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Reservoir Description and Dynamics
Influence of Temperature And Fluid Pressure On the Fracture Network Evolution Around Deposition Holes of a KBS-3V Repository Concept At Forsmark, Sweden
Backers, Tobias (Swedish Radiation Safety Authority) | Stephansson, Ove (geomecon GmbH) | Sonnerfelt, Lena (Swedish Radiation Safety Authority) | Lanaro, Flavio (Swedish Radiation Safety Authority)
Abstract: A numerical modelling campaign aiming at the simulation of the development of the distinct fracture network under different geomechanical boundary conditions in a repository for spent nuclear fuel at Forsmark, Sweden, was carried out. The models included the KBS-3V deposition concept with backfill of the tunnel, readjustment of water head, swelling of the bentonite buffer and a full sequence of heat generation and cooling phase of the canisters. A subsequent glaciation scenario regarded an increase in vertical load due to the ice sheet and an increase of fluid pressure due to a hydraulic connection from the surface of the ice cover. The numerical simulations were run for two different Distinct Fracture Network (DFN) models and two stress regimes (i.e. a low magnitude and a high magnitude stress field). From the simulations it results that the understanding of the stress field at Forsmark appears to be critical for the propagation of the fractures. The low magnitude stress field (Ask et al. 2007) enhances the propagation of existing fractures in the network. On the other hand, the high magnitude stress field (Martin 2007) tends to close the existing fractures and mobilise the frictional resistance of the fracture with less propagation of the fractures. The numerical results show that during the operation, closure and thermal phase of the repository no major DFN alterations are to be expected. However, an increase of water head seems to have the most pronounced impact on the DFN evolution. 1 PREFACE In preparation for the review of the license application for disposal of spent nuclear fuel by the Swedish Nuclear Fuel and Waste Management Company (SKB), the Swedish Radiation Safety Authority (SSM) is conducting studies to evaluate the performance of the multi-barrier principle on which the KBS-3 system is based.
- Water & Waste Management (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Power Industry > Utilities > Nuclear (0.89)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (0.93)
Optimization of Orientation of Machine Hall Cavern Vishnugad Pipalkoti Hydro Electric Project (444 MW): A Numerical Modeling Approach
Singh, D. V. (THDC India Limited Rishikesh (Uttrakhand)) | Vishnoi, R. K. (THDC India Limited Rishikesh (Uttrakhand)) | Singhal, Sandeep (THDC India Limited Rishikesh (Uttrakhand)) | Badoni, A. K. (THDC India Limited Rishikesh (Uttrakhand))
Abstract: Based on the discontinuity data available up to detail project report (DPR) stage, a kinematic analysis using program "Unwedge3" was performed earlier for determining shape and size of potential wedges in machine hall cavern of Vishnugad Pipalkoti Hydro Electric Project (VPHEP) and thus optimizing the orientation of ma-chine hall cavern. Keeping various aspects in view, orientation of the axis of machine hall cavern of VPHEP was kept as N 320°. Thereafter additional investigations were done by exploratory drilling & drifting and hydro fracture test etc. The data on dis-continuities was updated by detailed geological logging of the drift. The hydro frac-ture test also revealed orientation of major horizontal principal stress along N 320°. Based on the latest assessment of data on discontinuity orientation and stress re-gime, a fresh kinematic analysis using program "Unwedge3" has been performed again for optimization of orientation of machine hall cavern. The kinematic analysis revealed that orientation of machine hall of VPHEP may be kept as N 305° instead of 320°, however in this case the cavern axis shall no longer be along the major horizon-tal stress. Therefore, 3D stress analyses for machine hall cavern has been done using program "Examine3D 4.0". The results pertaining to displacements, stresses & strength factor in both the orientation cases of the cavern are compared to arrive at conclusion for optimum orientation of the cavern. This paper provides an insight to the various aspects considered for kinematic analysis & 3-D stress analysis performed for optimization of orientation of the ma-chine hall cavern. 1 INTRODUCTION Vishnugad Pipalkoti HEP with installed capacity of 444 MW is one of the major on-going Hydro Electric Projects envisaged to harness the huge potential of river Alaknanda in district Chamoli of Uttarakhand State of India.
