Chin-fu Tsang - Profile on Academia.edu (original) (raw)
Papers by Chin-fu Tsang
Flow and solute transport through porous medium with strongly varying hydraulic conductivity are ... more Flow and solute transport through porous medium with strongly varying hydraulic conductivity are studied by numerical simulations. The heterogeneity of the porous medium is defined by Ï and λâ², which are, respectively, the standard deviation of natural log of permeability values and its correlation range λ divided by transport distance L. The development of flow channeling as a function of
Geophysical Monograph Series, 2013
Dynamic channeling of flow and transport in strongly .heterogeneous, saturated and unsaturated me... more Dynamic channeling of flow and transport in strongly .heterogeneous, saturated and unsaturated media is reviewed. Focusing or channeling of flow is dependent on both the permeability distribution and the pressure field. In the case of unsaturated media, it is also dependent on the degree of saturation. The emergence of flow channeling as a function of permeability variability (as measured by its standard deviation) and the spatial correlation range in three-dimensional porous systems is described. We also discuss the effects of channelized flow on two problems of practical interest for saturated and unsaturated heterogeneous media.
The emplacement of a nuclear waste repository in a fractured porous medium provides a heat source... more 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. This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley Laboratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department of Energy to the exclusion of others that may be suitable. ",..;.
Hydrogeology Journal
A complete background information such as porosity, permeability, aquifer thickness, hydraulic he... more A complete background information such as porosity, permeability, aquifer thickness, hydraulic head, geometry of cap-rocks, salinity are necessary for the successful planning of the field injection or for modeling the flow and transport of injected supercritical CO 2 in the target formation. In the MUSTANG project, two new wells at the vicinity of Heletz 18 (H-18) are being drilled and will be used for the study of the effects of CO 2 injection for geological storage. To determine the hydraulic conductivity structure of a reservoir layer of new wells, the Flowing Fluid electric conductivity (FFEC) method will be applied. In this method, the wellbore water is first replaced by DI water (or a constant salinity distinctly different from that of formation water). Then the well is shut in and an electric conductivity probe is used to scan the electrical conductivity of borehole fluid as a function of depth and time while pumping the wellbore water at constant rate. At depth locations where water enters the borehole, the logs display peaks. Analysis of the time evolution and skewness of these peaks allows estimation of the flow rate and salinity, and further, if two or more logs are taken at different well flow rates, the initial ambient pressure heads of each individual inflow/feed point can also be estimated. The depth resolution of the inflow locations is typically of order of well diameter. These data can be used to define the detailed transmissivity/permeability structure of the reservoir layer. In the present presentation, the FFEC method will be applied to the salinity data on the target layer from the Heletz site and model analysis results will be compared with those from core samples.
Abstract: The interaction between mechanical deformation and fluid flow in fractured rock gives r... more Abstract: The interaction between mechanical deformation and fluid flow in fractured rock gives rise to a host of coupled hydromechanical processes, which form the basis of a number of interesting research questions with practical implications. This paper will first discuss these processes in general, describing two numerical models that have been developed to analyse these processes. Then, four very different studies will be presented to illustrate the richness of this field. The first study has to do with borehole injection testing to determine fracture parameters and how hydro-mechanical effects will modify test results. The second study is on stress changes (caused by stress release) in rock near a tunnel during excavation, which cause significant changes in fluid press-ures in the region. The third study is on the relationship between mechanical effects and flow aniso-tropy and channelling in a rock block with a fracture network. The fourth study pertains to the hydromechanical...
Computers and Geotechnics
We present a discussion of the state-of-the-art on the use of discrete fracture networks (DFNs) f... more We present a discussion of the state-of-the-art on the use of discrete fracture networks (DFNs) for modelling geometrical characteristics, geomechanical evolution and hydromechanical (HM) behaviour of natural fracture networks in rock. The DFN models considered include those based on geological mapping, stochastic generation and geomechanical simulation. Different types of continuum, discontinuum and hybrid geomechanical models that integrate DFN information are summarised. Numerical studies aiming at investigating geomechanical effects on fluid flow in DFNs are reviewed. The paper finally provides recommendations for advancing the modelling of coupled HM processes in fractured rocks through more physically-based DFN generation and geomechanical simulation.
