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The effect of unheated sections on moisture transport in theemplacement drift

Description: A thermal-hydrologic-natural-ventilation model is configuredfor simulating temperature, humidity, and condensate distributions in thecoupled domains of the in-drift airspace and the near-field rockmass.Meaningful results are obtained from the model for a practicalapplication in which the beneficial effects of unheated drift sectionsare analyzed. Sensitivity to the axial dispersion coefficient is alsostudied with the model.
Date: September 1, 2005
Creator: Danko, G.; Birkholzer, J. & Barahmi, D.
Partner: UNT Libraries Government Documents Department

Estimating Liquid Fluxes in Thermally Perturbed Fractured Rock Using Measured Temperature Profiles

Description: A new temperature-profile method was recently developed for analyzing perturbed flow conditions in superheated porous media. The method uses high-resolution temperature data to estimate the magnitude of the heat-driven liquid and gas fluxes that form as a result of boiling, condensation, and recirculation of pore water. In this paper, we evaluate the applicability of this new method to the more complex flow behavior in fractured formations with porous rock matrix. In such formations, with their intrinsic heterogeneity, the porous but low-permeable matrix provides most of the mass and heat storage capacity, and dominates conductive heat transfer, Fractures, on the other hand, offer highly effective conduits for gas and liquid flow, thereby generating significant convective heat transfer. After establishing the accuracy of the temperature-profile method for fractured porous formations, we apply the method in analyzing the perturbed flow conditions in a large-scale underground heater test conducted in unsaturated fractured porous tuff. The flux estimates for this test indicate a significant reflux of water near the heat source, on the order of a few hundred millimeter per year-much larger than the ambient percolation flux of only a few millimeter per year.
Date: February 14, 2005
Creator: Birkholzer, J.T.
Partner: UNT Libraries Government Documents Department

Abstraction of Drift Seepage

Description: This model report documents the abstraction of drift seepage, conducted to provide seepage-relevant parameters and their probability distributions for use in Total System Performance Assessment for License Application (TSPA-LA). Drift seepage refers to the flow of liquid water into waste emplacement drifts. Water that seeps into drifts may contact waste packages and potentially mobilize radionuclides, and may result in advective transport of radionuclides through breached waste packages [''Risk Information to Support Prioritization of Performance Assessment Models'' (BSC 2003 [DIRS 168796], Section 3.3.2)]. The unsaturated rock layers overlying and hosting the repository form a natural barrier that reduces the amount of water entering emplacement drifts by natural subsurface processes. For example, drift seepage is limited by the capillary barrier forming at the drift crown, which decreases or even eliminates water flow from the unsaturated fractured rock into the drift. During the first few hundred years after waste emplacement, when above-boiling rock temperatures will develop as a result of heat generated by the decay of the radioactive waste, vaporization of percolation water is an additional factor limiting seepage. Estimating the effectiveness of these natural barrier capabilities and predicting the amount of seepage into drifts is an important aspect of assessing the performance of the repository. The TSPA-LA therefore includes a seepage component that calculates the amount of seepage into drifts [''Total System Performance Assessment (TSPA) Model/Analysis for the License Application'' (BSC 2004 [DIRS 168504], Section 6.3.3.1)]. The TSPA-LA calculation is performed with a probabilistic approach that accounts for the spatial and temporal variability and inherent uncertainty of seepage-relevant properties and processes. Results are used for subsequent TSPA-LA components that may handle, for example, waste package corrosion or radionuclide transport.
Date: November 1, 2004
Creator: Birkholzer, J.T.
Partner: UNT Libraries Government Documents Department

A Temperature-Profile Method for Estimating Flow Processes in Geologic Heat Pipes

Description: Above-boiling temperature conditions, as encountered, for example, in geothermal reservoirs and in geologic repositories for the storage of heat-producing nuclear wastes, may give rise to strongly altered liquid and gas flow processes in porous subsurface environments. The magnitude of such flow perturbation is extremely hard to measure in the field. We therefore propose a simple temperature-profile method that uses high-resolution temperature data for deriving such information. The energy that is transmitted with the vapor and water flow creates a nearly isothermal zone maintained at about the boiling temperature, referred to as a heat pipe. Characteristic features of measured temperature profiles, such as the differences in the gradients inside and outside of the heat pipe regions, are used to derive the approximate magnitude of the liquid and gas fluxes in the subsurface, for both steady-state and transient conditions.
Date: January 21, 2005
Creator: Birkholzer, J.T.
Partner: UNT Libraries Government Documents Department

