Birgit Müller | Karlsruhe Institute of Technology (KIT) (original) (raw)

Papers by Birgit Müller

Eos, Transactions American Geophysical Union, 2004

International Journal of Rock Mechanics and Mining Sciences, 2010

Pore pressure/stress coupling is the change in the smaller horizontal stress associated with chan... more Pore pressure/stress coupling is the change in the smaller horizontal stress associated with changes in pore pressure , and has been measured in numerous reservoirs worldwide. These measurements suggest that the change in minimum horizontal stress ∆ is on average ca. 64% of the change in the reservoir pore pressure ∆ , but can be as low as 34% and as high as 118%. Conventionally it is assumed that the total vertical stress , given by the overburden, is not affected by changes in pore pressure, in contrast to the horizontal stresses and. We investigate analytically and numerically the spatio-temporal pore pressure and stress evolution in poroelastic media for continuous fluid injection at a point source, and calculate from the numerical modelling results the ratio ∆ /∆. Analytically, we show that the measured average of ∆ /∆ can mathematically be deduced from the longterm limit of the spatio-temporal evolution of pore pressure and horizontal stress caused by fluid injection at a point source. We compare our numerical results to the analytical solution for continuous point injection into homogeneous poroelastic media as well as to ∆ /∆ values measured in the field, and show that all stress components change with a variation in. We use the concept of poroelasticity to explain the observed coupling between pore pressure and stress in reservoirs, and we consider different measurement locations and measurement times as one possible reason for the measured variation in ∆ /∆ in different oil fields worldwide.

AIP Conference Proceedings, 2006

The world stress map-a freely accessible tool for geohazard assessment, Recent Geodynamics Georis... more The world stress map-a freely accessible tool for geohazard assessment, Recent Geodynamics Georisk and

Geothermics, 2014

The spatio-temporal changes of the stress state in a geothermal reservoir are of key importance f... more The spatio-temporal changes of the stress state in a geothermal reservoir are of key importance for the understanding of induced seismicity and planning of injection and depletion strategies. In particular the poro-elastic effects on the stress state due to re-injection or depletion of water are of interest for both geothermal projects and hydrocarbon exploitation. In addition to the conventionally used effective stress concept, poro-elasticity affects the stress tensor components differently as a function of changes in pore pressure. Here, we provide an analytical base for the long-term changes of the 3D stress tensor components as a function of pore pressure changes. Results indicate that for a constant rate of injection or depletion the coupling between pore pressure and all stress tensor components depends on the location in the reservoir with respect to the reinjection/depletion point as well as the time since the beginning of pore pressure changes. Our systematic analysis suggests that poro-elastic stress changes can even locally modify the given tectonic stress regime. Furthermore, the results predict that localized changes of maximum shear stress can lead to different fracture orientations than those expected when poro-elastic effects are not considered. These results indicate a need for 3D geomechanical-numerical studies of more realistic reservoir settings in order to study the 3D effects of pore pressure/stress coupling. Our generic 3D geomechanical-numerical study shows that less than two years of production of a single well changes shear stresses by 0.2 MPa. Thus, in reservoirs with decades of production shear stress change can reach sufficiently high values to reactivate pre-existing faults or even generate new fractures with unexpected orientations.

Geothermal Energy, 2015

Background: The characterization of fault zones in the Bavarian Molasse Basin plays a major role ... more Background: The characterization of fault zones in the Bavarian Molasse Basin plays a major role for further geothermal reservoir development. Hence, their identification, geological origin, and hydraulic characterization are discussed extensively. Methods: Stress indicators and fractures are interpreted from image and caliper logs of three highly deviated wells at the Sauerlach site. We transform the identified stress field into the borehole coordinate system and compare the observed orientation to the modeled stress field which assumes a homogeneous borehole surrounding. Results: High breakout occurrence, cross-cutting fractures, and a fracture orientation from N-S to NNE-SSW are observed in Sauerlach Th1. In Sauerlach Th2 and Th3, fractures strike primarily ENE-WSW and N-S to NNE-SSW. Drilling-enhanced natural fractures and drilling-induced tensile fractures are observed in all three wells and indicate the orientation of tensile stress at the borehole wall. In Sauerlach Th2 and Th3, stress transformation indicates a S H-dir.~N 10°E in a strike-slip stress regime. The modeled stress orientations match the observed orientations within the well Sauerlach Th1 if either S H-dir. is N 320°E in a strike-slip regime or S H-dir. is N 10°E in a normal faulting regime. Conclusion: This approach improves the detection of the local stress field especially for non-vertical wells, which has, in combination with the facture pattern, a major impact on the hydraulic system of the geothermal reservoir.