An intercomparison study between simulation codes for terrestrial sequestration of CO2 is propose... more An intercomparison study between simulation codes for terrestrial sequestration of CO2 is proposed. The objectives are, on the one hand, to focus and evaluate key processes through numerical simulation and, on the other, to explore the strengths of different codes and achieve acceptance of such codes for use in the development of geologic systems for CO2 disposal. This will be carried out through the study of a series of test problems by groups using their simulation codes. A progression from simple and uncoupled to increasingly complex and coupled problems is envisioned. The proposed study will attempt to involve interested technical groups worldwide, and will proceed through an iterative process of problem definition, solution comparison, discussion and refinement. The Internet will be used as a medium for communicating and organizing activities, and for a flexible exchange of information and documentation of results. In addition, it is planned to hold a series of workshops. The present write-up includes an initial set of eight proposed test problems and represents the first step in the process. Readers are encouraged to communicate with us at the email address above to indicate their interest and to provide suggestions and input.
Hydrogeology Journal, 2013
Ground Water, 2005
Hydrogeology is a field closely related to the needs of society. Many problems of current nationa... more Hydrogeology is a field closely related to the needs of society. Many problems of current national and local interest require predictions of hydrogeological system behavior, and, in a number of important cases, the period of prediction is tens to hundreds of thousands of years. It is argued that the demand for such long-term hydrogeological predictions casts a new light on the future needs of hydrogeological research. Key scientific issues are no longer concerned only with simple processes or narrowly focused modeling or testing methods, but also with assessment of prediction uncertainties and confidence, couplings among multiple physico-chemical processes occurring simultaneously at a site, and the interplay between site characterization and predictive modeling. These considerations also have significant implications for hydrogeological education. With this view, it is asserted that hydrogeological directions and education need to be reexamined and possibly refocused to address specific needs for long-term predictions.
Water Resources Research, 2015
Significant progress in hydrology, especially in subsurface flow and solute transport, has been m... more Significant progress in hydrology, especially in subsurface flow and solute transport, has been made over the last 35 years because of sustained interest in underground nuclear waste repositories. The present paper provides an overview of the key hydrologic issues involved, and to highlight advances in their understanding and treatment because of these efforts. The focus is not on the development of radioactive waste repositories and their safety assessment, but instead on the advances in hydrologic science that have emerged from such studies. Work and results associated with three rock types, which are being considered to host the repositories, are reviewed, with a different emphasis for each rock type. The first rock type is fractured crystalline rock, for which the discussion will be mainly on flow and transport in saturated fractured rock. The second rock type is unsaturated tuff, for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository. The third rock type is clay-rich formations, whose permeability is very low in an undisturbed state. In this case, the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances; i.e., on the relevant coupled thermo-hydromechanical processes. The extensive research results, especially those from multiyear large-scale underground research laboratory investigations, represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research.
