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Coupled processes in single fractures, double fractures and fractured porous media

Description: The emplacement of a nuclear waste repository in a fractured porous medium provides a heat source of large dimensions over an extended period of time. It also creates a large cavity in the rock mass, changing significantly the stress field. Such major changes induce various coupled thermohydraulic, hydromechanic and hydrochemical transport processes in the environment around a nuclear waste repository. The present paper gives, first, a general overview of the coupled processes involving thermal, mechanical, hydrological and chemical effects. Then investigations of a number of specific coupled processes are described in the context of fluid flow and transport in a single fracture, two intersecting fractures and a fractured porous medium near a nuclear waste repository. The results are presented and discussed.
Date: December 1, 1986
Creator: Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Mass transport in low permeability rocks under the influence of coupled thermomechanical and hydrochemical effects - an overview

Description: The present paper gives a general overview of mass transport in low permeability rocks under the coupled thermomechanical and hydrochemical effects associated with a nuclear waste repository. A classification of coupled processes is given. Then an ess is presented. example of a coupled process is presented. Discussions of coupled processes based on a recent LBL Panel meeting are summarized. 5 references, 3 figures, 4 tables.
Date: October 1, 1984
Creator: Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Aquifer thermal energy storage

Description: The concept of thermal energy storage in aquifers was suggested a few years ago. The idea is to store in aquifers large quantities of hot water produced (1) as a by-product of power plants, or (2) from solar energy collectors, and to retrieve the hot water for use when needed. Hence this method will, on the one hand, recover waste heat from power plants that is normally wasted, thus making possible the implementation of large-scale total energy systems. On the other hand, when used in conjunction with solar energy systems, aquifer energy storage provides a buffer between time-varying solar energy inputs and thermal or power demands. It is only recently that sophisticated computer models have been developed to study this storage system using the proper physical conditions and parameters, and to make realistic predictions of the energy storage and retrieval efficiencies. Furthermore, field experiments are currently underway to test this concept. Analytical and numerical studies at the Lawrence Berkeley Laboratory are described. The hydrodynamic and thermal behaviors of the storage system are analyzed and illustrated. The ratio of energy retrieval over energy stored is predicted to be as high as 80%.
Date: January 1, 1978
Creator: Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Theoretical studies in long-term thermal energy storage in aquifers

Description: One of the most promising methods for long-term thermal energy storage is the use of underground aquifers. LBL studies in this field are described. These theoretical studies were carried out in two directions: basic or generic studies to understand the fundamental thermohydrologic processes and to identify key parameters; and site-specific modeling studies to understand experimental observations and to simulate or predict field results. As a result of this work and similar work by other researchers, it is concluded that the phenomenology of the thermohydraulic flow associated with aquifer thermal energy storage is reasonably well understood, and that with the provision that an aquifer is properly selected and carefully characterized, an aquifier energy storage system can be successfully designed.
Date: November 1, 1980
Creator: Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Panel report on coupled thermo-mechanical-hydro-chemical processes associated with a nuclear waste repository

Description: Four basic physical processes, thermal, hydrological, mechanical and chemical, are likely to occur in 11 different types of coupling during the service life of an underground nuclear waste repository. A great number of coupled processes with various degrees of importance for geological repositories were identified and arranged into these 11 types. A qualitative description of these processes and a tentative evaluation of their significance and the degree of uncertainty in prediction is given. Suggestions for methods of investigation generally include, besides theoretical work, laboratory and large scale field testing. Great efforts of a multidisciplinary nature are needed to elucidate details of several coupled processes under different temperature conditions in different geological formations. It was suggested that by limiting the maximum temperature to 100{sup 0}C in the backfill and in the host rock during the whole service life of the repository the uncertainties in prediction of long-term repository behavior might be considerably reduced.
Date: July 1, 1984
Creator: Tsang, C. F. & Mangold, D. C.
Partner: UNT Libraries Government Documents Department

Preclosure monitoring and performance confirmation at Yucca Mountain: Applicability of geophysical, geohydrological, and geochemical methods

Description: The present paper presents considerations on studies that would be required for preclosure monitoring and performance confirmation of a nuclear waste geologic repository in an unsaturated zone. The critical parameters that should be monitored are reviewed and two scales of measurement relevant to monitoring activities, room scale and repository scale, are taken as a framework for investigation. A number of monitoring methods based on geophysics, geohydrology, and geochemistry are briefly summarized for their potential usefulness for preclosure monitoring and performance confirmation of the geologic repository. Particular emphasis is given to measurement of the spatial distribution of parameters in contrast to single-point measurements of quantities. 12 refs., 1 fig., 1 tab.
Date: June 1, 1989
Creator: Tsang, C.F.
Partner: UNT Libraries Government Documents Department