International Journal of Rock Mechanics and Mining Sciences, 2014

Breakouts are commonly used as principal indicator of stress orientation. However, variation of b... more Breakouts are commonly used as principal indicator of stress orientation. However, variation of breakout orientation with depth, especially in the vicinity of fracture zones, is frequently observed. This study describes a systematic analysis of breakout occurrence, variation of breakout orientation and fracture characteristics. We infer the impact of fracture networks on the development of breakouts from detailed analysis of 1221 borehole elongation pairs in the vicinity of 1871 natural fractures observed in the crystalline section of the GPK4 well of the Soultz-sous-Forêts geothermal field (France). Breakout orientation anomalies are found to concentrate in the immediate vicinity of fault cores and to decrease with distance to the fault core. Patterns of breakout orientation in the vicinity of natural fractures suggest that the breakout rotation, relative to the mean S hmin direction, is strongly influenced by the fracture orientation. Even a direct relationship between fracture and breakout orientations is found in some depth intervals. In highly fractured zones, with different fracture families present, breakout orientations are especially heterogeneous, resulting from the overlapping effects of the fracture network. Additionally, breakouts are typically found to be asymmetrical in zones with high fracture density. Borehole breakout heterogeneities do not seem to be related to the principal stress heterogeneity only, but also to the effect of mechanical heterogeneities like weak zones with different elastic moduli, rock strength and fracture patterns. Consequently, care has to be taken when inferring the principal stress orientation from borehole breakout data observed in fractured rock.

Solid Earth

The contemporary stress state in the upper crust is of great interest for geotechnical applicatio... more The contemporary stress state in the upper crust is of great interest for geotechnical applications and basic research alike. However, our knowledge of the crustal stress field from the data perspective is limited. For Germany basically two datasets are available: orientations of the maximum horizontal stress (S Hmax) and the stress regime as part of the World Stress Map (WSM) database as well as a complementary compilation of stress magnitude data of Germany and adjacent regions. However, these datasets only provide pointwise, incomplete and heterogeneous information of the 3D stress tensor. Here, we present a geomechanical-numerical model that provides a continuous description of the contemporary 3D crustal stress state on a regional scale for Germany. The model covers an area of about 1000 × 1250 km 2 and extends to a depth of 100 km containing seven units, with specific material properties (density and elastic rock properties) and laterally varying thicknesses: a sedimentary unit, four different units of the upper crust, the lower crust and the lithospheric mantle. The model is calibrated by the two datasets to achieve a best-fit regarding the S Hmax orientations and the minimum horizontal stress magnitudes (S hmin). The modeled orientations of S Hmax are almost entirely within the uncertainties of the WSM data used and the S hmin magnitudes fit to various datasets well. Only the S Hmax magnitudes show locally significant deviations, primarily indicating values that are too low in the lower part of the model. The model is open for further refinements regarding model geometry, e.g., additional layers with laterally varying material properties, and incorporation of future stress measurements. In addition, it can provide the initial stress state for local geomechanical models with a higher resolution.

Safety of Nuclear Waste Disposal

Geothermal Energy

Knowledge of the crustal stress state is important for the assessment of subsurface stability. In... more Knowledge of the crustal stress state is important for the assessment of subsurface stability. In particular, stress magnitudes are essential for the calibration of geomechanical models that estimate a continuous description of the 3-D stress field from pointwise and incomplete stress data. Well established is the World Stress Map Project, a global and publicly available database for stress orientations, but for stress magnitude data only local data collections are available. Herein, we present the first comprehensive and open-access stress magnitude database for Germany and adjacent regions, consisting of 568 data records. In addition, we introduce a quality ranking scheme for stress magnitude data for the first time.