![Research paper thumbnail of Reply [to “Comment on ‘Flow and tracer transport in a single fracture: A stochastic model and its relation to some field observations’ by L. Moreno et al.”]](https://attachments.academia-assets.com/75953321/thumbnails/1.jpg)
](Water Resources Research, 1991
We thank Goode and Shapiro [this issue] for their comments on the particle-tracking method [Moren... more We thank Goode and Shapiro [this issue] for their comments on the particle-tracking method [Moreno et al., 1988] (hereina/'ter MT) which we used to study solute transport in a single fracture. The method we used is in the context of a typical finite difference method discretization scheme, and Goode and Shapiro are quite correct to point out that in our
Heat storage in aquifers: buoyancy flow and thermal-stratification problems
Heat Storage in aquifers involves injecting warm water into a confined aquifer and recovering the... more Heat Storage in aquifers involves injecting warm water into a confined aquifer and recovering the heat later by pumping out the warm water. Heat loss in the aquifers is roughly proportional to the area of the warm storage region which may be increased to unacceptable levels by buoyancy effects. Thermohydraulic problems in heat storage aquifers, methods for predicting the buoyancy
Engineering Geology
This paper studies the role of pre-existing fractures in the damage evolution around tunnel excav... more This paper studies the role of pre-existing fractures in the damage evolution around tunnel excavation in fractured rocks. The length distribution of natural fractures can be described by a power law model, whose exponent a defines the relative proportion of large and small fractures in the system. The larger a is, the higher proportion of small fractures is. A series of two-dimensional discrete fracture networks (DFNs) associated with different length exponent a and fracture intensity P 21 is generated to represent various scenarios of distributed preexisting fractures in the rock. The geomechanical behaviour of the fractured rock embedded with DFN geometry in response to isotropic/anisotropic in-situ stress conditions and excavation-induced perturbations is simulated using the hybrid finite-discrete element method (FEMDEM), which can capture the deformation of intact rocks, the interaction of matrix blocks, the displacement of natural fractures, and the propagation of new cracks. An excavation damaged zone (EDZ) develops around the man-made opening as a result of reactivation of preexisting fractures and propagation of wing cracks. The simulation results show that when a is small, the system which is dominated by large fractures can remain stable after excavation given that P 21 is not very high; however, intensive structurally-governed kinematic instability can occur if P 21 is sufficiently high and the fracture spacing is much smaller than the tunnel size. With the increase of a, the system becomes more dominated by small fractures, and the EDZ is mainly created by the coalescence of small fractures near the tunnel boundary. The results of this study have important implications for designing stable underground openings for radioactive waste repositories as well as other engineering facilities that are intended to generate minimal damage in the host rock mass.
Hydrogeology Journal
Access to the published version may require subscription. N.B. When citing this work, cite the or... more Access to the published version may require subscription. N.B. When citing this work, cite the original published paper.
Hydrologic testing during drilling: application of the flowing fluid electrical conductivity (FFEC) logging method to drilling of a deep borehole
Hydrogeology Journal
Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling pe... more Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling period. It is only done when drilling experiences a large loss (or high return) of drilling fluid due to penetration of a large-transmissivity zone. The paper proposes the possibility of conducting flowing fluid electric conductivity (FFEC) logging during the drilling period, with negligible impact on the drilling schedule, yet providing important information on depth locations of both high- and low-transmissivity zones and their hydraulic properties. The information can be used to guide downhole fluid sampling and post-drilling detailed testing of the borehole. The method has been applied to the drilling of a 2500-m borehole at Åre, central Sweden, firstly when the drilling reached 1600 m, and then when the drilling reached the target depth of 2500 m. Results unveil eight hydraulically active zones from 300 m down to borehole bottom, with depths determined to within the order of a meter. Further, the first set of data allows the estimation of hydraulic transmissivity values of the six hydraulically conductive zones found from 300 to 1600 m, which are very low and range over one order of magnitude.
Validation of mathematical models against experiments for radioactive waste repositories — DECOVALEX experience
Coupled Thermo-Hydro-Mechanical Processes of Fractured Media - Mathematical and Experimental Studies
ABSTRACT The international co-operative research project— DECOVALEX- is presented. The project wa... more ABSTRACT The international co-operative research project— DECOVALEX- is presented. The project was initiated as a collective research effort to further our understanding of the coupled thermo-hydro-mechanical processes in fractured media and engineered buffer materials, and validate mathematical models and computer codes against experiments for radioactive waste isolation. The presentation summarizes the organization, structure, approaches and management of the project briefly, followed by an outline of the Bench-Mark-Test (BMT) and Test Case (TC) problems studied in the project. The scientific achievements and lessons learned are briefly discussed at the end.