TH{_}PULSE Program for Calculating Infiltration of Episodic Liquid Fingers in Superheated Rock Fractures

Description: This report describes the code TH{_}PULSE developed at the Ernest Orlando Lawrence Berkeley National Laboratory (Berkeley Lab). The code handles gravity-driven flow of episodic infiltration events entering above-boiling rock-temperature regions. Such temperature conditions are expected, for example, after emplacement of heat-generating nuclear waste in underground repositories. Complex fluid-flow and heat-transfer phenomena occur, as the infiltrating water is subject to vigorous boiling from the hot rock. A new efficient semi-analytical method is presented herein that simulates such phenomena. It is assumed that flow forms in localized preferential flow paths (referred to as ''fingers''). The first section of this report gives the conceptual and mathematical background for the solution scheme. The second section is a user's manual for TH{_}PULSE, providing all information required to run the code, including a detailed description of the input and output files. In the third section, the new solution scheme is applied to several test cases. Sample simulations are performed for conditions representative of the potential nuclear waste repository at Yucca Mountain, Nevada. A brief summary is given in Section 4.
Date: June 1, 2002
Creator: Birkholzer, J.T.
Partner: UNT Libraries Government Documents Department

The Effect of Unheated Sections on Moisture Transport in the Emplacement Drift

Description: The goals of this study are: (1) to configure a thermal-hydrological, natural-ventilation model for simulating temperature, humidity, and condensate distributions in the coupled domains of in-drift airspace and near-field rockmass. Rokmass model: TOUGH2, in-drift model: MULTIFLUX (MF); (2) obtain meaningful results from the model for a practical application in which the beneficial effects of unheated drift sections are analyzed; and (3) study the sensitivity to the axial dispersion coefficient with the model.
Date: April 27, 2006
Creator: Danko, G.; Birkholzer, J. & Bahrami, D.
Partner: UNT Libraries Government Documents Department

The effect of unheated sections on moisture transport in theemplacement drift

Description: A thermal-hydrologic-natural-ventilation model is configuredfor simulating temperature, humidity, and condensate distributions in thecoupled domains of the in-drift airspace and the near-field rockmass.Meaningful results are obtained from the model for a practicalapplication in which the beneficial effects of unheated drift sectionsare analyzed. Sensitivity to the axial dispersion coefficient is alsostudied with the model.
Date: September 1, 2005
Creator: Danko, G.; Birkholzer, J. & Barahmi, D.
Partner: UNT Libraries Government Documents Department

DRIFT-SCALE COUPLED PROCESSES (DST AND TH SEEPAGE) MODELS

Description: The purpose of this report is to document drift-scale modeling work performed to evaluate the thermal-hydrological (TH) behavior in Yucca Mountain fractured rock close to waste emplacement drifts. The heat generated by the decay of radioactive waste results in rock temperatures elevated from ambient for thousands of years after emplacement. Depending on the thermal load, these temperatures are high enough to cause boiling conditions in the rock, giving rise to water redistribution and altered flow paths. The predictive simulations described in this report are intended to investigate fluid flow in the vicinity of an emplacement drift for a range of thermal loads. Understanding the TH coupled processes is important for the performance of the repository because the thermally driven water saturation changes affect the potential seepage of water into waste emplacement drifts. Seepage of water is important because if enough water gets into the emplacement drifts and comes into contact with any exposed radionuclides, it may then be possible for the radionuclides to be transported out of the drifts and to the groundwater below the drifts. For above-boiling rock temperatures, vaporization of percolating water in the fractured rock overlying the repository can provide an important barrier capability that greatly reduces (and possibly eliminates) the potential of water seeping into the emplacement drifts. In addition to this thermal process, water is inhibited from entering the drift opening by capillary forces, which occur under both ambient and thermal conditions (capillary barrier). The combined barrier capability of vaporization processes and capillary forces in the near-field rock during the thermal period of the repository is analyzed and discussed in this report.
Date: January 13, 2005
Creator: Birkholzer, J.T. & Mukhopadhyay, S.
Partner: UNT Libraries Government Documents Department

