temperature distribution along the wellbore and in the formation, and to evaluate heat transfer rate and cumulative heat exchange between wellbore and formation. A more accurate formula is given for the widely-used transient heat conduction function f(t{sub D}) of thermal resistance. 14 refs., 12 figs., 1 tab.
Date: August 1, 1988
Creator: Wu, Yu-Shu.
Partner: UNT Libraries Government Documents Department

Analyzing flow patterns in unsaturated fractured rock of YuccaMountain using an integrated modeling approach

Description: This paper presents a series of modeling investigations to characterize percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. The investigations are conducted using a modeling approach that integrates a wide variety of moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model through model calibration. This integrated modeling approach, based on a dual-continuum formulation, takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain's highly heterogeneous, unsaturated fractured tuffs. In particular, the model results are examined against different types of field-measured data and used to evaluate different hydrogeological conceptual models and their effects on flow patterns in the unsaturated zone. The objective of this work to provide understanding of percolation patterns and flow behavior through the unsaturated zone, which is a crucial issue in assessing repository performance.
Date: November 3, 2003
Creator: Wu, Yu-Shu; Lu, Guoping; Zhang, Keni; Pan, Lehua & Bodvarsson,Gudmundur S.
Partner: UNT Libraries Government Documents Department

An integrated methodology for characterizing flow and transportprocesses in fractured rock

Description: To investigate the coupled processes involved in fluid andheat flow and chemical transport in the highly heterogeneous,unsaturated-zone (UZ) fractured rock of Yucca Mountain, we present anintegrated modeling methodology. This approach integrates a wide varietyof moisture, pneumatic, thermal, and geochemical isotopic field data intoa comprehensive three-dimensional numerical model for modeling analyses.The results of field applications of the methodology show that moisturedata, such as water potential and liquid saturation, are not sufficientto determine in situ percolation flux, whereas temperature andgeochemical isotopic data provide better constraints to net infiltrationrates and flow patterns. In addition, pneumatic data are found to beextremely valuable in estimating large-scale fracture permeability. Theintegration of hydrologic, pneumatic, temperature, and geochemical datainto modeling analyses is thereby demonstrated to provide a practicalmodeling approachfor characterizing flow and transport processes incomplex fractured formations.
Date: August 31, 2007
Creator: Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

Fracture-Flow-Enhanced Solute Diffusion into Fractured Rock

Description: We propose a new conceptual model of fracture-flow-enhanced matrix diffusion, which correlates with fracture-flow velocity, i.e., matrix diffusion enhancement induced by rapid fluid flow within fractures. According to the boundary-layer or film theory, fracture flow enhanced matrix diffusion may dominate mass-transfer processes at fracture-matrix interfaces, because rapid flow along fractures results in large velocity and concentration gradients at and near fracture-matrix interfaces, enhancing matrix diffusion at matrix surfaces. In this paper, we present a new formulation of the conceptual model for enhanced fracture-matrix diffusion, and its implementation is discussed using existing analytical solutions and numerical models. In addition, we use the enhanced matrix diffusion concept to analyze laboratory experimental results from nonreactive and reactive tracer breakthrough tests, in an effort to validate the new conceptual model.
Date: December 15, 2007
Creator: Wu, Yu-Shu; Ye, Ming & Sudicky, E.A.
Partner: UNT Libraries Government Documents Department

Efficient parallel simulation of CO2 geologic sequestration insaline aquifers

Description: An efficient parallel simulator for large-scale, long-termCO2 geologic sequestration in saline aquifers has been developed. Theparallel simulator is a three-dimensional, fully implicit model thatsolves large, sparse linear systems arising from discretization of thepartial differential equations for mass and energy balance in porous andfractured media. The simulator is based on the ECO2N module of the TOUGH2code and inherits all the process capabilities of the single-CPU TOUGH2code, including a comprehensive description of the thermodynamics andthermophysical properties of H2O-NaCl- CO2 mixtures, modeling singleand/or two-phase isothermal or non-isothermal flow processes, two-phasemixtures, fluid phases appearing or disappearing, as well as saltprecipitation or dissolution. The new parallel simulator uses MPI forparallel implementation, the METIS software package for simulation domainpartitioning, and the iterative parallel linear solver package Aztec forsolving linear equations by multiple processors. In addition, theparallel simulator has been implemented with an efficient communicationscheme. Test examples show that a linear or super-linear speedup can beobtained on Linux clusters as well as on supercomputers. Because of thesignificant improvement in both simulation time and memory requirement,the new simulator provides a powerful tool for tackling larger scale andmore complex problems than can be solved by single-CPU codes. Ahigh-resolution simulation example is presented that models buoyantconvection, induced by a small increase in brine density caused bydissolution of CO2.
Date: January 1, 2007
Creator: Zhang, Keni; Doughty, Christine; Wu, Yu-Shu & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