Numerical modeling of cyclic storage of hot water in aquifers
The LBL numerical model used is called CCC which stands for Conduction, Convection, and Compactio... more The LBL numerical model used is called CCC which stands for Conduction, Convection, and Compaction. The model computes heat and mass flow in three-dimensional water saturated porous systems. Concurrent with the mass and energy flow, the vertical deformation of the geothermal system is simulated using the one-dimensional consolidation theory of Terzaghi. Thus the following physical effects can be included simultaneously
Analytic study of geothermal reservoir pressure response to cold water reinjection
International Journal of Greenhouse Gas Control, 2015
The interaction between mechanical deformation and fluid flow in fault zones gives rise to a host... more The interaction between mechanical deformation and fluid flow in fault zones gives rise to a host of coupled hydro-mechanical processes fundamental to fault instability, induced seismicity, and associated fluid migration. Fault stability is studied in the context of the Heletz site which was chosen as a test site for CO 2 injection experiment in the framework of the EU-MUSTANG project. The potential reservoir for CO 2 storage at the Heletz site consists of three sandstone layers that are approximately one, two and nine meters in thickness, separated by impermeable shale layers of various thicknesses, and overlaid by a five-meter limestone and a thick impermeable shale, which serves as caprock. The storage formation is intersected by two pre-existing subvertical normal faults (F1 and F2) on two opposite sides of the injection point. A hydro-mechanical model was developed to study the interaction between mechanical deformation and fluid flow in the two faults during CO 2 injection and storage. We evaluate the consequences caused by potential fault reactivation, namely, the fault slip and the CO 2 leakage through the caprock. The difference in the results obtained by considering the three-layer storage formation as an equivalent single-layer storage formation is analysed. It was found that for the two cases the pore pressure evolution is similar, but the differences in the evolution of CO 2 saturation are significant, which is attributed to the differences in CO 2 spread in a single and three-layer storage. No fault reactivation was observed in either case. A sensitivity analysis was made to study the influence of the fault dip angle, the ratio between the horizontal and vertical stresses, the offset of the layers across fault F2, the initial permeability of the fault and the permeability of the confinement formations. Results show that reactivation of faults F1 and F2 is most sensitive to the stress ratio, the initial permeability of the faults and the permeability of the confinement formations. The offset of the layers across the fault F2 was also found to be an important parameter, mainly because an offset leads to an increase in CO 2 leakage. Changes in permeability were found to be small because plastic shear strains induced by the reactivation of the faults and associated increase in volumetric strains and permeability, occur mainly in a fault section of only 10 m length, which is the approximate total thickness of the storage layers.
Flow and solute transport through porous medium with strongly varying hydraulic conductivity are ... more Flow and solute transport through porous medium with strongly varying hydraulic conductivity are studied by numerical simulations. The heterogeneity of the porous medium is defined by Ï and λâ², which are, respectively, the standard deviation of natural log of permeability values and its correlation range λ divided by transport distance L. The development of flow channeling as a function of
Geophysical Monograph Series, 2013
Dynamic channeling of flow and transport in strongly .heterogeneous, saturated and unsaturated me... more Dynamic channeling of flow and transport in strongly .heterogeneous, saturated and unsaturated media is reviewed. Focusing or channeling of flow is dependent on both the permeability distribution and the pressure field. In the case of unsaturated media, it is also dependent on the degree of saturation. The emergence of flow channeling as a function of permeability variability (as measured by its standard deviation) and the spatial correlation range in three-dimensional porous systems is described. We also discuss the effects of channelized flow on two problems of practical interest for saturated and unsaturated heterogeneous media.
The emplacement of a nuclear waste repository in a fractured porous medium provides a heat source... more 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. This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley Laboratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department of Energy to the exclusion of others that may be suitable. ",..;.