Coupled In-Rock and In-Drift Hydrothermal Model Stuudy For Yucca Mountain

Description: A thermal-hydrologic-natural-ventilation model is configured for simulating temperature, humidity, and condensate distributions in the coupled domains of the in-drift airspace and the near-field rockmass in the proposed Yucca Mountain repository. The multi-physics problem is solved with MULTIFLUX in which a lumped-parameter computational fluid dynamics model is iterated with TOUGH2. The solution includes natural convection, conduction, and radiation for heat as well as moisture convection and diffusion for moisture transport with half waste package scale details in the drift, and mountain-scale heat and moisture transport in the porous and fractured rock-mass. The method provides fast convergence on a personal computer computational platform. Numerical examples and comparison with a TOUGH2 based, integrated model are presented.
Date: December 18, 2006
Creator: Danko, G.; Birkholzer, J. & Bahrami, D.
Partner: UNT Libraries Government Documents Department

Disposal R&D in the Used Fuel Disposition Campaign: A Discussion of Opportunities for Active International Collaboration

Description: For DOE's Used Fuel Disposition Campaign (UFDC), international collaboration is a beneficial and cost-effective strategy for advancing disposal science with regards to multiple disposal options and different geologic environments. While the United States disposal program focused solely on Yucca Mountain tuff as host rock over the past decades, several international programs have made significant progress in the characterization and performance evaluation of other geologic repository options, most of which are very different from the Yucca Mountain site in design and host rock characteristics. Because Yucca Mountain was so unique (e.g., no backfill, unsaturated densely fractured tuff), areas of direct collaboration with international disposal programs were quite limited during that time. The decision by the U.S. Department of Energy to no longer pursue the disposal of high-level radioactive waste and spent fuel at Yucca Mountain has shifted UFDC's interest to disposal options and geologic environments similar to those being investigated by disposal programs in other nations. Much can be gained by close collaboration with these programs, including access to valuable experience and data collected over recent decades. Such collaboration can help to efficiently achieve UFDC's long-term goals of conducting 'experiments to fill data needs and confirm advanced modeling approaches' (by 2015) and of having a 'robust modeling and experimental basis for evaluation of multiple disposal system options' (by 2020). This report discusses selected opportunities of active international collaboration, with focus on both Natural Barrier System (NBS) and Engineered Barrier System (EBS) aspects and those opportunities that provide access to field data (and respective interpretation/modeling) or allow participation in ongoing field experiments. This discussion serves as a basis for the DOE/NE-53 and UFDC planning process for FY12 and beyond.
Date: June 1, 2011
Creator: Birkholzer, J. T.
Partner: UNT Libraries Government Documents Department

Drift-Scale Coupled Processes (DST and TH Seepage) Models

Description: The purpose of this report is to document drift-scale modeling work performed to evaluate the thermal-hydrological (TH) behavior in Yucca Mountain fractured rock close to waste emplacement drifts. The heat generated by the decay of radioactive waste results in rock temperatures elevated from ambient for thousands of years after emplacement. Depending on the thermal load, these temperatures are high enough to cause boiling conditions in the rock, giving rise to water redistribution and altered flow paths. The predictive simulations described in this report are intended to investigate fluid flow in the vicinity of an emplacement drift for a range of thermal loads. Understanding the TH coupled processes is important for the performance of the repository because the thermally driven water saturation changes affect the potential seepage of water into waste emplacement drifts. Seepage of water is important because if enough water gets into the emplacement drifts and comes into contact with any exposed radionuclides, it may then be possible for the radionuclides to be transported out of the drifts and to the groundwater below the drifts. For above-boiling rock temperatures, vaporization of percolating water in the fractured rock overlying the repository can provide an important barrier capability that greatly reduces (and possibly eliminates) the potential of water seeping into the emplacement drifts. In addition to this thermal process, water is inhibited from entering the drift opening by capillary forces, which occur under both ambient and thermal conditions (capillary barrier). The combined barrier capability of vaporization processes and capillary forces in the near-field rock during the thermal period of the repository is analyzed and discussed in this report.
Date: September 29, 2004
Creator: Birkholzer, J. & Mukhopadhyay, S.
Partner: UNT Libraries Government Documents Department