Marine and Petroleum Geology

Abstract Understanding the orientation and connectivity of fracture systems in tight reservoirs i... more Abstract Understanding the orientation and connectivity of fracture systems in tight reservoirs is essential to reduce uncertainties in reservoir development and production. However, the actual flow potential of the fractures can be controlled by the present-day stress field. Dilation- and slip tendency analyses can improve fracture permeability evaluations and thus, aid in estimating the hydrocarbon recovery of a field. This study focuses on a naturally-fractured, relatively tight (matrix permeabilities of 0.01–1 mD) and gas-producing Late Permian (Zechstein) reservoir in the Southern Permian Basin, northern Germany. Fracture data are obtained from resistivity image log data of a 775 m long horizontal well, and show principal NE – SW orientation with main dip angles steeper than 70°. To quantify the potential of those fractures that contribute to the flow within the reservoir, dilation (Td)- and slip (Ts) tendencies are calculated. Two different stress scenarios are defined based on known variations in the orientation of the horizontal stresses between formations below and above the Zechstein salt in an offset field approximately 5 km away. Results of Td and Ts strongly depend on the strike and dip angle of the fractures, with sub-vertical fractures showing highest potential to dilate while fractures with dip angles of 60° are favorably oriented for slip. Fractures with orientations parallel to the principal horizontal stress have highest slip- and dilation tendencies. Adding this information to the calculation of fracture permeability results in a significant reduction of the calculated flow potential due to the influence of the stress field. Thus, incorporating stress field data helps reducing risks in field development planning.

Recent findings from regional and local seismic tomography studies together with ex- tremely high... more Recent findings from regional and local seismic tomography studies together with ex- tremely high intermediate-depth seismicity in the Vrancea region point towards the interpretation that lithospheric slab, descending beneath the southeastern Carpathians, approaches a stage of break-off. To understand processes of stress generation in the descending slab, we analysed stress in the slab by means of analytical and numerical modeling. We found an analytical solution for the stress magnitude at various angles of slab subduction. We developed a two-dimensional thermo-mechanical finite-element model of a slab sinking in the mantle due to gravity and overlain by the continental crust. The model predicts (a) downward extension in the slab as inferred from the stress axes of earthquakes, (b) the maximum stress occurring in the depth range of 80 km to 180 km, and (c) the minimum stress falling into the depth range of 40 km to 80 km. The results are robust in respect to various geometrical str...

Abstract. The contemporary stress state in the upper crust is of great interest for geotechnical ... more Abstract. The contemporary stress state in the upper crust is of great interest for geotechnical applications and basic research likewise. However, our knowledge of the crustal stress field from the data perspective is limited. For Western Central Europe basically two datasets are available: Orientations of the maximum horizontal stress (SHmax) and the stress regime as part of the World Stress Map (WSM) database (Heidbach et al., 2018) as well as a complementary compilation of stress magnitude data of Germany and adjacent regions (Morawietz et al., 2020). However, these datasets only provide pointwise, incomplete and heterogeneous information of the 3D stress tensor. Here, we present a geomechanical-numerical model that provides a continuous description of the contemporary 3D crustal stress state on a regional scale for Western Central Europe. The model covers an area of about 1000 × 1250 km2 and extends to a depth of 100 km containing seven lithostratigraphic units, with specific m...

Geophysical Journal International, 2010

We model microseismicity triggered by fluid injection on the basis of the theory of poroelasticit... more We model microseismicity triggered by fluid injection on the basis of the theory of poroelasticity accounting for the external stress field. Consideration of the fully coupled poroelastic field equations enables us to apply a Coulomb failure criterion using pore fluid pressure and stress tensor as well as the coefficient of friction. The poroelastic fields are calculated with the finite-element method simulating fluid injection with constant injection rate into a 2-D domain. The influence of diffusivity, injection rate and stress field on the occurrence of microseismicity is analysed and compared to simulations based on pore fluid pressure diffusion only. We show that an anisotropic initial stress field causes elongated microseismic clouds. These clouds are indistinguishable from those generated in poroelastic solids under isotropic stress but exhibiting anisotropic hydraulic diffusivity. This similarity shows that microseismicity distributions dependent on both, the hydraulic properties and the coupling of pore fluid pressure to the stress field. In particular, neglecting the influence of the external stress field may lead to overestimation of the anisotropy of diffusivity tensor components. Furthermore, the results of our numerical simulations are strongly sensitive to changes of fluid injection rate.