EOS3nn: An iTOUGH2 module for non-Newtonian liquid and gasflow

Description: This report documents the iTOUGH2 module EOS3nn, developed for modeling two-phase isothermal flow of a non-Newtonian liquid and a non-condensible gas in multidimensional, porous and fractured geologic media. This document supplements the TOUGH2 and iTOUGH2 user s guides and is therefore not a self-contained manual. It presents information on the physical processes modeled and the mathematical and numerical methods used. Also included are two sample problems for code testing and benchmarking. Modeling scenarios and approaches are discussed to illustrate problem setup and usage of the EOS3nn module.
Date: August 1, 2002
Creator: Wu, Yu-Shu; Finsterle, Stefan & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Modeling Hydraulic Responses to Meteorological Forcing: fromCanopy to Aquifer

Description: An understanding of the hydrologic interactions amongatmosphere, land surface, and subsurface is one of the keys tounderstanding the water cycling system that supports our life system onearth. Properly modeling such interactionsis a difficult task because oftheinherent coupled processes and complex feedback structures amongsubsystems. In this paper, we present a model that simulates thelandsurface and subsurface hydrologic response to meteorological forcing.This model combines a state of the art landsurface model, the NCARCommunity Land Model version 3 (CLM3), with a variablysaturatedgroundwater model, the TOUGH2, through an internal interfacethat includes flux and state variables shared by the two submodels.Specifically, TOUGH2, in its simulation, uses infiltration, evaporation,and rootuptake rates, calculated by CLM3, as source/sink terms? CLM3, inits simulation, uses saturation and capillary pressure profiles,calculated by TOUGH2, as state variables. This new model, CLMT2,preserves the best aspects of both submodels: the state of the artmodeling capability of surface energy and hydrologic processes from CLM3and the more realistic physical process based modeling capability ofsubsurface hydrologic processes from TOUGH2. The preliminary simulationresults show that the coupled model greatly improves the predictions ofthe water table, evapotranspiration, surface temperature, and moisture inthe top 20 cm of soil at a real watershed, as evaluated from 18 years ofobserved data. The new model is also ready to be coupled with anatmospheric simulation model, representing one of the first models thatare capable to simulate hydraulic processes from top of the atmosphere todeep ground.
Date: February 8, 2007
Creator: Pan, Lehua; Jin, Jiming; Miller, Norman; Wu, Yu-Shu & Bodvarsson,Gudmundur
Partner: UNT Libraries Government Documents Department

Characterizing two-phase flow relative permeabilities in chemicalflooding using a pore-scale network model

Description: A dynamic pore-scale network model is presented for investigating the effects of interfacial tension and oil-water viscosity on relative permeability during chemical flooding. This model takes into account both viscous and capillary forces in analyzing the impact of chemical properties on flow behavior or displacement configuration, as opposed to the conventional or invasion percolation algorithm which incorporates capillary pressure only. The study results indicate that both water and oil relative-permeability curves are dependent strongly on interfacial tension as well as an oil-water viscosity ratio. In particular, water and oil relative-permeability curves are both found to shift upward as interfacial tension is reduced, and they both tend to become linear versus saturation once interfacial tension is at low values. In addition, the oil-water viscosity ratio appears to have only a small effect under conditions of high interfacial tension. When the interfacial tension is low, however, water relative permeability decreases more rapidly (with the increase in the aqueous-phase viscosity) than oil relative permeability. The breakthrough saturation of the aqueous phase during chemical flooding tends to decrease with the reduction of interfacial tension and may also be affected by the oil-water viscosity ratio.
Date: March 15, 2004
Creator: Liu, Qingjie; Shen, Pingping & Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