A broad view of model validation

Description: The safety assessment of a nuclear waste repository requires the use of models. Such models need to be validated to ensure, as much as possible, that they are a good representation of the actual processes occurring in the real system. In this paper we attempt to take a broad view by reviewing step by step the modeling process and bringing out the need to validating every step of this process. This model validation includes not only comparison of modeling results with data from selected experiments, but also evaluation of procedures for the construction of conceptual models and calculational models as well as methodologies for studying data and parameter correlation. The need for advancing basic scientific knowledge in related fields, for multiple assessment groups, and for presenting our modeling efforts in open literature to public scrutiny is also emphasized. 16 refs.
Date: October 1, 1989
Creator: Tsang, C.F.
Partner: UNT Libraries Government Documents Department

A code to compute borehole fluid conductivity profiles with multiple feed points

Description: Investigators wish to determine the flow characteristics of fractures intersecting a wellbore to understand the hydrologic behavior of fractured rocks. Often inflow from these fractures into the wellbore is at very low rates. A new procedure has been proposed and a corresponding method of analysis developed to obtain fracture inflow parameters from a time sequence of electric conductivity logs of the borehole fluid. The present report gives the details of equations and computer code used to compute borehole fluid conductivity distributions. Verification of the code used and a listing of the code are also given. 9 refs., 5 figs., 7 tabs.
Date: March 1, 1988
Creator: Hale, F.V. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Analytic study of geothermal reservoir pressure response to cold water reinjection

Description: Derivation of the governing equation, including temperature effects, is given where the permeability-viscosity ratio is assumed to be an arbitrary function of r{sup 2}t. This function is represented by a Fermi-Dirac function, whose parameters are determined based upon physical considerations. The solution for the pressure change is analytic except for the final step, where a numerical integration is called for. The results and implications of the calculations are discussed. Summary and concluding remarks are presented.
Date: November 1, 1978
Creator: Tsang, Y.W. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Injection into a fractured geothermal reservoir

Description: A detailed study is made on the movement of the thermal fronts in the fracture and in the porous medium when 100{sup 0}C water is injected into a 300{sup 0}C geothermal reservoir with equally spaced horizontal fractures. Numerical modeling calculations were made for a number of thermal conductivity values, as well as different values of the ratio of fracture and rock medium permeabilities. One important result is an indication that although initially, the thermal front in the fracture moves very fast relative to the front in the porous medium as commonly expected, its speed rapidly decreases. At some distance from the injection well the thermal fronts in the fracture and the porous medium coincide, and from that point they advance together. The implication of this result on the effects of fractures on reinjection into geothermal reservoirs is discussed.
Date: May 1, 1980
Creator: Bodvarsson, G.S. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Aquifer thermal energy storage: a survey

Description: The disparity between energy production and demand in many power plants has led to increased research on the long-term, large-scale storage of thermal energy in aquifers. Field experiments have been conducted in Switzerland, France, the United States, Japan, and the People's Republic of China to study various technical aspects of aquifer storage of both hot and cold water. Furthermore, feasibility studies now in progress include technical, economic, and environmental analyses, regional exploration to locate favorable storage sites, and evaluation and design of pilot plants. Several theoretical and modeling studies are also under way. Among the topics being studied using numerical models are fluid and heat flow, dispersion, land subsidence or uplift, the efficiency of different injection/withdrawal schemes, buoyancy tilting, numerical dispersion, the use of compensation wells to counter regional flow, steam injection, and storage in narrow glacial deposits of high permeability. Experiments to date illustrate the need for further research and development to ensure successful implementation of an aquifer storage system. Some of the areas identified for further research include shape and location of the hydrodynamic and thermal fronts, choice of appropriate aquifers, thermal dispersion, possibility of land subsidence or uplift, thermal pollution, water chemistry, wellbore plugging and heat exchange efficiency, and control of corrosion.
Date: January 1, 1980
Creator: Tsang, C.F.; Hopkins, D. & Hellstroem, G.
Partner: UNT Libraries Government Documents Department

Listing of scientific data on the Baca Geothermal Field

Description: This document is a record of the available open-file technical data collected at the Baca Geothermal Field, New Mexico. The data base is located at the Earth Sciences Division of the Lawrence Berkeley Laboratory, Berkeley, California. This document will serve as a handbook for using the data base. Section 1 includes general reference materials such as published reports, bibliographies, and proposals. Section 2 contains various types of progress reports. Sections 3 and 4 describe individual well data: Section 3 consists of well log data (retained in both the original and digitized forms) and Section 4 lists various tests carried out in the different wells. Data in both Sections are listed by test date.
Date: June 1, 1984
Creator: Spencer, R.K. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Buoyancy flow in fractures intersecting a nuclear waste repository