Eos, Transactions American Geophysical Union, 2004

Terra Nova, 1996

The Tornquist Fan, a fan-shaped region in Denmark and Western Baltic, is situated in the transiti... more The Tornquist Fan, a fan-shaped region in Denmark and Western Baltic, is situated in the transition zone between the Western and Northern European Stress Provinces. Breakout data from 20 wells (0.3–3.6 km) were analysed. The fan can be divided into three stress provinces: (i) The area south of the Rømø Fracture Zone is part of the Western European Stress Province and has NNW-SSE orientation of the maximum horizontal stress, (ii) The sediment cover in the Nonvegian-Danish Basin is dominated by ENE-WSW orientated maximum horizontal stress, (iii) The maximum horizontal stress is sub-parallel to the strike of the Sorgenfrei-Tornquist Zone. Deviations from the regional stress field were observed in wells close to faults and salt diapirs. In wells south of the Sorgenfrei-Tornquist Zone, breakout occurrence decreases with increasing age of the stratigraphic units. The downhole breakout distribution seems to correlate with lithology and thickness of the sediment layer.

Philosophical Transactions of The Royal Society B: Biological Sciences, 1991

Physical Chemistry Chemical Physics, 2002

A wetted-wall cylindrical flow reactor was used to measure uptake coefficients, g, of O 3 on aque... more A wetted-wall cylindrical flow reactor was used to measure uptake coefficients, g, of O 3 on aqueous surfaces at 293 K. The loss of O 3 from the gas-phase following contact with varying areas of aqueous surface was determined by UV absorption. The use of Na 2 S 2 O 3 as an aqueous-phase scavenger for O 3 ensured that uptake coefficients were in a reaction-controlled rather than mass accommodation-controlled regime. Observed uptake coefficients were corrected for radial gas-diffusion to yield values of g corr . From extrapolation of a plot of 1/g corr against the inverse square-root of the Na 2 S 2 O 3 activity, a value of a ¼ 4 Â 10 À2 was derived for the true mass accommodation coefficient of O 3 . Evaluation of uncertainties indicate a conservative lower limit of 10 À2 for a. The data do not rule out that the upper limit approaches unity. However, it is shown that the measured value of a is sufficiently high that mass accommodation does not limit heterogeneous processing of O 3 in the atmosphere for droplets of diameter >10 mm. A value of 3.7 þ0:7 À0:6 Â 10 8 L mol À1 s À1 is derived for the aqueous-phase reaction rate coefficient between O 3 and Na 2 S 2 O 3 at 293 K.

Eos, Transactions American Geophysical Union, 2004

International Journal of Rock Mechanics and Mining Sciences, 2010

Pore pressure/stress coupling is the change in the smaller horizontal stress associated with chan... more Pore pressure/stress coupling is the change in the smaller horizontal stress associated with changes in pore pressure , and has been measured in numerous reservoirs worldwide. These measurements suggest that the change in minimum horizontal stress ∆ is on average ca. 64% of the change in the reservoir pore pressure ∆ , but can be as low as 34% and as high as 118%. Conventionally it is assumed that the total vertical stress , given by the overburden, is not affected by changes in pore pressure, in contrast to the horizontal stresses and. We investigate analytically and numerically the spatio-temporal pore pressure and stress evolution in poroelastic media for continuous fluid injection at a point source, and calculate from the numerical modelling results the ratio ∆ /∆. Analytically, we show that the measured average of ∆ /∆ can mathematically be deduced from the longterm limit of the spatio-temporal evolution of pore pressure and horizontal stress caused by fluid injection at a point source. We compare our numerical results to the analytical solution for continuous point injection into homogeneous poroelastic media as well as to ∆ /∆ values measured in the field, and show that all stress components change with a variation in. We use the concept of poroelasticity to explain the observed coupling between pore pressure and stress in reservoirs, and we consider different measurement locations and measurement times as one possible reason for the measured variation in ∆ /∆ in different oil fields worldwide.

AIP Conference Proceedings, 2006

The world stress map-a freely accessible tool for geohazard assessment, Recent Geodynamics Georis... more The world stress map-a freely accessible tool for geohazard assessment, Recent Geodynamics Georisk and