- Geology > Rock Type > Sedimentary Rock (0.50)
- Geology > Geological Subdiscipline > Geomechanics (0.48)
- Well Completion > Hydraulic Fracturing (0.89)
- Data Science & Engineering Analytics > Information Management and Systems (0.65)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.30)
Abstract: This paper addresses the problem of obtaining the information to support rock mechanics modelling and rock engineering design. A large amount of relevant material exists worldwide on previous rock parameter determinations, modelling exercises, design work, and construction projects. However, the information learnt from these activities is not easily accessible and useable, i.e. there has been no attempt to develop a ‘corporate memory’ system for rock mechanics and rock engineering. A structure for such a system is outlined comprising tables of intact and rock mass properties, libraries of standard and case example modelling solutions, and libraries of design and construction case examples. The procedure for initial implementation of the memory system under the aegis of the ISRM is described. 1 INTRODUCTION When conducting rock mechanics modelling and incorporating the results into rock engineering design, it is clearly advantageous to use all the relevant techniques and information that are available. Currently, this is often not achieved because knowledge of the techniques and information is not readily available, i.e. there is no overall mechanism for recalling the relevant information. In other words, the modelling and design is not supported by a ‘memory system’. We will term this memory the ‘corporate memory’ or ‘organisational memory’ of the rock mechanics and rock engineering community. The thrust of this general description of the corporate memory requirement applies directly to rock mechanics modelling and rock engineering design and is the motiva-tion for the content of this paper. Those of us involved in rock mechanics use our memory extensively in the modelling and design process, from understanding the rock mechanics principles, to estimating typical rock properties from experience, to having expertise with computer programs, to knowledge of previous modelling exercises, to rock construction designs that have succeeded, and sometimes failed.
- Energy > Oil & Gas (0.46)
- Energy > Power Industry (0.46)
- Well Drilling > Wellbore Design > Rock properties (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
Abstract: During the last years the demand for high frequency storage of natural gas increased dramatically. The new operation modes for gas storage caverns in rock salt mass require a more detailed rock mechanical consideration of thermal induced stress-es in the vicinity of the caverns. This means that the change of gas temperatures dur-ing operation and the consequences of these temperature changes on the stressing of the salt rock mass cannot be neglected any more, i.e. thermo-mechanical coupled cal-culations are necessary. As rock salt has a time dependent material behavior stress redistributions in the rock salt mass take place even under constant internal pressure conditions. Therefore not only the phases with different pressure change rates but also the duration of phases with nearly constant internal pressure have an influence on the resulting state varia-bles. Within the paper on principle two different loading scenarios are taken into ac-count. The first scenario is a cyclic pressure change with different withdrawal and injection rates, the second scenario includes idle time periods under maximum pres-sure. The main differences are demonstrated and discussed with respect to recommen-dations for the rock mechanical design rock salt has a time dependent material behav-ior stress redistributions in the rock salt mass take place even under constant internal pressure conditions. 1 INTRODUCTION The seasonal storage of natural gas in salt caverns has been practiced since some dec-ades successfully. Nowadays new operation modes are aimed at, which are character-ized by high withdrawal rates and possibly more than one pressure cycle per year. The main differences between seasonal and cyclic storage operations have been pointed out by Staudtmeister & Zapf (2010). This is important because no gas flow doesn't mean that the state variables like cavern temperature and stresses in the rock mass remain un-changed during this period.
- Geology > Mineral > Halide > Halite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Abstract: Following geological and geomechanical investigations with laboratory and in-situ tests, as well as the selection of the seismic input based on past earthquake records, stability analyses of the Venaus powerhouse cavern in Italy have been per-formed with both static and dynamic modeling studies. 2D and 3D design analyses have been carried out in static conditions by account-ing for the excavation-construction sequence, including the simulation of the rein-forcement system installed. Close attention has been given to the analysis of the dis-turbed zone around the cavern as well as to the reinforcement system used to insure the cavern stability. Performance monitoring data of crown displacements have been taken into account for appropriate validation of the analyses performed. Performance analyses have also been carried out under seismic conditions and for selected design ground motions. The dynamic response of the surrounding rock mass and of the reinforcement system has been investigated. The results obtained are of interest in relation to future stability analyses to be performed for large underground caverns constructed in the past, based on seismic design analyses and input data de-rived from updated post earthquake records recently made available in Italy. 1 INTRODUCTION It is generally assumed that underground structures are much safer to earthquake loading compared to surface structures. However, the experience in recent earthquakes has shown that some large size caverns did undergo damages so that performance analyses of underground openings under dynamic loading are of relevance and that in earthquake prone regions these analyses might be as important as under static condi-tions, This paper considers some dynamic modeling studies performed on the Venaus powerhouse cavern recently built in northern Italy, near the city of Turin, which is characterized by a significant rock mechanics database as derived during design and construction (Barla et al. 2008).