Description: The thermally induced buoyancy flow in fractured rocks around a nuclear waste repository is of major concern in the evaluation of the regional, long-term impact of nuclear waste disposal in geological formation. In this study, buoyancy flow and the development of convective cells are calculated in vertical fractures passing through or positioned near a repository. Interaction between buoyancy flow and regional hydraulic gradient is studied as a function of time, and the interference of intersecting fractures with each other is also discussed.
Date: July 1, 1980
Creator: Wang, J.S.Y. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Nuclear chemistry. Annual report, 1974

Description: The 1974 Nuclear Chemistry Annual Report contains information on research in the following areas: nuclear science (nuclear spectroscopy and radioactivity, nuclear reactions and scattering, nuclear theory); chemical and atomic physics (heavy ion-induced atomic reactions, atomic and molecular spectroscopy, photoelectron spectroscopy and hyperfine interactions); physical, inorganic, and analytical chemistry (x-ray crystallography, physical and inorganic chemistry, geochemistry); and instrumentation. Thesis abstracts, 1974 publication titles, and an author index are also included. Papers having a significant amount of information are listed separately by title. (RWR)
Date: July 1, 1975
Creator: Conzett, H.E.; Edelstein, N.M. & Tsang, C.F. (eds.)
Partner: UNT Libraries Government Documents Department

Reservoir Testing Using Simultaneous Measurements in More Than One Well

Description: The results of a preliminary study of transient well test analysis using simultaneous pressure measurements in two wells is reported. Using the simultaneous measurements from production-injection or production-production doublets results in a straight line plot of the ratio ({Delta}P{sub 1} – {Delta}P{sub 2})/(q{sub 1} – q{sub 2}) versus a function of time. The straight lines are the results of cancellation of terms when the contribution from the two wells are combined, as will be shown below. The use of simultaneous well test analysis can be used in conjunction with single well analysis methods to provide redundant estimates for the effective formation parameters, and for non-linear effects. 1 tab., 5 figs.
Date: December 1, 1976
Creator: Tsang, C.F. & Schroeder, R.C.
Partner: UNT Libraries Government Documents Department

Analysis of three sets of SWIW tracer-test data using a two-population complex fracture model for matrix diffusion and sorption

Description: A complex fracture model employing two populations for diffusion and sorption is proposed to analyze three representative single-well injection-withdrawal (SWIW) tracer tests from Forsmark and Laxemar, the two sites under investigation by the Swedish Nuclear Fuel and Waste Management Company (SKB). One population represents the semi-infinite rock matrix and the other represents finite blocks that can become saturated, thereafter accepting no further diffusion or sorption. The diffusion and sorption parameters of the models are inferred by matching tracer breakthrough curves (BTCs). Three tracers are simultaneously injected, uranine (Ur), which is conservative, and rubidium (Rb) and cesium (Cs), which are non-conservative. For non-sorbing tracer uranine, the finite blocks become saturated with test duration of the order of 10 hours, and both the finite and the semi-infinite populations play a distinct role in controlling BTCs. For sorbing tracers Rb and Cs, finite blocks do not saturate, but act essentially as semi-infinite, and thus BTC behavior is comparable to that obtained for a model containing only a semi-infinite rock matrix. The ability to obtain good matches to BTCs for both sorbing and non-sorbing tracers for these three different SWIW data sets demonstrates that the two-population complex fracture model may be a useful conceptual model to analyze all SWIW tracer tests in fractured rock, and perhaps also usual multiwell tracer tests. One of the two populations should be semi-infinite rock matrix and the other finite blocks that can saturate. The latter can represent either rock blocks or gouge within the fracture, a fracture skin zone, or stagnation zones.
Date: August 1, 2009
Creator: Doughty, C. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Critical parameters and measurement methods for post closure monitoring: A review of the state of the art and recommendations for further studies

Description: Both NRC and EPA regulations require programs of post closure monitoring to detect substantial and detrimental deviations from expected performance. The unexpected in this case would involve anomalous stress changes that might rupture the canisters or changes in the hydrologic regime that might accelerate corrosion. In the event of leakage brought about by any means transport of radionuclides to the accessible environment could occur through unexpected changes in the hydrologic flow regime caused either by the long term effects of the thermal loading by the waste or by changes in regional stress or hydrology. Studies of performance confirmation have identified six parameters or conditions that should be monitored that are associated with the thermal, mechanical and hydrologic phenomena introduced by the waste heat: temperature, stress, displacement, pore pressure, groundwater velocity and permeability. Since it is the thermal load that continues to increase after decommissioning, and which continues to alter the stress field and the hydrological regime, these same six parameters remain the critical ones in post closure monitoring. At two of the repository sites fractures have been clearly shown to be critical in modelling and performance confirmation; at the tuff site fluid saturation is also a critical parameter and for all the sites estimates of the groundwater velocity through the site are very important. Changes in fracture properties, saturation and fluid flow are thus of continuing importance in post closure monitoring. 14 refs., 19 figs.
Date: May 1, 1987
Creator: Morrison, H.F.; Majer, E.L. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Workshop on CSDP data needs for the BACA geothermal field: a summary