Geothermics, 2014

The spatio-temporal changes of the stress state in a geothermal reservoir are of key importance f... more The spatio-temporal changes of the stress state in a geothermal reservoir are of key importance for the understanding of induced seismicity and planning of injection and depletion strategies. In particular the poro-elastic effects on the stress state due to re-injection or depletion of water are of interest for both geothermal projects and hydrocarbon exploitation. In addition to the conventionally used effective stress concept, poro-elasticity affects the stress tensor components differently as a function of changes in pore pressure. Here, we provide an analytical base for the long-term changes of the 3D stress tensor components as a function of pore pressure changes. Results indicate that for a constant rate of injection or depletion the coupling between pore pressure and all stress tensor components depends on the location in the reservoir with respect to the reinjection/depletion point as well as the time since the beginning of pore pressure changes. Our systematic analysis suggests that poro-elastic stress changes can even locally modify the given tectonic stress regime. Furthermore, the results predict that localized changes of maximum shear stress can lead to different fracture orientations than those expected when poro-elastic effects are not considered. These results indicate a need for 3D geomechanical-numerical studies of more realistic reservoir settings in order to study the 3D effects of pore pressure/stress coupling. Our generic 3D geomechanical-numerical study shows that less than two years of production of a single well changes shear stresses by 0.2 MPa. Thus, in reservoirs with decades of production shear stress change can reach sufficiently high values to reactivate pre-existing faults or even generate new fractures with unexpected orientations.

Geothermal Energy, 2015

Background: The characterization of fault zones in the Bavarian Molasse Basin plays a major role ... more Background: The characterization of fault zones in the Bavarian Molasse Basin plays a major role for further geothermal reservoir development. Hence, their identification, geological origin, and hydraulic characterization are discussed extensively. Methods: Stress indicators and fractures are interpreted from image and caliper logs of three highly deviated wells at the Sauerlach site. We transform the identified stress field into the borehole coordinate system and compare the observed orientation to the modeled stress field which assumes a homogeneous borehole surrounding. Results: High breakout occurrence, cross-cutting fractures, and a fracture orientation from N-S to NNE-SSW are observed in Sauerlach Th1. In Sauerlach Th2 and Th3, fractures strike primarily ENE-WSW and N-S to NNE-SSW. Drilling-enhanced natural fractures and drilling-induced tensile fractures are observed in all three wells and indicate the orientation of tensile stress at the borehole wall. In Sauerlach Th2 and Th3, stress transformation indicates a S H-dir.~N 10°E in a strike-slip stress regime. The modeled stress orientations match the observed orientations within the well Sauerlach Th1 if either S H-dir. is N 320°E in a strike-slip regime or S H-dir. is N 10°E in a normal faulting regime. Conclusion: This approach improves the detection of the local stress field especially for non-vertical wells, which has, in combination with the facture pattern, a major impact on the hydraulic system of the geothermal reservoir.

International Journal of Rock Mechanics and Mining Sciences, 2014

Breakouts are commonly used as principal indicator of stress orientation. However, variation of b... more Breakouts are commonly used as principal indicator of stress orientation. However, variation of breakout orientation with depth, especially in the vicinity of fracture zones, is frequently observed. This study describes a systematic analysis of breakout occurrence, variation of breakout orientation and fracture characteristics. We infer the impact of fracture networks on the development of breakouts from detailed analysis of 1221 borehole elongation pairs in the vicinity of 1871 natural fractures observed in the crystalline section of the GPK4 well of the Soultz-sous-Forêts geothermal field (France). Breakout orientation anomalies are found to concentrate in the immediate vicinity of fault cores and to decrease with distance to the fault core. Patterns of breakout orientation in the vicinity of natural fractures suggest that the breakout rotation, relative to the mean S hmin direction, is strongly influenced by the fracture orientation. Even a direct relationship between fracture and breakout orientations is found in some depth intervals. In highly fractured zones, with different fracture families present, breakout orientations are especially heterogeneous, resulting from the overlapping effects of the fracture network. Additionally, breakouts are typically found to be asymmetrical in zones with high fracture density. Borehole breakout heterogeneities do not seem to be related to the principal stress heterogeneity only, but also to the effect of mechanical heterogeneities like weak zones with different elastic moduli, rock strength and fracture patterns. Consequently, care has to be taken when inferring the principal stress orientation from borehole breakout data observed in fractured rock.

