The study of the mechanical behaviour of a rock mass can be performed by considering as a discont... more The study of the mechanical behaviour of a rock mass can be performed by considering as a discontinuous medium composed by rock blocks isolated by rock discontinuities. The mechanical behaviour of the global system is due to the local movements of blocks subjected to a certain state of stress and ruled by the rock mass mechanical features. Mechanical features of the rock mass are determined by the mechanical and the geometrical features of the rock matrix and rock joints that can be directly measured by experimental tests and in situ surveys. Laboratory and in situ measurements can be affected by scale effects, and in situ surveys can be carried on only on exposed rock faces. Consequently the mechanical behaviour must be calibrated by the comparison with in situ measurements. In a discontinuous medium, the localisation of the measurement devices strongly influences the measurement results and consequently a deep knowledge of the rock mass structure is required. For this reason a deterministic reconstruction of the rock mass that takes the real joint localisation into account represents the best possibility to obtain numerical previsions comparable with the in situ measurements whilst, the more common practice to reconstruct the rock mass on a statistical basis, can determine local behaviour in disagreement with the monitored one. A comparison between a deterministic and probabilistic rock mass tessellation is described in the paper together with the consequent discontinuous models. Geometrical rock mass models is carried on by means of a specific code (RESOBLOK) whilst the mechanical rock mass behaviour is studied by a 3D code (3DEC). The paper reports an application to a rock mass excavated for the extraction of blocks utilised in the ornamental stone industry.
It has been demonstrated that CO2 migration along a well is one of the greatest risks of CO2 migr... more It has been demonstrated that CO2 migration along a well is one of the greatest risks of CO2 migration out of a storage reservoir, for two reasons: CO2 migration along the injection well to the geology, and CO2 migration from geology to a remote well). Indeed, such combinations of vertical and horizontal flows may lead in a longer term to the migration of both CO2 and its impurities towards a critical aquifer or to the surface level, which are 'altered' scenarios that are to be considered in a risk assessment frame
... 042 1 Improvement of hydro mechanical behavior knowledge of rock joint from laboratory tests ... more ... 042 1 Improvement of hydro mechanical behavior knowledge of rock joint from laboratory tests and in-situ experiments P. Lopez LA EGO ... except the preliminary one), a negative morphology is reproduce with a rubber that gives precise reproduction of the asperities (SILAS-TIC). ...
... A. Stietel a, A. Millard a, E Treille a, E. Vuillod b, A. Thoraval b, R. Ababou ca CEA/DMT/SE... more ... A. Stietel a, A. Millard a, E Treille a, E. Vuillod b, A. Thoraval b, R. Ababou ca CEA/DMT/SEMT, CEN Saclay, BP N~ 91191 Gif/Yvette Cedex FRANCE b INERIS, Ecole des Mines, Parc de Saurupt 54042 Nancy Cedex FRANCE c IMFT, All6e du Professeur Camille Soulas 31400 ...
A comparison between 2D UDEC numerical modeling and in-situ hydromechanical (HM) measurements is ... more A comparison between 2D UDEC numerical modeling and in-situ hydromechanical (HM) measurements is performed to better understand the coupling processes in a fractured media. Measurements come from the Coaraze site that is a natural 19000~m3 site where geometrical, hydraulical and mechanical parameters are known. Pressure and normal displacements on 10 single fractures inside the site and surface tilting are permanently measured. Repetitive hydraulic loadings are produced by the closure of a floodgate located on a spring of the site. A 100~kPa water pressure increase cause instantaneous elastic deformation of fractures and rock matrix. Those datas were used to evaluate a coupled hydromechanical numerical analysis at the single fracture and at the whole rock mass scales. At the single fracture scale, the high non-linear relationship between measured normal displacements and pressures is well explained with a variable normal joint stiffness model modified from Bandis law in order to take into account the joint environment. The more general deformation of the rock mass results from the complex heterogeneous stress-permeability behavior of the fracture network. High permeable fractures apertures change of a factor 2 in response to changing fluid pressure whereas there is a low change of low permeable fractures apertures. A 2D UDEC model of the entire rock mass that takes into account the heterogeneity of constant normal joints stiffnesses deduced from single fracture analysis and permeabilities measured in the field best fit experimental datas. Nevertheless, model results remain far from measurements (10 to 20% differences) mainly because fractures network geometry and permeabilities high heterogeneity need to be simplified to run the model. This analysis shows that it is possible to deduce hydromechanical non-linear laws from in-situ hydromechanical tests on single fractures with a good accuracy. Nevertheless, even with these laws taken as input parameters, it remains insufficient to restore a satisfying general behavior of a rock mass.