Modeling a Thermal Seepage Laboratory Experiment

Description: A thermal seepage model has been developed to evaluate the potential for seepage into the waste emplacement drifts at the proposed high-level radioactive materials repository at Yucca Mountain when the rock is at elevated temperature. The coupled-process-model results show that no seepage occurs as long as the temperature at the drift wall is above boiling. This important result has been incorporated into the Total System Performance Assessment of Yucca Mountain. We have applied the same conceptual model to a laboratory heater experiment conducted by the Center for Nuclear Waste Regulatory Analyses. This experiment involves a fractured-porous rock system, composed of concrete slabs, heated by an electric heater placed in a 0.15 m diameter ''drift''. A substantial volume of water was released above the boiling zone over a time period of 135 days, giving rise to vaporization around the heat source. In this study, two basic conceptual models, similar to the thermal seepage models used in the Yucca Mountain Project, a dual-permeability model and an active-fracture model, are set up to predict evolution of temperature and saturation at the ''drift'' crown, and thereby to estimate potential for thermal seepage. Preliminary results from the model show good agreement with temperature profiles as well as with the potential seepage indicated in the lab experiments. These results build confidence in the thermal seepage models used in the Yucca Mountain Project. Different approaches are considered in our conceptual model to implement fracture-matrix interaction. Sensitivity analyses of fracture properties are conducted to help evaluation of uncertainty.
Date: July 30, 2004
Creator: Zhang, Y. & Birkholzer, J.
Partner: UNT Libraries Government Documents Department

DECOVALEX-THMC Task D: Long-Term Permeability/Porosity Changes inthe EDZ and Near Field due to THM and THC Processes in Volcanic andCrystaline-Bentonite Systems, Status Report October 2005

Description: The DECOVALEX project is an international cooperativeproject initiated by SKI, the Swedish Nuclear Power Inspectorate, withparticipation of about 10 international organizations. The name DECOVALEXstands for DEvelopment of COupled models and their VALidation againstExperiments. The general goal of this project is to encouragemultidisciplinary interactive and cooperative research on modelingcoupled processes in geologic formations in support of the performanceassessment for underground storage of radioactive waste. Three multi-yearproject stages of DECOVALEX have been completed in the past decade,mainly focusing on coupled thermal-hydrological-mechanicalprocesses.Currently, a fourth three-year project stage of DECOVALEX isunder way, referred to as DECOVALEX-THMC. THMC stands for Thermal,Hydrological, Mechanical, and Chemical processes. The new project stageaims at expanding the traditional geomechanical scope of the previousDECOVALEX project stages by incorporating geochemical processes importantfor repository performance. The U.S. Department of Energy (DOE) leadsTask D of the new DECOVALEX phase, entitled "Long-termPermeability/Porosity Changes in the EDZ and Near Field due to THC andTHM Processes for Volcanic and Crystalline-Bentonite Systems." In itsleadership role for Task D, DOE coordinates and sets the direction forthe cooperative research activities of the international research teamsengaged in Task D.
Date: November 1, 2005
Creator: Birkholzer, J.; Rutqvist, J.; Sonnenthal, E. & Barr, D.
Partner: UNT Libraries Government Documents Department

Coupled reservoir-geomechanical analysis of the potential fortensile and shear failure associated with CO2 injection in multilayeredreservoir-caprock systems

Description: Coupled reservoir-geomechanical simulations were conductedto study the potential for tensile and shear failure e.g., tensilefracturing and shear slip along pre-existing fractures associated withunderground CO2 injection in a multilayered geological system. Thisfailure analysis aimed to study factors affecting the potential forbreaching a geological CO2 storage system and to study methods forestimating the maximum CO2 injection pressure that could be sustainedwithout causing such a breach. We pay special attention to geomechanicalstress changes resulting from upward migration of the CO2 and how theinitial stress regime affects the potential for inducing failure. Weconclude that it is essential to have an accurate estimate of thethree-dimensional in situ stress field to support the design andperformance assessment of a geological CO2 injection operation. Moreover,we also conclude that it is important to consider mechanical stresschanges that might occur outside the region of increased reservoir fluidpressure (e.g., in the overburden rock) between the CO2-injectionreservoir and the ground surface.
Date: March 27, 2007
Creator: Rutqvist, J.; Birkholzer, J.T. & Tsang, C.-F.
Partner: UNT Libraries Government Documents Department

A method for quick assessment of CO2 storage capacity in closedand semi-closed saline formations