Solid Earth

The contemporary stress state in the upper crust is of great interest for geotechnical applicatio... more The contemporary stress state in the upper crust is of great interest for geotechnical applications and basic research alike. However, our knowledge of the crustal stress field from the data perspective is limited. For Germany basically two datasets are available: orientations of the maximum horizontal stress (S Hmax) and the stress regime as part of the World Stress Map (WSM) database as well as a complementary compilation of stress magnitude data of Germany and adjacent regions. However, these datasets only provide pointwise, incomplete and heterogeneous information of the 3D stress tensor. Here, we present a geomechanical-numerical model that provides a continuous description of the contemporary 3D crustal stress state on a regional scale for Germany. The model covers an area of about 1000 × 1250 km 2 and extends to a depth of 100 km containing seven units, with specific material properties (density and elastic rock properties) and laterally varying thicknesses: a sedimentary unit, four different units of the upper crust, the lower crust and the lithospheric mantle. The model is calibrated by the two datasets to achieve a best-fit regarding the S Hmax orientations and the minimum horizontal stress magnitudes (S hmin). The modeled orientations of S Hmax are almost entirely within the uncertainties of the WSM data used and the S hmin magnitudes fit to various datasets well. Only the S Hmax magnitudes show locally significant deviations, primarily indicating values that are too low in the lower part of the model. The model is open for further refinements regarding model geometry, e.g., additional layers with laterally varying material properties, and incorporation of future stress measurements. In addition, it can provide the initial stress state for local geomechanical models with a higher resolution.

Safety of Nuclear Waste Disposal

Geothermal Energy

Knowledge of the crustal stress state is important for the assessment of subsurface stability. In... more Knowledge of the crustal stress state is important for the assessment of subsurface stability. In particular, stress magnitudes are essential for the calibration of geomechanical models that estimate a continuous description of the 3-D stress field from pointwise and incomplete stress data. Well established is the World Stress Map Project, a global and publicly available database for stress orientations, but for stress magnitude data only local data collections are available. Herein, we present the first comprehensive and open-access stress magnitude database for Germany and adjacent regions, consisting of 568 data records. In addition, we introduce a quality ranking scheme for stress magnitude data for the first time.

Marine and Petroleum Geology

Abstract Understanding the orientation and connectivity of fracture systems in tight reservoirs i... more Abstract Understanding the orientation and connectivity of fracture systems in tight reservoirs is essential to reduce uncertainties in reservoir development and production. However, the actual flow potential of the fractures can be controlled by the present-day stress field. Dilation- and slip tendency analyses can improve fracture permeability evaluations and thus, aid in estimating the hydrocarbon recovery of a field. This study focuses on a naturally-fractured, relatively tight (matrix permeabilities of 0.01–1 mD) and gas-producing Late Permian (Zechstein) reservoir in the Southern Permian Basin, northern Germany. Fracture data are obtained from resistivity image log data of a 775 m long horizontal well, and show principal NE – SW orientation with main dip angles steeper than 70°. To quantify the potential of those fractures that contribute to the flow within the reservoir, dilation (Td)- and slip (Ts) tendencies are calculated. Two different stress scenarios are defined based on known variations in the orientation of the horizontal stresses between formations below and above the Zechstein salt in an offset field approximately 5 km away. Results of Td and Ts strongly depend on the strike and dip angle of the fractures, with sub-vertical fractures showing highest potential to dilate while fractures with dip angles of 60° are favorably oriented for slip. Fractures with orientations parallel to the principal horizontal stress have highest slip- and dilation tendencies. Adding this information to the calculation of fracture permeability results in a significant reduction of the calculated flow potential due to the influence of the stress field. Thus, incorporating stress field data helps reducing risks in field development planning.

Recent findings from regional and local seismic tomography studies together with ex- tremely high... more Recent findings from regional and local seismic tomography studies together with ex- tremely high intermediate-depth seismicity in the Vrancea region point towards the interpretation that lithospheric slab, descending beneath the southeastern Carpathians, approaches a stage of break-off. To understand processes of stress generation in the descending slab, we analysed stress in the slab by means of analytical and numerical modeling. We found an analytical solution for the stress magnitude at various angles of slab subduction. We developed a two-dimensional thermo-mechanical finite-element model of a slab sinking in the mantle due to gravity and overlain by the continental crust. The model predicts (a) downward extension in the slab as inferred from the stress axes of earthquakes, (b) the maximum stress occurring in the depth range of 80 km to 180 km, and (c) the minimum stress falling into the depth range of 40 km to 80 km. The results are robust in respect to various geometrical str...