Hydrogeology Journal
A complete background information such as porosity, permeability, aquifer thickness, hydraulic he... more A complete background information such as porosity, permeability, aquifer thickness, hydraulic head, geometry of cap-rocks, salinity are necessary for the successful planning of the field injection or for modeling the flow and transport of injected supercritical CO 2 in the target formation. In the MUSTANG project, two new wells at the vicinity of Heletz 18 (H-18) are being drilled and will be used for the study of the effects of CO 2 injection for geological storage. To determine the hydraulic conductivity structure of a reservoir layer of new wells, the Flowing Fluid electric conductivity (FFEC) method will be applied. In this method, the wellbore water is first replaced by DI water (or a constant salinity distinctly different from that of formation water). Then the well is shut in and an electric conductivity probe is used to scan the electrical conductivity of borehole fluid as a function of depth and time while pumping the wellbore water at constant rate. At depth locations where water enters the borehole, the logs display peaks. Analysis of the time evolution and skewness of these peaks allows estimation of the flow rate and salinity, and further, if two or more logs are taken at different well flow rates, the initial ambient pressure heads of each individual inflow/feed point can also be estimated. The depth resolution of the inflow locations is typically of order of well diameter. These data can be used to define the detailed transmissivity/permeability structure of the reservoir layer. In the present presentation, the FFEC method will be applied to the salinity data on the target layer from the Heletz site and model analysis results will be compared with those from core samples.
Abstract: The interaction between mechanical deformation and fluid flow in fractured rock gives r... more Abstract: The interaction between mechanical deformation and fluid flow in fractured rock gives rise to a host of coupled hydromechanical processes, which form the basis of a number of interesting research questions with practical implications. This paper will first discuss these processes in general, describing two numerical models that have been developed to analyse these processes. Then, four very different studies will be presented to illustrate the richness of this field. The first study has to do with borehole injection testing to determine fracture parameters and how hydro-mechanical effects will modify test results. The second study is on stress changes (caused by stress release) in rock near a tunnel during excavation, which cause significant changes in fluid press-ures in the region. The third study is on the relationship between mechanical effects and flow aniso-tropy and channelling in a rock block with a fracture network. The fourth study pertains to the hydromechanical...
Computers and Geotechnics
We present a discussion of the state-of-the-art on the use of discrete fracture networks (DFNs) f... more We present a discussion of the state-of-the-art on the use of discrete fracture networks (DFNs) for modelling geometrical characteristics, geomechanical evolution and hydromechanical (HM) behaviour of natural fracture networks in rock. The DFN models considered include those based on geological mapping, stochastic generation and geomechanical simulation. Different types of continuum, discontinuum and hybrid geomechanical models that integrate DFN information are summarised. Numerical studies aiming at investigating geomechanical effects on fluid flow in DFNs are reviewed. The paper finally provides recommendations for advancing the modelling of coupled HM processes in fractured rocks through more physically-based DFN generation and geomechanical simulation.
An intercomparison study between simulation codes for terrestrial sequestration of CO2 is propose... more An intercomparison study between simulation codes for terrestrial sequestration of CO2 is proposed. The objectives are, on the one hand, to focus and evaluate key processes through numerical simulation and, on the other, to explore the strengths of different codes and achieve acceptance of such codes for use in the development of geologic systems for CO2 disposal. This will be carried out through the study of a series of test problems by groups using their simulation codes. A progression from simple and uncoupled to increasingly complex and coupled problems is envisioned. The proposed study will attempt to involve interested technical groups worldwide, and will proceed through an iterative process of problem definition, solution comparison, discussion and refinement. The Internet will be used as a medium for communicating and organizing activities, and for a flexible exchange of information and documentation of results. In addition, it is planned to hold a series of workshops. The present write-up includes an initial set of eight proposed test problems and represents the first step in the process. Readers are encouraged to communicate with us at the email address above to indicate their interest and to provide suggestions and input.
Hydrogeology Journal, 2013
Ground Water, 2005
Hydrogeology is a field closely related to the needs of society. Many problems of current nationa... more Hydrogeology is a field closely related to the needs of society. Many problems of current national and local interest require predictions of hydrogeological system behavior, and, in a number of important cases, the period of prediction is tens to hundreds of thousands of years. It is argued that the demand for such long-term hydrogeological predictions casts a new light on the future needs of hydrogeological research. Key scientific issues are no longer concerned only with simple processes or narrowly focused modeling or testing methods, but also with assessment of prediction uncertainties and confidence, couplings among multiple physico-chemical processes occurring simultaneously at a site, and the interplay between site characterization and predictive modeling. These considerations also have significant implications for hydrogeological education. With this view, it is asserted that hydrogeological directions and education need to be reexamined and possibly refocused to address specific needs for long-term predictions.
