In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essent... more In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essential to determine the controls of the deformation within the upper plate and the dip angle of the subducting lithosphere. In this study, we evaluate the degree of influence of both the configuration of the upper plate and variations of the subduction angle on the lithospheric thermal field of the southern Central Andes (29°–39°S). Here, the subduction angle increases from subhorizontal (5°) north of 33°S, to steep (~30°) in the south. We derived the 3D temperature and heat flow distribution of the lithosphere in the southern Central Andes considering conversion of S wave tomography to temperatures together with steady-state conductive modeling. We found that the orogen is overall warmer than the forearc and the foreland, and that the lithosphere of the northern part of the foreland appears colder than its southern counterpart. Sedimentary blanketing and the thickness of the radiogenic cru...
Realistic modelling of tightly coupled hydrogeomechanical processes is relevant for the assessmen... more Realistic modelling of tightly coupled hydrogeomechanical processes is relevant for the assessment of many hydrological and geotechnical applications. Such processes occur in geologic formations and are influenced by natural heterogeneity. Current numerical libraries offer capabilities and physics couplings that have proven to be valuable in many geotechnical fields like gas storage, rock fracturing and Earth resources extraction. However, implementation and verification of the full heterogeneity of subsurface properties using high-resolution field data in coupled simulations has not been done before. We develop, verify and document RHEA (Real HEterogeneity App), an open-source, fully coupled, finite-element application capable of including element-resolution hydro-geomechanical properties in coupled simulations. To extend current modelling capabilities of the Multiphysics Object-Oriented Simulation Environment (MOOSE), we added new code that handles spatially distributed data of all hydro-geomechanical properties. We further propose a simple yet powerful workflow to facilitate the incorporation of such data to MOOSE. We then verify RHEA with analytical solutions in one and two dimensions and propose a benchmark semi-analytical problem to verify heterogeneous systems with sharp gradients. Finally, we demonstrate RHEA's capabilities with a comprehensive example including realistic properties. With this we demonstrate that RHEA is a verified open-source application able to include complex geology to perform scalable, fully coupled, hydrogeomechanical simulations. Our work is a valuable tool to assess challenging real-world hydro-geomechanical systems that may include different levels of complexity like heterogeneous geology and sharp gradients produced by contrasting subsurface properties.
The North Patagonian Massif (NPM) area in Argentina includes a plateau of 1200 m a.s.l. (meters a... more The North Patagonian Massif (NPM) area in Argentina includes a plateau of 1200 m a.s.l. (meters above sea level) average height, which is 500–700 m higher than its surrounding areas. The plateau shows no evidence of internal deformation, while the surrounding basins have been deformed during Cenozoic orogenic events. Previous works suggested that the plateau formation was caused by a lithospheric uplift event during the Paleogene. However, the causative processes responsible for the plateau origin and its current state remain speculative. To address some of these questions, we carried out 3D lithospheric-scale steady-state and transient thermal simulations of the NPM and its surroundings, as based on an existing 3D geological model of the area. Our results are indicative of a thicker and warmer lithosphere below the NPM plateau compared with its surroundings, suggesting that the plateau is still isostatically buoyant and thus explaining its present-day elevation. The transient therm...
Seismic attenuation and rheology of crustal rocks: results from numerical tests
<p>Seismic attenuation of the rocks mainly depends on their intrins... more <p>Seismic attenuation of the rocks mainly depends on their intrinsic anelasticity, which is the dissipation of seismic energy as it propagates through the medium. Several studies have already demonstrated that seismic attenuation, described by the Q-factor, is intrinsically related to the rocks’ viscosity, considering their common dependency on composition, grain size, fluid content, and T-P conditions. However, viscous deformation of the rocks occurs through different mechanisms: diffusion creep, numerous mechanisms of the dislocation creep, pressure solution, which are expressed by several Arrhenius-type constitutive laws. This makes more complex the investigation of quantitative relationships between seismic attenuation and viscous rocks' rheology.</p><p>The main purpose of this study is to investigate the mutual dependence of the seismic attenuation and viscous deformation of the crustal rocks. To this aim, we performed several numerical tests to check the variability of some physical properties (e.g., elastic modulus, Poisson’s ratio) and improve the existing relationships between seismic attenuation and viscous deformation of several natural rock samples. The Burgers mechanical model and Arrhenius relation are included in these test series to achieve a closer approximation of the rocks’ viscous deformation.</p><p>In this way, it will be possible to predict the viscous rheology of rocks from the laws describing the seismic attenuation and viceversa. The obtained results will be used to (1) constrain the Q-factor and rheological (creep) parameters, which are still subjected to high uncertainties, (2) validate/modify the existing seismic attenuation and rheological laws, (3) increase the robustness of the geodynamic and rocks’ mechanics numerical codes and our understanding of the role that rocks’ rheology exerts on the tectonic processes.</p>
A successful utilization of deep geothermal resources requires accurate predictions about the dis... more A successful utilization of deep geothermal resources requires accurate predictions about the distribution of reservoir temperature as well as of the hydraulic processes exerting a direct influence on the productivity of geothermal reservoirs. The aim of this study was to investigate and quantify the influence that regional thermo-hydraulic processes have on the geothermal configuration of potential reservoirs in the German Federal State of Hesse. Specifically, we have addressed the question of how the regional thermal and hydraulic configuration influence the local hydro-thermal reservoir conditions. Therefore, a 3D structural model of Hesse was used as a basis for purely hydraulic, purely thermal and coupled 3D thermo-hydraulic simulations of the deep fluid flow and heat transport. As a result of our numerical simulations, Hesse can be differentiated into sub-areas differing in terms of the dominating heat transport process. In a final attempt to quantify the robustness and reliab...