Description: These workshop summaries discuss the data needs of the Continental Scientific Drilling Program (CSDP) community and provide an introduction to the available geological, geophysical, geochemical and reservoir engineering data of the Baca geothermal field, Valles Caldera, New Mexico. Individual abstracts have been prepared for the presentations. (ACR)
Date: June 1, 1984
Creator: Mangold, D.C. & Tsang, C.F. (eds.)
Partner: UNT Libraries Government Documents Department

Advances in the study of far-field phenomena affecting repository performance

Description: Studies of far-field phenomena affecting repository performance have focussed on the role of fractures and other heterogeneities in the potential transport of radioactive solutes from the repository to the biosphere. The present paper summarizes two recent advances in the subject: the channeling model for the understanding and analysis tracer transport in variable-aperture fractures and the modeling of coupled thermo-hydro-mechanical processes in geologic formation around a repository. The paper concludes with remarks on the need for duality in the approach to performance assessment. One line of the duality is fundamental studies and the other, goal-oriented assessment to satisfy regulatory requirements. 15 refs., 10 figs., 1 tab.
Date: January 1, 1991
Creator: Tsang, C.F.
Partner: UNT Libraries Government Documents Department

Analysis of the response of geothermal reservoirs under injection and production procedures

Description: The response of a liquid-dominated geothermal reservoir to injection and production from a single well is studied. Different injection-production schemes are analyzed to explore how to minimize temporary cooling around the injection well and to optimize thermal recovery. The pressure response is also calculated, and found to be affected significantly by temperature-dependent viscosity variations. This will have implications on well-test methods for geothermal reservoirs. Vertical consolidation of the geothermal system during fluid withdrawal is also discussed, showing the need to establish previous stress history before attempting to predict the reservoir deformation. The transport of heat and fluid through a porous reservoir is computed using a numerical model. The one-dimensional consolidation theory of Terzaghi has been coupled to the heat and fluid flow to calculate reservoir compaction. No attempt is made of model chemical reactions or precipitation that might occur when waters of a different temperature and salinity are injected into the reservoir.
Date: April 1, 1977
Creator: Lippmann, M.J.; Tsang, C.F. & Witherspoon, P.A.
Partner: UNT Libraries Government Documents Department

Simulation of reinjection at Cerro Prieto using an idealized two-reservoir model

Description: An idealized two-reservoir model was introduced to explore some of the effects of reinjection in a geothermal field. For both the single-well model and the doublet model, the results indicate that reservoir pressures will be adequately maintained even when an intervening layer of low permeability is present. The same intervening layer may nevertheless be an effective barrier to the movement of cold fronts, due to the effect of gravity and viscosity on the flow of denser colder waters. This shows promise for developing reinjection strategies that can be tested on more detailed simulation models for specific sites such as th Cerro Prieto field.
Date: February 1, 1980
Creator: Tsang, C.F.; Mangold, D.C. & Lippmann, M.J.
Partner: UNT Libraries Government Documents Department

Theoretical temperature fields for the Stripa heater project. Vol. 1

Description: The report concerns thermal conduction calculations for the three in-situ heater experiments at Stripa which constitute part of the Swedish-American Cooperative Program on Radioactive Waste Storage in Mined Caverns. A semianalytic solution based on the Green's function method has been developed for an array of arbitrary time-dependent finite line heaters in a semi-infinite medium. This method as well as a three dimensional numerical model using IFD (Integrated Finite Difference) technique has been applied to model the field situations at Stripa. Comparison has demonstrated that the finite line source solution for the rock temperature is in excellent agreement with the numerical model solution as well as with a closed form finite cylinder source solution. It was found that maximum temperature rise in the rock within the two year experiment period will be 178/sup 0/C for the 3.6 kW full-scale heater experiment, 345/sup 0/C for the full-scale experiment with a 5 kW central heater and eight 0.72 kW peripheral heaters, and less than 200/sup 0/C for the time-scaled experiment. The ring of eight peripheral heaters in the second full-scale experiment will provide a nominally uniform temperature rise within its perimeter a few weeks after turn-on. The high temperature zone is localized throughout the duration of all three experiments. Nevertheless, the effect of different spacings on the thermal interaction between adjacent radioactive waste canisters will be demonstrated by the time-scaled experiment. Detailed results are presented in the form of tables, temperature profiles and contour plots. Predicted temperatures have been stored in an on-site computer for real-time comparison with field data. 56 figures, 7 tables.
Date: September 1, 1978
Creator: Chan, T.; Cook, N.G.W. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department