<p>As many industrial activities impacting the underground,... more <p>As many industrial activities impacting the underground, deep geothermal projects can be associated with the occurrence of induced seismic events. This seismicity is sometimes a direct consequence of stimulation operations needed to enhance the permeability of geothermal reservoirs, but, in other cases, it can also occur in different phases of geothermal projects, as during wells shut-in, after injection operations, or during the production phase, which generally implies lower flow rates and injection pressures. The intensity of this seismicity, in terms of magnitudes of seismic events, can be extremely variable, from microseismic events (M < 2), not felt at the surface, to large earthquakes (M > 5) that pose a serious risk to neighboring populations and may lead to the abandon of geothermal projects. In this context, it is of paramount importance to: i) better characterize and understand the interactions between natural and anthropogenic factors which may lead to geothermal-induced seismicity and ii) evaluate currently applied approaches to handle and minimize associated risks.</p><p>The objective of this work is to establish a state of the art about deep geothermal-induced seismicity, by describing factors that have a bearing on the generation of seismic events, as well as by discussing existing means to handle their occurrence. Based on a worldwide review of geothermal projects, we created a large database describing each selected case study in terms of geological properties and tectonic setting, operational parameters and type of geothermal systems, as well as spatio-temporal characteristics of the observed induced seismicity. Collected data are analyzed in order to better understand possible cause-effect relationships between induced seismicity and geothermal operations with the aim of identifying the most important preexisting and anthropogenic factors, as well as their interactions, which may have a key role on the occurrence of seismic activity.       </p>
The study of the mechanical behaviour of a rock mass can be performed by considering as a discont... more The study of the mechanical behaviour of a rock mass can be performed by considering as a discontinuous medium composed by rock blocks isolated by rock discontinuities. The mechanical behaviour of the global system is due to the local movements of blocks subjected to a certain state of stress and ruled by the rock mass mechanical features. Mechanical features of the rock mass are determined by the mechanical and the geometrical features of the rock matrix and rock joints that can be directly measured by experimental tests and in situ surveys. Laboratory and in situ measurements can be affected by scale effects, and in situ surveys can be carried on only on exposed rock faces. Consequently the mechanical behaviour must be calibrated by the comparison with in situ measurements. In a discontinuous medium, the localisation of the measurement devices strongly influences the measurement results and consequently a deep knowledge of the rock mass structure is required. For this reason a deterministic reconstruction of the rock mass that takes the real joint localisation into account represents the best possibility to obtain numerical previsions comparable with the in situ measurements whilst, the more common practice to reconstruct the rock mass on a statistical basis, can determine local behaviour in disagreement with the monitored one. A comparison between a deterministic and probabilistic rock mass tessellation is described in the paper together with the consequent discontinuous models. Geometrical rock mass models is carried on by means of a specific code (RESOBLOK) whilst the mechanical rock mass behaviour is studied by a 3D code (3DEC). The paper reports an application to a rock mass excavated for the extraction of blocks utilised in the ornamental stone industry.
It has been demonstrated that CO2 migration along a well is one of the greatest risks of CO2 migr... more It has been demonstrated that CO2 migration along a well is one of the greatest risks of CO2 migration out of a storage reservoir, for two reasons: CO2 migration along the injection well to the geology, and CO2 migration from geology to a remote well). Indeed, such combinations of vertical and horizontal flows may lead in a longer term to the migration of both CO2 and its impurities towards a critical aquifer or to the surface level, which are 'altered' scenarios that are to be considered in a risk assessment frame
... 042 1 Improvement of hydro mechanical behavior knowledge of rock joint from laboratory tests ... more ... 042 1 Improvement of hydro mechanical behavior knowledge of rock joint from laboratory tests and in-situ experiments P. Lopez LA EGO ... except the preliminary one), a negative morphology is reproduce with a rubber that gives precise reproduction of the asperities (SILAS-TIC). ...