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
We present three-dimensional (3-D) models that describe the present-day thermal and rheological s... more We present three-dimensional (3-D) models that describe the present-day thermal and rheological state of the lithosphere of the greater Kenya rift region aiming at a better understanding of the rift evolution, with a particular focus on plume-lithosphere interactions. The key methodology applied is the 3-D integration of diverse geological and geophysical observations using gravity modelling. Accordingly, the resulting lithospheric-scale 3-D density model is consistent with (i) reviewed descriptions of lithological variations in the sedimentary and volcanic cover, (ii) known trends in crust and mantle seismic velocities as revealed by seismic and seismological data and (iii) the observed gravity field. This data-based model is the first to image a 3-D density configuration of the crystalline crust for the entire region of Kenya and northern Tanzania. An upper and a basal crustal layer are differentiated, each composed of several domains of different average densities. We interpret these domains to trace back to the Precambrian terrane amalgamation associated with the East African Orogeny and to magmatic processes during Mesozoic and Cenozoic rifting phases. In combination with seismic velocities, the densities of these crustal domains indicate compositional differences. The derived lithological trends have been used to parameterise steady-state thermal and rheological models. These models indicate that crustal and mantle temperatures decrease from the Kenya rift in the west to eastern Kenya, while the integrated strength of the lithosphere increases. Thereby, the detailed strength configuration appears strongly controlled by the complex inherited crustal structure, which may have been decisive for the onset, localisation and propagation of rifting.
Theory and numerical implementation describing groundwater flow and the transport of heat and sol... more Theory and numerical implementation describing groundwater flow and the transport of heat and solute mass in fully saturated fractured rocks with elasto-plastic mechanical feedbacks are developed. In our formulation, fractures are considered as being of lower dimension than the hosting deformable porous rock and we consider their hydraulic and mechanical apertures as scaling parameters to ensure continuous exchange of fluid mass and energy within the fracture-solid matrix system. The coupled system of equations is implemented into a new simulator code that makes use of a Galerkin Finite Element technique. The code builds on a flexible, object oriented numerical framework (MOOSE, Multiphysics Object Oriented Simulation Environment) which provides an extensive scalable parallel, implicit coupling to solve for the multiphysics problem. The governing equations of groundwater flow, heat and mass transport and rock deformation are solved in a weak sense (either by classical Newton- Raphso...
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
The recent structural setting of the North East German Basin is mainly controlled by the presence... more The recent structural setting of the North East German Basin is mainly controlled by the presence of a thick sequence of Zechstein salt acting as a decoupling horizon between the Mesozoic and Cenozoic strata and the Upper Permian pre-Zechstein sediments. Apart from affecting the structural evolution of the basin, the salt structures locally modify the regional geothermal field. These interactions
The goal of the present study is to investigate and quantify the main physical processes and para... more The goal of the present study is to investigate and quantify the main physical processes and parameters affecting the regional thermal setting within the North East German Basin (NEGB) by means of 3D numerical simulations. The NEGB is structurally controlled by the presence of a thick sequence of Upper Permian Zechstein salt acting as a decoupling horizon between the Mesozoic
Shallow and deep control on the thermal structure of basins as inferred by 3 D numerical models - an example from the North East German Basin
Numerical simulations are carried out to characterize the regional thermal structure of the North... more Numerical simulations are carried out to characterize the regional thermal structure of the North East German Basin (NEGB) and its interaction with the basin-scale active fluid system. The aim of the study is to provide deeper insights on the relevant processes influencing the hydrothermal setting of the basin in a way that will help to constrain the potential geothermal resources
In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essent... more In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essential to determine the controls of the deformation within the upper plate and the dip angle of the subducting lithosphere. In this study, we evaluate the degree of influence of both the configuration of the upper plate and variations of the subduction angle on the lithospheric thermal field of the southern Central Andes (29°–39°S). Here, the subduction angle increases from subhorizontal (5°) north of 33°S, to steep (~30°) in the south. We derived the 3D temperature and heat flow distribution of the lithosphere in the southern Central Andes considering conversion of S wave tomography to temperatures together with steady-state conductive modeling. We found that the orogen is overall warmer than the forearc and the foreland, and that the lithosphere of the northern part of the foreland appears colder than its southern counterpart. Sedimentary blanketing and the thickness of the radiogenic cru...