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.90)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.67)
Abstract: For determining factor of safety (FOS) for rock slopes using numerical strength reduction technique with Hoek Brown parameters, two different approaches are generally used. Approach I (Global): Approximation of the non-linear failure envelope by a best-fit linearization and subsequent global c-φ -reduction by classical approach. Approach II (Local): Determination of local c and φ values according to the local stress state and subsequent local c-φ –reduction. Different numerical methods based on "Global" and "Local" approaches are tested for rock slopes with different configurations, in different rocks at their different physical conditions. Analysis for determining FOS using Limit Equilibrium Method with equivalent c-phi values of Hoek-Brown parameters (RocLab) was also carried out. As observed, global approach in comparison to the local approach can lead to a deviation of about ± 15 %, for rocks with GSI values up to 65. FOS values determined using Limit Equilibrium Method are mostly in higher (up to 10 %) side. If local approach is considered as more ‘correct’, depending on the parameters, results of the global approach can lie on the safe or unsafe site. Evaluation of slope stability using the global approach can result in uneconomic slope design or overestimation of safety margin. 1 INTRODUCTION For determination of safety factors, especially but not only for slopes, the numerical shear strength reduction technique, based on the Mohr-Coulomb constitutive law has became popular now a days, replacing the conventional limit equilibrium techniques. The Mohr-Coulomb constitutive law usually characterising the failure envelop for soils, is defined by a linear relation between shear- and normal stress and between minor and major principal stress, respectively. At present, some effort is being made for use of the classical shear strength reduc-tion approch based on the Mohr-Coulomb constitutive law towards the non-linear failure envelopes.
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics (0.95)
Abstract: During the construction process, of an underground excavation, the rockmass is damaged and beyond the damaged area the stresses are modified. These zones are collectively this is known as the excavation damages zones (EDZs). The lab results, including UCS and T as well as crack thresholds CI and CD can be used to determine numerical model input properties. With a large data set it is possible to test the best, mean, and worst case scenarios and to evaluate the results statistically. Using two rock data sets, a limestone and a granite, and two nominal stress re-gimes the influence of the best, mean and worst cases (with hi and lo outliers filtered) were computed to determine the sensitivity of EDZ dimensions. It was demonstrated that both an inner and outer excavation damage zone (EDZi and EDZo) could be dif-ferentiated using the model results by the reversal point in the volumetric strain (con-traction to extension). This indicates the transition between a confined micro-damaged state (EDZo) and a potentially dilated EDZi. The outer boundary of the highly dam-aged zone, HDZ, is related to volumetric strain and a reduction in minor stress con-finement. Guidelines are suggested for determining the EDZs around circular excava-tion models. Cumulative distributions for the dimensions of the EDZs were determined. The highly damaged zoned showed the least variability, were as the EDZo showed the most. This method can be used to determine the depth of a cutoff structure to limit the flow through the damage zone, for example, at the required confidence level. 1 INTRODUCTION The design of an underground excavation requires site specific data about the subsur-face. The level of complexity or the design life span will determine the volume of data necessary to adequately design the excavation.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (0.39)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.30)
- Well Drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (0.94)
Abstract: The presented study summarizes results from a numerical simulation campaign in the context of Task B in the DECOVALEX 2011. The project is based on the Äspö Pillar Stability experiment performed by the Swedish Nuclear Fuel and Waste Management Co at Äspö Hard Rock Laboratory. The experimental layout consists of two boreholes in an access tunnel leaving a pillar between them and heaters introduce thermal stresses in addition to the redistributed stresses from the excavations. The main focus was on the design, execution of, and observations during the experiment with particular attention to the yielding strength of the rock mass in the pillar. Based on the findings from the physical field experiments the rock response was simulated using FRACOD. FRACOD is a 2D boundary element software able to simulate the initiation, propagation and coalescence of fractures in geological media. Fracture initiation follows a Mohr-Coulomb criterion and fracture propagation is modeled by a fracture mechanics approach. The simulation campaign successfully back calculated the temperature evolution in the pillar during the heating phase, gave good predictions for the stress development, and gave very good agreement in simulated fracture patterns. The shallow spalling observed in the physical experiment as a result of the thermal heating was explicitly simulated using FRACOD. 1 INTRODUCTION The Swedish Nuclear Fuel and Waste Management Company SKB conducted the Äspö Pillar Stability Experiment (APSE) at the Äspö Hard Rock Laboratory. The major objective of the experiment was to determine the spalling/yielding strength of the granitic rock mass and to test how small confining pressures effect the yielding strength. To induce yielding a combination of excavation induced and thermally induced stresses were used in the experiment. The work described in this contribution was conducted within the context of the international DECOVALEX (2011) project.