Efficient Schemes for Reducing Numerical Dispersion in ModelingMultiphase Transport through Porous and Fractured Media

Description: Numerical issues with modeling transport of chemicals or solute in realistic large-scale subsurface systems have been a serious concern, even with the continual progress made in both simulation algorithms and computer hardware in the past few decades. The problem remains and becomes even more difficult when dealing with chemical transport in a multiphase flow system using coarse, multidimensional regular or irregular grids, because of the known effects of numerical dispersion associated with moving plume fronts. We have investigated several total-variation-diminishing (TVD) or flux-limiter schemes by implementing and testing them in the T2R3D code, one of the TOUGH2 family of codes. The objectives of this paper are (1) to investigate the possibility of applying these TVD schemes, using multi-dimensional irregular unstructured grids, and (2) to help select more accurate spatial averaging methods for simulating chemical transport given a numerical grid or spatial discretization. We present an application example to show that such TVD schemes are able to effectively reduce numerical dispersion.
Date: April 13, 2006
Creator: Wu, Yu-Shu & Forsyth, Peter A.
Partner: UNT Libraries Government Documents Department

Development of Hydrologic Characterization Technology of Fault Zones

Description: Through an extensive literature survey we find that there is very limited amount of work on fault zone hydrology, particularly in the field using borehole testing. The common elements of a fault include a core, and damage zones. The core usually acts as a barrier to the flow across it, whereas the damage zone controls the flow either parallel to the strike or dip of a fault. In most of cases the damage zone isthe one that is controlling the flow in the fault zone and the surroundings. The permeability of damage zone is in the range of two to three orders of magnitude higher than the protolith. The fault core can have permeability up to seven orders of magnitude lower than the damage zone. The fault types (normal, reverse, and strike-slip) by themselves do not appear to be a clear classifier of the hydrology of fault zones. However, there still remains a possibility that other additional geologic attributes and scaling relationships can be used to predict or bracket the range of hydrologic behavior of fault zones. AMT (Audio frequency Magneto Telluric) and seismic reflection techniques are often used to locate faults. Geochemical signatures and temperature distributions are often used to identify flow domains and/or directions. ALSM (Airborne Laser Swath Mapping) or LIDAR (Light Detection and Ranging) method may prove to be a powerful tool for identifying lineaments in place of the traditional photogrammetry. Nonetheless not much work has been done to characterize the hydrologic properties of faults by directly testing them using pump tests. There are some uncertainties involved in analyzing pressure transients of pump tests: both low permeability and high permeability faults exhibit similar pressure responses. A physically based conceptual and numerical model is presented for simulating fluid and heat flow and solute transport through fractured fault zones ...
Date: March 31, 2008
Creator: Karasaki, Kenzi; Onishi, Tiemi & Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

User's Guide for TOUGH2-MP - A Massively Parallel Version of the TOUGH2 Code

Description: TOUGH2-MP is a massively parallel (MP) version of the TOUGH2 code, designed for computationally efficient parallel simulation of isothermal and nonisothermal flows of multicomponent, multiphase fluids in one, two, and three-dimensional porous and fractured media. In recent years, computational requirements have become increasingly intensive in large or highly nonlinear problems for applications in areas such as radioactive waste disposal, CO2 geological sequestration, environmental assessment and remediation, reservoir engineering, and groundwater hydrology. The primary objective of developing the parallel-simulation capability is to significantly improve the computational performance of the TOUGH2 family of codes. The particular goal for the parallel simulator is to achieve orders-of-magnitude improvement in computational time for models with ever-increasing complexity. TOUGH2-MP is designed to perform parallel simulation on multi-CPU computational platforms. An earlier version of TOUGH2-MP (V1.0) was based on the TOUGH2 Version 1.4 with EOS3, EOS9, and T2R3D modules, a software previously qualified for applications in the Yucca Mountain project, and was designed for execution on CRAY T3E and IBM SP supercomputers. The current version of TOUGH2-MP (V2.0) includes all fluid property modules of the standard version TOUGH2 V2.0. It provides computationally efficient capabilities using supercomputers, Linux clusters, or multi-core PCs, and also offers many user-friendly features. The parallel simulator inherits all process capabilities from V2.0 together with additional capabilities for handling fractured media from V1.4. This report provides a quick starting guide on how to set up and run the TOUGH2-MP program for users with a basic knowledge of running the (standard) version TOUGH2 code, The report also gives a brief technical description of the code, including a discussion of parallel methodology, code structure, as well as mathematical and numerical methods used. To familiarize users with the parallel code, illustrative sample problems are presented.
Date: May 27, 2008
Creator: Zhang, Keni; Zhang, Keni; Wu, Yu-Shu & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