Realistic modelling of tightly coupled hydrogeomechanical processes is relevant for the assessmen... more Realistic modelling of tightly coupled hydrogeomechanical processes is relevant for the assessment of many hydrological and geotechnical applications. Such processes occur in geologic formations and are influenced by natural heterogeneity. Current numerical libraries offer capabilities and physics couplings that have proven to be valuable in many geotechnical fields like gas storage, rock fracturing and Earth resources extraction. However, implementation and verification of the full heterogeneity of subsurface properties using high-resolution field data in coupled simulations has not been done before. We develop, verify and document RHEA (Real HEterogeneity App), an open-source, fully coupled, finite-element application capable of including element-resolution hydro-geomechanical properties in coupled simulations. To extend current modelling capabilities of the Multiphysics Object-Oriented Simulation Environment (MOOSE), we added new code that handles spatially distributed data of all hydro-geomechanical properties. We further propose a simple yet powerful workflow to facilitate the incorporation of such data to MOOSE. We then verify RHEA with analytical solutions in one and two dimensions and propose a benchmark semi-analytical problem to verify heterogeneous systems with sharp gradients. Finally, we demonstrate RHEA's capabilities with a comprehensive example including realistic properties. With this we demonstrate that RHEA is a verified open-source application able to include complex geology to perform scalable, fully coupled, hydrogeomechanical simulations. Our work is a valuable tool to assess challenging real-world hydro-geomechanical systems that may include different levels of complexity like heterogeneous geology and sharp gradients produced by contrasting subsurface properties.
The North Patagonian Massif (NPM) area in Argentina includes a plateau of 1200 m a.s.l. (meters a... more The North Patagonian Massif (NPM) area in Argentina includes a plateau of 1200 m a.s.l. (meters above sea level) average height, which is 500–700 m higher than its surrounding areas. The plateau shows no evidence of internal deformation, while the surrounding basins have been deformed during Cenozoic orogenic events. Previous works suggested that the plateau formation was caused by a lithospheric uplift event during the Paleogene. However, the causative processes responsible for the plateau origin and its current state remain speculative. To address some of these questions, we carried out 3D lithospheric-scale steady-state and transient thermal simulations of the NPM and its surroundings, as based on an existing 3D geological model of the area. Our results are indicative of a thicker and warmer lithosphere below the NPM plateau compared with its surroundings, suggesting that the plateau is still isostatically buoyant and thus explaining its present-day elevation. The transient therm...
Seismic attenuation and rheology of crustal rocks: results from numerical tests
<p>Seismic attenuation of the rocks mainly depends on their intrins... more <p>Seismic attenuation of the rocks mainly depends on their intrinsic anelasticity, which is the dissipation of seismic energy as it propagates through the medium. Several studies have already demonstrated that seismic attenuation, described by the Q-factor, is intrinsically related to the rocks’ viscosity, considering their common dependency on composition, grain size, fluid content, and T-P conditions. However, viscous deformation of the rocks occurs through different mechanisms: diffusion creep, numerous mechanisms of the dislocation creep, pressure solution, which are expressed by several Arrhenius-type constitutive laws. This makes more complex the investigation of quantitative relationships between seismic attenuation and viscous rocks' rheology.</p><p>The main purpose of this study is to investigate the mutual dependence of the seismic attenuation and viscous deformation of the crustal rocks. To this aim, we performed several numerical tests to check the variability of some physical properties (e.g., elastic modulus, Poisson’s ratio) and improve the existing relationships between seismic attenuation and viscous deformation of several natural rock samples. The Burgers mechanical model and Arrhenius relation are included in these test series to achieve a closer approximation of the rocks’ viscous deformation.</p><p>In this way, it will be possible to predict the viscous rheology of rocks from the laws describing the seismic attenuation and viceversa. The obtained results will be used to (1) constrain the Q-factor and rheological (creep) parameters, which are still subjected to high uncertainties, (2) validate/modify the existing seismic attenuation and rheological laws, (3) increase the robustness of the geodynamic and rocks’ mechanics numerical codes and our understanding of the role that rocks’ rheology exerts on the tectonic processes.</p>
A successful utilization of deep geothermal resources requires accurate predictions about the dis... more A successful utilization of deep geothermal resources requires accurate predictions about the distribution of reservoir temperature as well as of the hydraulic processes exerting a direct influence on the productivity of geothermal reservoirs. The aim of this study was to investigate and quantify the influence that regional thermo-hydraulic processes have on the geothermal configuration of potential reservoirs in the German Federal State of Hesse. Specifically, we have addressed the question of how the regional thermal and hydraulic configuration influence the local hydro-thermal reservoir conditions. Therefore, a 3D structural model of Hesse was used as a basis for purely hydraulic, purely thermal and coupled 3D thermo-hydraulic simulations of the deep fluid flow and heat transport. As a result of our numerical simulations, Hesse can be differentiated into sub-areas differing in terms of the dominating heat transport process. In a final attempt to quantify the robustness and reliab...