- Water & Waste Management > Solid Waste Management (0.88)
- Energy > Power Industry > Utilities > Nuclear (0.70)
- Energy > Oil & Gas > Upstream (0.48)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics (1.00)
- Health, Safety, Environment & Sustainability > Environment > Waste management (0.69)
Abstract: The Prototype Repository at Äspö Hard Rock Laboratory is a large-scale experiment aimed at assessing the response of the rock mass and engineered barriers in a nuclear waste repository to changes in thermal, mechanical and hydraulic condi-tions. This paper describes the thermal and thermo-mechanical (TM) rock mechanics modelling conducted within the Prototype project so far. Comparison with measure-ments show that changes in temperature can be reproduced using homogeneous rock mass thermal properties. The TM models are used for spalling-potential assessment and for wedge stability analyses. Given the current material models and in situ stress models of the rock, spalling is concluded to be unlikely. Wedge stability predictions obtained using a semi-analytical approach, based on shear and normal stresses on hypothetical fracture planes in a linear elastic model, agree with results from models with explicitly modeled fractures. The rock mechanics evaluation of the outer section of the Prototype Repository is still in progress and there are not yet any systematic records of observations from the surfaces of the openings. With exception of the thermal assessment, all conclusions should be regarded as preliminary.When full access to the tunnel is possible, a complete comparison between modelling, measurements and observations will be made. 1 INTRODUCTION AND BACKGROUND The Swedish Nuclear Fuel and Waste Management Co.'s (SKB) Prototype Repository is a large-scale in situ experiment aimed at assessing the response of the rock mass and engineered barriers in a nuclear waste repository to changes in thermal, mecha-nical and hydraulic conditions. It is located at 450 m depth in the Äspö Hard Rock Laboratory and consists of a circular TBM tunnel and six full-scale vertical deposition holes drilled from the floor of the tunnel. These continuous data series are a valuable source of information for modelling purposes.
- North America > United States (0.46)
- Europe > Sweden (0.33)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
Long-Term Stability For a Proposed Nuclear Waste Deep Geological Repository: Bruce Nuclear Site, Ontario, Canada
Damjanac, Branko (Itasca Consulting Group, Inc) | Martin, Derek (University of Alberta) | Diederichs, Mark (Queens University) | McCreath, Dougal (Laurentian University) | Lam, Tom (Nuclear Waste Management Organization)
Abstract: Ontario Power Generation (OPG) is proposing a Deep Geologic Repository (DGR) for the long-term management of low and intermediate level radioactive waste generated at OPG owned or operated nuclear facilities. As envisioned, the DGR would be excavated within an 840 m thick, Paleozoic age, sedimentary sequence underlying the Bruce nuclear site in the Municipality of Kincardine, Ontario, Canada. Lateral development of the DGR would occur in the Cobourg Formation, an argilla-ceous limestone that is overlain by 200 m of Ordovician shale. As part of investi-gations conducted to assess the safety of the DGR, geomechanical analyses were carried out to evaluate rock-mass barrier integrity over a timeframe of 1Ma. The primary concern regarding long-term performance of the emplacement rooms is their degradation over time when subjected to different loading conditions, include-ing time-dependent strength degradation, seismicity, gas generation within the repo-sitory and multiple glacial loading/unloading cycles. This paper describes a series of analyses performed to explore rock mass stability and barrier integrity surrounding the waste emplacement rooms. Results indicate that while damage in the near field may arise over time, the capacity of the enclosing formation barrier to contain and isolate the waste is not affected. 1 INTRODUCTION Nuclear Waste Management Organization (NWMO), on behalf of Ontario Power Generation (OPG), is managing the development of a Deep Geologic Repository (DGR) for Low and Intermediate Level Waste (L&ILW) at the Bruce nuclear site, located in the municipality of Kincardine in Ontario, Canada. The site-specific, long-term geomechanical stability study was conducted as a part of the DGR site character-rization activities. The analy-ses included assessments of DGR cavern, pillar and shaft stability, and the evolution of damage and deformation of the surrounding rock mass in response to excavation activities and the long-term dynamic geological conditions expected at the site.
- North America > Canada > Ontario (1.00)
- North America > United States > Texas > Kleberg County (0.24)
- North America > United States > Texas > Chambers County (0.24)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.36)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.31)
- Water & Waste Management > Solid Waste Management (1.00)
- Government > Military (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (0.93)
- Health, Safety, Environment & Sustainability > Environment (0.89)