Description: Saline aquifers of high permeability bounded by overlying/underlying seals may be surrounded laterally by low-permeability zones, possibly caused by natural heterogeneity and/or faulting. Carbon dioxide (CO{sub 2}) injection into and storage in such 'closed' systems with impervious seals, or 'semi-closed' systems with nonideal (low-permeability) seals, is different from that in 'open' systems, from which the displaced brine can easily escape laterally. In closed or semi-closed systems, the pressure buildup caused by continuous industrial-scale CO{sub 2} injection may have a limiting effect on CO{sub 2} storage capacity, because geomechanical damage caused by overpressure needs to be avoided. In this research, a simple analytical method was developed for the quick assessment of the CO{sub 2} storage capacity in such closed and semi-closed systems. This quick-assessment method is based on the fact that native brine (of an equivalent volume) displaced by the cumulative injected CO{sub 2} occupies additional pore volume within the storage formation and the seals, provided by pore and brine compressibility in response to pressure buildup. With nonideal seals, brine may also leak through the seals into overlying/underlying formations. The quick-assessment method calculates these brine displacement contributions in response to an estimated average pressure buildup in the storage reservoir. The CO{sub 2} storage capacity and the transient domain-averaged pressure buildup estimated through the quick-assessment method were compared with the 'true' values obtained using detailed numerical simulations of CO{sub 2} and brine transport in a two-dimensional radial system. The good agreement indicates that the proposed method can produce reasonable approximations for storage-formation-seal systems of various geometric and hydrogeological properties.
Date: February 10, 2008
Creator: Zhou, Q.; Birkholzer, J.; Tsang, C.F. & Rutqvist, J.
Partner: UNT Libraries Government Documents Department

Numerical experiments on the probability of seepage intounderground openings in heterogeneous fractured rock

Description: An important issue for the performance of underground nuclear waste repositories is the rate of seepage into the waste emplacement drifts. A prediction of this rate is particularly complicated for the potential repository site at Yucca Mountain, Nevada, because it is located in thick, unsaturated, fractured tuff formations. Underground opening in unsaturated media might act as capillary barriers, diverting water around them. In the present work, they study the potential rate of seepage into drifts as a function of the percolation flux at Yucca Mountain, based on a stochastic model of the fractured rock mass in the drift vicinity. A variety of flow scenarios are considered, assuming present-day and possible future climate conditions. They show that the heterogeneity in the flow domain is a key factor controlling seepage rates, since it causes channelized flow and local ponding in the unsaturated flow field.
Date: April 15, 1998
Creator: Birkholzer, J.; Li, G.; Tsang, C.F. & Tsang, Y.
Partner: UNT Libraries Government Documents Department

The Effects of Unheated Sections on Mositure Transport in the Emplacement Drift

Description: A thermal-hydrologic natural-ventilation model is configured for simulating temperature, humidity, and condensate distributions in the coupled domains of the in-drift airspace and the near-field rockmass. Meaningful results are obtained from the model for a practical application in which the beneficial effects of unheated drift sections are analyzed. Sensitivity to the axial dispersion coefficient is also studied with the model.
Date: June 20, 2006
Creator: Danko, G.; Bahrami, D. & Birkholzer, J.T.
Partner: UNT Libraries Government Documents Department

Sensitivity study of CO2 storage capacity in brine aquifers withclosed boundaries: Dependence on hydrogeologic properties

Description: In large-scale geologic storage projects, the injected volumes of CO{sub 2} will displace huge volumes of native brine. If the designated storage formation is a closed system, e.g., a geologic unit that is compartmentalized by (almost) impermeable sealing units and/or sealing faults, the native brine cannot (easily) escape from the target reservoir. Thus the amount of supercritical CO{sub 2} that can be stored in such a system depends ultimately on how much pore space can be made available for the added fluid owing to the compressibility of the pore structure and the fluids. To evaluate storage capacity in such closed systems, we have conducted a modeling study simulating CO{sub 2} injection into idealized deep saline aquifers that have no (or limited) interaction with overlying, underlying, and/or adjacent units. Our focus is to evaluate the storage capacity of closed systems as a function of various reservoir parameters, hydraulic properties, compressibilities, depth, boundaries, etc. Accounting for multi-phase flow effects including dissolution of CO{sub 2} in numerical simulations, the goal is to develop simple analytical expressions that provide estimates for storage capacity and pressure buildup in such closed systems.
Date: February 7, 2007
Creator: Zhou, Q.; Birkholzer, J.; Rutqvist, J. & Tsang, C-F.
Partner: UNT Libraries Government Documents Department

Estimating maximum sustainable injection pressure duringgeological sequestration of CO2 using coupled fluid flow andgeomechanical fault-slip analysis