A 3-D hydrodynamic dispersion model for modeling tracer transport in Geothermal Reservoirs

Description: A 3-D hydrodynamic dispersion model for tracer transport is developed and implemented into the TOUGH2 EOS3 (T2R3D) module. The model formulation incorporates a full dispersion tensor, based on a 3-D velocity field with a 3-D, irregular grid in a heterogeneous geological system. Two different weighting schemes are proposed for spatial average of 3-D velocity fields and concentration gradients to evaluate the mass flux by dispersion and diffusion of a tracer or a radionuclide. This new module of the TOUGH2 code is designed to simulate processes of tracer/radionuclide transport using an irregular, 3-D integral finite difference grid in non-isothermal, three-dimensional, multiphase, porous/fractured subsurface systems. The numerical method for this transport module is based on the integral finite difference scheme, as in the TOUGH2 code. The major assumptions of the tracer transport module are: (a) a tracer or a radionuclide is present and transported only within the liquid phase, (b) transport mechanisms include molecular diffusion and hydrodynamic dispersion in the liquid phase in addition to advection, and (c) first order decay and linear adsorption on rock grains are taken into account. The tracer or radionuclide is introduced as an additional mass component into the standard TOUGH2 formulation, time is discretized fully implicitly, and non-linearities of the conservation equations are handled using the Newton/Raphson iteration. We have verified this transport module by comparison with results of a 2-D transport problem for which an analytical solution is available. In addition, a field application is described to demonstrate the use of the proposed model.
Date: January 26, 1998
Creator: Wu, Yu-Shu & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

An analytical solution for transient radial flow through unsaturated fractured porous media

Description: This paper presents analytical solutions for one-dimensional radial transient flow through horizontal, unsaturated fractured rock formation. In these solutions, unsaturated flow through fractured media is described by a linearized Richards' equation, while fracture-matrix interaction is handled using the dual-continuum concept. Although linearizing Richards' equation requires a specially correlated relationship between relative permeability and capillary pressure functions for both fractures and matrix, these specially formed relative permeability and capillary pressure functions are still physically meaningful. These analytical solutions can thus be used to describe the transient behavior of unsaturated flow in fractured media under the described model conditions. They can also be useful in verifying numerical simulation results, which, as demonstrated in this paper, are otherwise difficult to validate.
Date: February 13, 2004
Creator: Wu, Yu-Shu & Pan, Lehua
Partner: UNT Libraries Government Documents Department

Temporal Damping Effect of the Yucca Mountain FracturedUnsaturated Rock on Transient Infiltration Pulses

Description: Performance assessment of the Yucca Mountain unsaturated zone (UZ) as the site for an underground repository of high-level radioactive waste relies on the crucial assumption that water percolation processes in the unsaturated zone can be approximated as a steady-state condition. Justification of such an assumption is based on temporal damping effects of several geological units within the unsaturated tuff formation. In particular, the nonwelded tuff of the Painbrush Group (PTn unit) at Yucca Mountain, because of its highly porous physical properties, has been conceptualized to have a significant capacity for temporally damping transient percolation fluxes. The objective of this study is to investigate these damping effects, using a three-dimensional (3-D) mountain-scale model as well as several one-dimensional (1-D) models. The 3-D model incorporates a wide variety of the updated field data for the highly heterogeneous unsaturated formation at Yucca Mountain. The model is first run to steady state and calibrated using field-measured data and then transient pulse infiltrations are applied to the model top boundary. Subsequent changes in percolation fluxes at the bottom of and within the PTn unit are examined under episodic infiltration boundary conditions. The 1-D model is used to examine the long-term response of the flow system to higher infiltration pulses, while the damping effect is also investigated through modeling tracer transport in the UZ under episodic infiltration condition. Simulation results show the existence of damping effects within the PTn unit and also indicate that the assumption of steady-state flow conditions below the PTn unit is reasonable. However, the study also finds that some fast flow paths along faults exist, causing vertical-flux quick responses at the PTn bottom to the episodic infiltration at the top boundary.
Date: May 2, 2005
Creator: Zhang, Keni; Wu, Yu-Shu & Pan, Lehua
Partner: UNT Libraries Government Documents Department