Water Resources Research, 2015
Significant progress in hydrology, especially in subsurface flow and solute transport, has been m... more Significant progress in hydrology, especially in subsurface flow and solute transport, has been made over the last 35 years because of sustained interest in underground nuclear waste repositories. The present paper provides an overview of the key hydrologic issues involved, and to highlight advances in their understanding and treatment because of these efforts. The focus is not on the development of radioactive waste repositories and their safety assessment, but instead on the advances in hydrologic science that have emerged from such studies. Work and results associated with three rock types, which are being considered to host the repositories, are reviewed, with a different emphasis for each rock type. The first rock type is fractured crystalline rock, for which the discussion will be mainly on flow and transport in saturated fractured rock. The second rock type is unsaturated tuff, for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository. The third rock type is clay-rich formations, whose permeability is very low in an undisturbed state. In this case, the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances; i.e., on the relevant coupled thermo-hydromechanical processes. The extensive research results, especially those from multiyear large-scale underground research laboratory investigations, represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research.
Water Resources Research, 1991
We thank Goode and Shapiro [this issue] for their comments on the particle-tracking method [Moren... more We thank Goode and Shapiro [this issue] for their comments on the particle-tracking method [Moreno et al., 1988] (hereina/'ter MT) which we used to study solute transport in a single fracture. The method we used is in the context of a typical finite difference method discretization scheme, and Goode and Shapiro are quite correct to point out that in our
Heat storage in aquifers: buoyancy flow and thermal-stratification problems
Heat Storage in aquifers involves injecting warm water into a confined aquifer and recovering the... more Heat Storage in aquifers involves injecting warm water into a confined aquifer and recovering the heat later by pumping out the warm water. Heat loss in the aquifers is roughly proportional to the area of the warm storage region which may be increased to unacceptable levels by buoyancy effects. Thermohydraulic problems in heat storage aquifers, methods for predicting the buoyancy
Engineering Geology
This paper studies the role of pre-existing fractures in the damage evolution around tunnel excav... more This paper studies the role of pre-existing fractures in the damage evolution around tunnel excavation in fractured rocks. The length distribution of natural fractures can be described by a power law model, whose exponent a defines the relative proportion of large and small fractures in the system. The larger a is, the higher proportion of small fractures is. A series of two-dimensional discrete fracture networks (DFNs) associated with different length exponent a and fracture intensity P 21 is generated to represent various scenarios of distributed preexisting fractures in the rock. The geomechanical behaviour of the fractured rock embedded with DFN geometry in response to isotropic/anisotropic in-situ stress conditions and excavation-induced perturbations is simulated using the hybrid finite-discrete element method (FEMDEM), which can capture the deformation of intact rocks, the interaction of matrix blocks, the displacement of natural fractures, and the propagation of new cracks. An excavation damaged zone (EDZ) develops around the man-made opening as a result of reactivation of preexisting fractures and propagation of wing cracks. The simulation results show that when a is small, the system which is dominated by large fractures can remain stable after excavation given that P 21 is not very high; however, intensive structurally-governed kinematic instability can occur if P 21 is sufficiently high and the fracture spacing is much smaller than the tunnel size. With the increase of a, the system becomes more dominated by small fractures, and the EDZ is mainly created by the coalescence of small fractures near the tunnel boundary. The results of this study have important implications for designing stable underground openings for radioactive waste repositories as well as other engineering facilities that are intended to generate minimal damage in the host rock mass.
Hydrogeology Journal
Access to the published version may require subscription. N.B. When citing this work, cite the or... more Access to the published version may require subscription. N.B. When citing this work, cite the original published paper.