Description: This paper demonstrates the use of coupled fluid flow andgeomechanical fault slip (fault reactivation) analysis to estimate themaximum sustainable injection pressure during geological sequestration ofCO2. Two numerical modeling approaches for analyzing faultslip areapplied, one using continuum stress-strain analysis and the other usingdiscrete fault analysis. The results of these two approaches to numericalfault-slip analyses are compared to the results of a more conventionalanalytical fault-slip analysis that assumes simplified reservoirgeometry. It is shown that the simplified analytical fault-slip analysismay lead to either overestimation or underestimation of the maximumsustainable injection pressure because it cannot resolve importantgeometrical factors associated with the injection induced spatialevolution of fluid pressure and stress. We conclude that a fully couplednumerical analysis can more accurately account for the spatial evolutionof both insitu stresses and fluid pressure, and therefore results in amore accurate estimation of the maximum sustainable CO2 injectionpressure.
Date: October 17, 2006
Creator: Rutqvist, J.; Birkholzer, J.; Cappa, F. & Tsang, C.-F.
Partner: UNT Libraries Government Documents Department

Non-isothermal flow in low permeable porous media: A comparison of Richards' and two-phase flow approaches

Description: The present work compares the performance of two alternative flow models for the simulation of thermal-hydraulic coupled processes in low permeable porous media: non-isothermal Richards and two-phase flow concepts. Both models take vaporization processes into account: however, the Richards model neglects dynamic pressure variations and bulk flow of the gaseous phase. For the comparison of the two approaches first published data from a laboratory experiment is studied involving thermally driven moisture flow in a partially saturated bentonite sample. Then a benchmark test of longer-term thermal-hydraulic behavior in the engineered barrier system of a geological nuclear waste repository is analyzed (DECOVALEX project). It was found that both models can be used to reproduce the vaporization process if the intrinsic permeability is relative high. However, when a thermal-hydraulic coupled problem has the same low intrinsic permeability for both the liquid and the gas phase, only the two-phase flow approach provides reasonable results.
Date: March 15, 2010
Creator: Wang, W.; Rutqvist, J.; Gorke, U.-J.; Birkholzer, J.T. & Kolditz, O.
Partner: UNT Libraries Government Documents Department

Temperature, humidity and air flow in the emplacement drifts using convection and dispersion transport models

Description: A coupled thermal-hydrologic-airflow model is developed, solving for the transport processes within a waste emplacement drift and the surrounding rockmass together at the proposed nuclear waste repository at Yucca Mountain. Natural, convective air flow as well as heat and mass transport in a representative emplacement drift during post-closure are explicitly simulated, using the MULTIFLUX model. The conjugate, thermal-hydrologic transport processes in the rockmass are solved with the TOUGH2 porous-media simulator in a coupled way to the in-drift processes. The new simulation results show that large-eddy turbulent flow, as opposed to small-eddy flow, dominate the drift air space for at least 5000 years following waste emplacement. The size of the largest, longitudinal eddy is equal to half of the drift length, providing a strong axial heat and moisture transport mechanism from the hot to the cold drift sections. The in-drift results are compared to those from simplified models using a surrogate, dispersive model with an equivalent dispersion coefficient for heat and moisture transport. Results from the explicit, convective velocity simulation model provide higher axial heat and moisture fluxes than those estimated from the previously published, simpler, equivalent-dispersion models, in addition to showing differences in temperature, humidity and condensation rate distributions along the drift length. A new dispersive model is also formulated, giving a time- and location-variable function that runs generally about ten times higher in value than the highest dispersion coefficient currently used in the Yucca Mountain Project as an estimate for the equivalent dispersion coefficient in the emplacement drift. The new dispersion coefficient variation, back-calculated from the convective model, can adequately describe the heat and mass transport processes in the emplacement drift example.
Date: October 1, 2009
Creator: Danko, G.; Birkholzer, J.T.; Bahrami, D. & Halecky, N.
Partner: UNT Libraries Government Documents Department

On scale and magnitude of pressure build-up induced by large-scale geologic storage of CO2