... A. Stietel a, A. Millard a, E Treille a, E. Vuillod b, A. Thoraval b, R. Ababou ca CEA/DMT/SE... more ... A. Stietel a, A. Millard a, E Treille a, E. Vuillod b, A. Thoraval b, R. Ababou ca CEA/DMT/SEMT, CEN Saclay, BP N~ 91191 Gif/Yvette Cedex FRANCE b INERIS, Ecole des Mines, Parc de Saurupt 54042 Nancy Cedex FRANCE c IMFT, All6e du Professeur Camille Soulas 31400 ...
A comparison between 2D UDEC numerical modeling and in-situ hydromechanical (HM) measurements is ... more A comparison between 2D UDEC numerical modeling and in-situ hydromechanical (HM) measurements is performed to better understand the coupling processes in a fractured media. Measurements come from the Coaraze site that is a natural 19000~m3 site where geometrical, hydraulical and mechanical parameters are known. Pressure and normal displacements on 10 single fractures inside the site and surface tilting are permanently measured. Repetitive hydraulic loadings are produced by the closure of a floodgate located on a spring of the site. A 100~kPa water pressure increase cause instantaneous elastic deformation of fractures and rock matrix. Those datas were used to evaluate a coupled hydromechanical numerical analysis at the single fracture and at the whole rock mass scales. At the single fracture scale, the high non-linear relationship between measured normal displacements and pressures is well explained with a variable normal joint stiffness model modified from Bandis law in order to take into account the joint environment. The more general deformation of the rock mass results from the complex heterogeneous stress-permeability behavior of the fracture network. High permeable fractures apertures change of a factor 2 in response to changing fluid pressure whereas there is a low change of low permeable fractures apertures. A 2D UDEC model of the entire rock mass that takes into account the heterogeneity of constant normal joints stiffnesses deduced from single fracture analysis and permeabilities measured in the field best fit experimental datas. Nevertheless, model results remain far from measurements (10 to 20% differences) mainly because fractures network geometry and permeabilities high heterogeneity need to be simplified to run the model. This analysis shows that it is possible to deduce hydromechanical non-linear laws from in-situ hydromechanical tests on single fractures with a good accuracy. Nevertheless, even with these laws taken as input parameters, it remains insufficient to restore a satisfying general behavior of a rock mass.
<p>As many industrial activities impacting the underground,... more <p>As many industrial activities impacting the underground, deep geothermal projects can be associated with the occurrence of induced seismic events. This seismicity is sometimes a direct consequence of stimulation operations needed to enhance the permeability of geothermal reservoirs, but, in other cases, it can also occur in different phases of geothermal projects, as during wells shut-in, after injection operations, or during the production phase, which generally implies lower flow rates and injection pressures. The intensity of this seismicity, in terms of magnitudes of seismic events, can be extremely variable, from microseismic events (M < 2), not felt at the surface, to large earthquakes (M > 5) that pose a serious risk to neighboring populations and may lead to the abandon of geothermal projects. In this context, it is of paramount importance to: i) better characterize and understand the interactions between natural and anthropogenic factors which may lead to geothermal-induced seismicity and ii) evaluate currently applied approaches to handle and minimize associated risks.</p><p>The objective of this work is to establish a state of the art about deep geothermal-induced seismicity, by describing factors that have a bearing on the generation of seismic events, as well as by discussing existing means to handle their occurrence. Based on a worldwide review of geothermal projects, we created a large database describing each selected case study in terms of geological properties and tectonic setting, operational parameters and type of geothermal systems, as well as spatio-temporal characteristics of the observed induced seismicity. Collected data are analyzed in order to better understand possible cause-effect relationships between induced seismicity and geothermal operations with the aim of identifying the most important preexisting and anthropogenic factors, as well as their interactions, which may have a key role on the occurrence of seismic activity.       </p>
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