Hydrologic testing during drilling: application of the flowing fluid electrical conductivity (FFEC) logging method to drilling of a deep borehole
Hydrogeology Journal
Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling pe... more Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling period. It is only done when drilling experiences a large loss (or high return) of drilling fluid due to penetration of a large-transmissivity zone. The paper proposes the possibility of conducting flowing fluid electric conductivity (FFEC) logging during the drilling period, with negligible impact on the drilling schedule, yet providing important information on depth locations of both high- and low-transmissivity zones and their hydraulic properties. The information can be used to guide downhole fluid sampling and post-drilling detailed testing of the borehole. The method has been applied to the drilling of a 2500-m borehole at Åre, central Sweden, firstly when the drilling reached 1600 m, and then when the drilling reached the target depth of 2500 m. Results unveil eight hydraulically active zones from 300 m down to borehole bottom, with depths determined to within the order of a meter. Further, the first set of data allows the estimation of hydraulic transmissivity values of the six hydraulically conductive zones found from 300 to 1600 m, which are very low and range over one order of magnitude.
Validation of mathematical models against experiments for radioactive waste repositories — DECOVALEX experience
Coupled Thermo-Hydro-Mechanical Processes of Fractured Media - Mathematical and Experimental Studies
ABSTRACT The international co-operative research project— DECOVALEX- is presented. The project wa... more ABSTRACT The international co-operative research project— DECOVALEX- is presented. The project was initiated as a collective research effort to further our understanding of the coupled thermo-hydro-mechanical processes in fractured media and engineered buffer materials, and validate mathematical models and computer codes against experiments for radioactive waste isolation. The presentation summarizes the organization, structure, approaches and management of the project briefly, followed by an outline of the Bench-Mark-Test (BMT) and Test Case (TC) problems studied in the project. The scientific achievements and lessons learned are briefly discussed at the end.
Numerical modeling of cyclic storage of hot water in aquifers
The LBL numerical model used is called CCC which stands for Conduction, Convection, and Compactio... more The LBL numerical model used is called CCC which stands for Conduction, Convection, and Compaction. The model computes heat and mass flow in three-dimensional water saturated porous systems. Concurrent with the mass and energy flow, the vertical deformation of the geothermal system is simulated using the one-dimensional consolidation theory of Terzaghi. Thus the following physical effects can be included simultaneously
Analytic study of geothermal reservoir pressure response to cold water reinjection
International Journal of Greenhouse Gas Control, 2015
The interaction between mechanical deformation and fluid flow in fault zones gives rise to a host... more The interaction between mechanical deformation and fluid flow in fault zones gives rise to a host of coupled hydro-mechanical processes fundamental to fault instability, induced seismicity, and associated fluid migration. Fault stability is studied in the context of the Heletz site which was chosen as a test site for CO 2 injection experiment in the framework of the EU-MUSTANG project. The potential reservoir for CO 2 storage at the Heletz site consists of three sandstone layers that are approximately one, two and nine meters in thickness, separated by impermeable shale layers of various thicknesses, and overlaid by a five-meter limestone and a thick impermeable shale, which serves as caprock. The storage formation is intersected by two pre-existing subvertical normal faults (F1 and F2) on two opposite sides of the injection point. A hydro-mechanical model was developed to study the interaction between mechanical deformation and fluid flow in the two faults during CO 2 injection and storage. We evaluate the consequences caused by potential fault reactivation, namely, the fault slip and the CO 2 leakage through the caprock. The difference in the results obtained by considering the three-layer storage formation as an equivalent single-layer storage formation is analysed. It was found that for the two cases the pore pressure evolution is similar, but the differences in the evolution of CO 2 saturation are significant, which is attributed to the differences in CO 2 spread in a single and three-layer storage. No fault reactivation was observed in either case. A sensitivity analysis was made to study the influence of the fault dip angle, the ratio between the horizontal and vertical stresses, the offset of the layers across fault F2, the initial permeability of the fault and the permeability of the confinement formations. Results show that reactivation of faults F1 and F2 is most sensitive to the stress ratio, the initial permeability of the faults and the permeability of the confinement formations. The offset of the layers across the fault F2 was also found to be an important parameter, mainly because an offset leads to an increase in CO 2 leakage. Changes in permeability were found to be small because plastic shear strains induced by the reactivation of the faults and associated increase in volumetric strains and permeability, occur mainly in a fault section of only 10 m length, which is the approximate total thickness of the storage layers.