Description: The scale and magnitude of pressure perturbation and brine migration induced by geologic carbon sequestration is discussed assuming a full-scale deployment scenario in which enough CO{sub 2} is captured and stored to make relevant contributions to global climate change mitigation. In this scenario, the volumetric rates and cumulative volumes of CO{sub 2} injection would be comparable to or higher than those related to existing deep-subsurface injection and extraction activities, such as oil production. Large-scale pressure build-up in response to the injection may limit the dynamic storage capacity of suitable formations, because over-pressurization may fracture the caprock, may drive CO{sub 2}/brine leakage through localized pathways, and may cause induced seismicity. On the other hand, laterally extensive sedimentary basins may be less affected by such limitations because (i) local pressure effects are moderated by pressure propagation and brine displacement into regions far away from the CO{sub 2} storage domain; and (ii) diffuse and/or localized brine migration into overlying and underlying formations allows for pressure bleed-off in the vertical direction. A quick analytical estimate of the extent of pressure build-up induced by industrial-scale CO{sub 2} storage projects is presented. Also discussed are pressure perturbation and attenuation effects simulated for two representative sedimentary basins in the USA: the laterally extensive Illinois Basin and the partially compartmentalized southern San Joaquin Basin in California. These studies show that the limiting effect of pressure build-up on dynamic storage capacity is not as significant as suggested by Ehlig-Economides and Economides, who considered closed systems without any attenuation effects.
Date: May 1, 2011
Creator: Zhou, Q. & Birkholzer, J. T.
Partner: UNT Libraries Government Documents Department

Natural convection in tunnels at Yucca Mountain and impact on drift seepage

Description: The decay heat from radioactive waste that is to be disposed in the once proposed geologic repository at Yucca Mountain (YM) will significantly influence the moisture conditions in the fractured rock near emplacement tunnels (drifts). Additionally, large-scale convective cells will form in the open-air drifts and will serve as an important mechanism for the transport of vaporized pore water from the fractured rock in the drift center to the drift end. Such convective processes would also impact drift seepage, as evaporation could reduce the build up of liquid water at the tunnel wall. Characterizing and understanding these liquid water and vapor transport processes is critical for evaluating the performance of the repository, in terms of water-induced canister corrosion and subsequent radionuclide containment. To study such processes, we previously developed and applied an enhanced version of TOUGH2 that solves for natural convection in the drift. We then used the results from this previous study as a time-dependent boundary condition in a high-resolution seepage model, allowing for a computationally efficient means for simulating these processes. The results from the seepage model show that cases with strong natural convection effects are expected to improve the performance of the repository, since smaller relative humidity values, with reduced local seepage, form a more desirable waste package environment.
Date: April 15, 2010
Creator: Halecky, N.; Birkholzer, J.T. & Peterson, P.
Partner: UNT Libraries Government Documents Department

Modeling Single Well Injection-Withdrawal (SWIW) Tests for Characterization of Complex Fracture-Matrix Systems

Description: The ability to reliably predict flow and transport in fractured porous rock is an essential condition for performance evaluation of geologic (underground) nuclear waste repositories. In this report, a suite of programs (TRIPOLY code) for calculating and analyzing flow and transport in two-dimensional fracture-matrix systems is used to model single-well injection-withdrawal (SWIW) tracer tests. The SWIW test, a tracer test using one well, is proposed as a useful means of collecting data for site characterization, as well as estimating parameters relevant to tracer diffusion and sorption. After some specific code adaptations, we numerically generated a complex fracture-matrix system for computation of steady-state flow and tracer advection and dispersion in the fracture network, along with solute exchange processes between the fractures and the porous matrix. We then conducted simulations for a hypothetical but workable SWIW test design and completed parameter sensitivity studies on three physical parameters of the rock matrix - namely porosity, diffusion coefficient, and retardation coefficient - in order to investigate their impact on the fracture-matrix solute exchange process. Hydraulic fracturing, or hydrofracking, is also modeled in this study, in two different ways: (1) by increasing the hydraulic aperture for flow in existing fractures and (2) by adding a new set of fractures to the field. The results of all these different tests are analyzed by studying the population of matrix blocks, the tracer spatial distribution, and the breakthrough curves (BTCs) obtained, while performing mass-balance checks and being careful to avoid some numerical mistakes that could occur. This study clearly demonstrates the importance of matrix effects in the solute transport process, with the sensitivity studies illustrating the increased importance of the matrix in providing a retardation mechanism for radionuclides as matrix porosity, diffusion coefficient, or retardation coefficient increase. Interestingly, model results before and after hydrofracking are insensitive to adding ...
Date: November 1, 2010
Creator: Cotte, F.P.; Doughty, C. & Birkholzer, J.
Partner: UNT Libraries Government Documents Department