A Physically Based Approach for Modeling Multiphase Fracture-Matrix Interaction in Fractured Porous Media

Description: Modeling fracture-matrix interaction within a complex multiple phase flow system is a key issue for fractured reservoir simulation. Commonly used mathematical models for dealing with such interactions employ a dual- or multiple-continuum concept, in which fractures and matrix are represented as overlapping, different, but interconnected continua, described by parallel sets of conservation equations. The conventional single-point upstream weighting scheme, in which the fracture relative permeability is used to represent the counterpart at the fracture-matrix interface, is the most common scheme by which to estimate flow mobility for fracture-matrix flow terms. However, such a scheme has a serious flaw, which may lead to unphysical solutions or significant numerical errors. To overcome the limitation of the conventional upstream weighting scheme, this paper presents a physically based modeling approach for estimating physically correct relative permeability in calculating multiphase flow between fractures and the matrix, using continuity of capillary pressure at the fracture-matrix interface. The proposed approach has been implemented into two multiphase reservoir simulators and verified using analytical solutions and laboratory experimental data. The new method is demonstrated to be accurate, numerically efficient, and easy to implement in dual- or multiple-continuum models.
Date: March 15, 2004
Creator: Wu, Yu-Shu; Pan, Lehua & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Application of parallel computing techniques to a large-scale reservoir simulation

Description: Even with the continual advances made in both computational algorithms and computer hardware used in reservoir modeling studies, large-scale simulation of fluid and heat flow in heterogeneous reservoirs remains a challenge. The problem commonly arises from intensive computational requirement for detailed modeling investigations of real-world reservoirs. This paper presents the application of a massive parallel-computing version of the TOUGH2 code developed for performing large-scale field simulations. As an application example, the parallelized TOUGH2 code is applied to develop a three-dimensional unsaturated-zone numerical model simulating flow of moisture, gas, and heat in the unsaturated zone of Yucca Mountain, Nevada, a potential repository for high-level radioactive waste. The modeling approach employs refined spatial discretization to represent the heterogeneous fractured tuffs of the system, using more than a million 3-D gridblocks. The problem of two-phase flow and heat transfer within the model domain leads to a total of 3,226,566 linear equations to be solved per Newton iteration. The simulation is conducted on a Cray T3E-900, a distributed-memory massively parallel computer. Simulation results indicate that the parallel computing technique, as implemented in the TOUGH2 code, is very efficient. The reliability and accuracy of the model results have been demonstrated by comparing them to those of small-scale (coarse-grid) models. These comparisons show that simulation results obtained with the refined grid provide more detailed predictions of the future flow conditions at the site, aiding in the assessment of proposed repository performance.
Date: February 1, 2001
Creator: Zhang, Keni; Wu, Yu-Shu; Ding, Chris & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

On the Effective Continuum Method for Modeling MultiphaseFlow, Multicomponent Transport and Heat Transfer in FracturedRock

Description: Flow and transport through fractured porous media occurs in many subsurface systems and has received considerable attention in recent years due to the importance in the areas of underground natural resource recovery, waste storage, and environmental remediation scheme. Among the methods of handling fracture/matrix flow and transport through geological media, the effective continuum method (ECM) has been widely used, and misused in some cases, because of its simplicity in terms of data requirements and computational efficiency. This paper presents a rigorous, generalized effective continuum formulation, which has been implemented into the TOUGH2 code (Pruess, 1991) for modeling multiphase, multicomponent, non-isothermal flow and transport in fractured rocks. Also included in the paper are discussions of the conditions under which the ECM approach applies and the procedures for evaluating the effective parameters for both flow and transport simulations. Three application examples, one multiphase flow, one heat flow and one chemical transport problem, are given to demonstrate the usefulness of the ECM method.
Date: January 1, 1999
Creator: Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

A unified numerical framework model for simulating flow, transport, and heat transfer in porous and fractured media