Abstract. The contemporary stress state in the upper crust is of great interest for geotechnical ... more Abstract. The contemporary stress state in the upper crust is of great interest for geotechnical applications and basic research likewise. However, our knowledge of the crustal stress field from the data perspective is limited. For Western Central Europe basically two datasets are available: Orientations of the maximum horizontal stress (SHmax) and the stress regime as part of the World Stress Map (WSM) database (Heidbach et al., 2018) as well as a complementary compilation of stress magnitude data of Germany and adjacent regions (Morawietz et al., 2020). However, these datasets only provide pointwise, incomplete and heterogeneous information of the 3D stress tensor. Here, we present a geomechanical-numerical model that provides a continuous description of the contemporary 3D crustal stress state on a regional scale for Western Central Europe. The model covers an area of about 1000 × 1250 km2 and extends to a depth of 100 km containing seven lithostratigraphic units, with specific m...

Geophysical Journal International, 2010

We model microseismicity triggered by fluid injection on the basis of the theory of poroelasticit... more We model microseismicity triggered by fluid injection on the basis of the theory of poroelasticity accounting for the external stress field. Consideration of the fully coupled poroelastic field equations enables us to apply a Coulomb failure criterion using pore fluid pressure and stress tensor as well as the coefficient of friction. The poroelastic fields are calculated with the finite-element method simulating fluid injection with constant injection rate into a 2-D domain. The influence of diffusivity, injection rate and stress field on the occurrence of microseismicity is analysed and compared to simulations based on pore fluid pressure diffusion only. We show that an anisotropic initial stress field causes elongated microseismic clouds. These clouds are indistinguishable from those generated in poroelastic solids under isotropic stress but exhibiting anisotropic hydraulic diffusivity. This similarity shows that microseismicity distributions dependent on both, the hydraulic properties and the coupling of pore fluid pressure to the stress field. In particular, neglecting the influence of the external stress field may lead to overestimation of the anisotropy of diffusivity tensor components. Furthermore, the results of our numerical simulations are strongly sensitive to changes of fluid injection rate.

Eos, Transactions American Geophysical Union, 2004

Terra Nova, 1996

The Tornquist Fan, a fan-shaped region in Denmark and Western Baltic, is situated in the transiti... more The Tornquist Fan, a fan-shaped region in Denmark and Western Baltic, is situated in the transition zone between the Western and Northern European Stress Provinces. Breakout data from 20 wells (0.3–3.6 km) were analysed. The fan can be divided into three stress provinces: (i) The area south of the Rømø Fracture Zone is part of the Western European Stress Province and has NNW-SSE orientation of the maximum horizontal stress, (ii) The sediment cover in the Nonvegian-Danish Basin is dominated by ENE-WSW orientated maximum horizontal stress, (iii) The maximum horizontal stress is sub-parallel to the strike of the Sorgenfrei-Tornquist Zone. Deviations from the regional stress field were observed in wells close to faults and salt diapirs. In wells south of the Sorgenfrei-Tornquist Zone, breakout occurrence decreases with increasing age of the stratigraphic units. The downhole breakout distribution seems to correlate with lithology and thickness of the sediment layer.

Philosophical Transactions of The Royal Society B: Biological Sciences, 1991

Physical Chemistry Chemical Physics, 2002

A wetted-wall cylindrical flow reactor was used to measure uptake coefficients, g, of O 3 on aque... more A wetted-wall cylindrical flow reactor was used to measure uptake coefficients, g, of O 3 on aqueous surfaces at 293 K. The loss of O 3 from the gas-phase following contact with varying areas of aqueous surface was determined by UV absorption. The use of Na 2 S 2 O 3 as an aqueous-phase scavenger for O 3 ensured that uptake coefficients were in a reaction-controlled rather than mass accommodation-controlled regime. Observed uptake coefficients were corrected for radial gas-diffusion to yield values of g corr . From extrapolation of a plot of 1/g corr against the inverse square-root of the Na 2 S 2 O 3 activity, a value of a ¼ 4 Â 10 À2 was derived for the true mass accommodation coefficient of O 3 . Evaluation of uncertainties indicate a conservative lower limit of 10 À2 for a. The data do not rule out that the upper limit approaches unity. However, it is shown that the measured value of a is sufficiently high that mass accommodation does not limit heterogeneous processing of O 3 in the atmosphere for droplets of diameter >10 mm. A value of 3.7 þ0:7 À0:6 Â 10 8 L mol À1 s À1 is derived for the aqueous-phase reaction rate coefficient between O 3 and Na 2 S 2 O 3 at 293 K.