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
We present three-dimensional (3-D) models that describe the present-day thermal and rheological s... more We present three-dimensional (3-D) models that describe the present-day thermal and rheological state of the lithosphere of the greater Kenya rift region aiming at a better understanding of the rift evolution, with a particular focus on plume-lithosphere interactions. The key methodology applied is the 3-D integration of diverse geological and geophysical observations using gravity modelling. Accordingly, the resulting lithospheric-scale 3-D density model is consistent with (i) reviewed descriptions of lithological variations in the sedimentary and volcanic cover, (ii) known trends in crust and mantle seismic velocities as revealed by seismic and seismological data and (iii) the observed gravity field. This data-based model is the first to image a 3-D density configuration of the crystalline crust for the entire region of Kenya and northern Tanzania. An upper and a basal crustal layer are differentiated, each composed of several domains of different average densities. We interpret these domains to trace back to the Precambrian terrane amalgamation associated with the East African Orogeny and to magmatic processes during Mesozoic and Cenozoic rifting phases. In combination with seismic velocities, the densities of these crustal domains indicate compositional differences. The derived lithological trends have been used to parameterise steady-state thermal and rheological models. These models indicate that crustal and mantle temperatures decrease from the Kenya rift in the west to eastern Kenya, while the integrated strength of the lithosphere increases. Thereby, the detailed strength configuration appears strongly controlled by the complex inherited crustal structure, which may have been decisive for the onset, localisation and propagation of rifting.
Theory and numerical implementation describing groundwater flow and the transport of heat and sol... more Theory and numerical implementation describing groundwater flow and the transport of heat and solute mass in fully saturated fractured rocks with elasto-plastic mechanical feedbacks are developed. In our formulation, fractures are considered as being of lower dimension than the hosting deformable porous rock and we consider their hydraulic and mechanical apertures as scaling parameters to ensure continuous exchange of fluid mass and energy within the fracture-solid matrix system. The coupled system of equations is implemented into a new simulator code that makes use of a Galerkin Finite Element technique. The code builds on a flexible, object oriented numerical framework (MOOSE, Multiphysics Object Oriented Simulation Environment) which provides an extensive scalable parallel, implicit coupling to solve for the multiphysics problem. The governing equations of groundwater flow, heat and mass transport and rock deformation are solved in a weak sense (either by classical Newton- Raphso...
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
The recent structural setting of the North East German Basin is mainly controlled by the presence... more The recent structural setting of the North East German Basin is mainly controlled by the presence of a thick sequence of Zechstein salt acting as a decoupling horizon between the Mesozoic and Cenozoic strata and the Upper Permian pre-Zechstein sediments. Apart from affecting the structural evolution of the basin, the salt structures locally modify the regional geothermal field. These interactions
The goal of the present study is to investigate and quantify the main physical processes and para... more The goal of the present study is to investigate and quantify the main physical processes and parameters affecting the regional thermal setting within the North East German Basin (NEGB) by means of 3D numerical simulations. The NEGB is structurally controlled by the presence of a thick sequence of Upper Permian Zechstein salt acting as a decoupling horizon between the Mesozoic
Shallow and deep control on the thermal structure of basins as inferred by 3 D numerical models - an example from the North East German Basin
Numerical simulations are carried out to characterize the regional thermal structure of the North... more Numerical simulations are carried out to characterize the regional thermal structure of the North East German Basin (NEGB) and its interaction with the basin-scale active fluid system. The aim of the study is to provide deeper insights on the relevant processes influencing the hydrothermal setting of the basin in a way that will help to constrain the potential geothermal resources
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Papers by Mauro Cacace