Description: It has long been recognized that a common ground exists between governing equations used for describing various flow and transport phenomena in porous media. Put another way they are all generally based on the same form of mass and/or energy conservation laws. This implies that there may exist a unified formulation and numerical scheme applicable to modeling all of these physical processes. This paper explores such a possibility and proposes a generalized framework, as well as a mathematical formulation for modeling all known transport phenomena in porous media. Based on this framework, a unified numerical approach is developed and tested using multidimensional, multiphase flow, isothermal and nonisothermal reservoir simulators. In this approach, a spatial domain of interest is discretized with an unstructured grid, then a time discretization is carried out with a backward, first-order, finite-difference method. The final discrete nonlinear equations are handled fully implicitly, using Newton iteration. In addition, the fracture medium is handled using a general dual-continuum concept with continuum or discrete modeling methods. A number of applications are discussed to demonstrate that with this unified approach, modeling a particular porous-medium flow and transport process simply becomes a matter of defining a set of state variables, along with their interrelations or mutual influence.
Date: February 13, 2004
Creator: Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

The Influence of Repository Thermal Load on Multiphase Flow and Heat Transfer in the Unsaturated Zone of Yucca Mountain

Description: The 500-700 m thick Yucca Mountain unsaturated zone (UZ) is under extensive investigation as a subsurface repository for the permanent disposal of high-level nuclear wastes. The site characterization has been mostly carried out for analyzing unsaturated flow and radionuclide transport under ambient, isothermal conditions. However, significant research effort has also been devoted to understand the nature of flow and transport processes under non-isothermal conditions. In particular, substantial repository heating from radioactive waste decay has motivated investigations of the coupled thermo-hydrologic (TH) behavior of the UZ under repository heating and its potential impact on repository performance. Significant progress has been made in quantitative coupled TH studies in the last decade. Despite the significant advances made so far in modeling and understanding TH processes, the previous studies have been in general limited to modeling in 1-D and 2-D (instead of the full 3-D representation), and/or small spatial and temporal scale analysis. In addition to these limited modeling exercises, multidimensional modeling has been carried out for large-scale (at the scale of the entire mountain) TH analyses. However, these previous large, mountain-scale TH models utilized the effective continuum model (ECM), rather than the more rigorous dual-continuum model (DKM). This is primarily due to numerical difficulties and computational burden involved with simulating highly non-linear coupled two-phase fluid flow and heat transfer in the fractured unsaturated rock with over one hundred thousand grid blocks (required for mountain-scale simulations). In general, 3-D, mountain-scale, DKM investigations of coupled TH processes in the fractured rock of Yucca Mountain is lacking in the literature. In parallel to the TH modeling studies, significant progress has also been made in site characterization of UZ flow and transport processes. For example, field and modeling studies conducted over the past few years have updated and enhanced our understanding, and revealed many new insights into ...
Date: February 14, 2005
Creator: Wu, Yu-Shu; Mukhopadhyay, S.; Zhang, K. & Bodvarsson, G.S.
Partner: UNT Libraries Government Documents Department

Non-darcy flow behavior mean high-flux injection wells in porous and fractured formations

Description: This paper presents a study of non-Darcy fluid flow through porous and fractured rock, which may occur near wells during high-flux injection of waste fluids into underground formations. Both numerical and analytical models are used in this study. General non-Darcy flow is described using the Forchheimer equation, implemented in a three-dimensional, multiphase flow reservoir simulator. The non-Darcy flow through a fractured reservoir is handled using a general dual continuum approach, covering commonly used conceptual models, such as double porosity, dual permeability, explicit fracture, etc. Under single-phase flow conditions, an approximate analytical solution, as an extension of the Warren-Root solution, is discussed. The objectives of this study are (1) to obtain insights into the effect of non-Darcy flow on transient pressure behavior through porous and fractured reservoirs and (2) to provide type curves for well test analyses of non-Darcy flow wells. The type curves generated include various types of drawdown, injection, and buildup tests with non-Darcy flow occurring in porous and fractured reservoirs. In addition, non-Darcy flow into partially penetrating wells is also considered. The transient-pressure type curves for flow in fractured reservoirs are based on the double-porosity model. Type curves provided in this work for non-Darcy flow in porous and fractured reservoirs will find their applications in well test interpretation using a type-curve matching technique.
Date: April 25, 2003
Creator: Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department