High-resolution quantitative reconstruction of Late Cretaceous-Tertiary erosion in the West Netherlands Basin using multi-formation compaction trends and seismic data: implications for geothermal exploration

A workflow is presented to determine the detailed, high-resolution pattern of erosion in maturely explored Sedimentary Basins by analysing the sonic log-based interval velocity patterns of nine stratigraphic intervals complemented by a geometrical approach involving the extrapolation of 3-D seismic reflectors. The jointly evaluated results of the two approaches not only provide important constraints on the inversion tectonics of a basin, but are also used to better constrain its maturity history and reservoir quality for geothermal energy. The developed workflow is demonstrated for the West Netherlands Basin. The pattern of erosion, which is consistent with observed subcrop maps, shows increasing amount of erosion towards the East and reflects the complex deformation of the basin, in which the reactivation of faults played a major role. Indirectly the results also indicate that continuous, syn-inversion sedimentation was taking place on the flanks of the basin during the Late Cretaceous, while its centre was characterised by non-deposition or slight erosion. For geothermal exploration the inferred variations of amount of erosion has implications for the spatial distribution of porosity which is an important parameter for the assessment of reservoir quality. © 2017, Akadémiai Kiadó

Thermo-mechanical controls on geothermal energy resources: case studies in the Pannonian Basin and other natural laboratories

Geothermal energy is an important renewable energy resource, whose share is growing rapidly in the energy mix. Geosciences provide fundamental knowledge on Earth system processes and properties, required for the development of new methods to identify prospective geothermal resources suitable for exploitation. Through robust prediction and detection of critical reservoir parameters, including rock fabric, temperature, in situ stress, flow properties and fluid geochemistry, it is possible to reduce pre-drilling risks for geothermal exploratio

3D mechanical analysis of geothermal reservoir operations in faulted sedimentary aquifers using MACRIS

Accurate and efficient predictions of three-dimensional subsurface stress changes are required for the assessment of geothermal operations with respect to fault stability and the potential risk for induced seismicity. This work extends the model capabilities of Mechanical Analysis of Complex Reservoirs for Induced Seismicity (MACRIS) to account for high-resolution thermo-elastic stress evaluations in structurally complex (i.e. faulted) and matrix permeability dominated geothermal systems. By adopting a mesh-free approach suitable to industry standard flow simulation models, MACRIS is capable of preserving the complex 3D hydraulic development of the injected cold-water volume and the 3D geometrical complexities of the reservoir model. The workflow has been applied to three-dimensional models with clastic reservoir characteristics representative for low enthalpy geothermal exploitation in the Netherlands. The models are marked by a single fault, subject to no and normal offset. Comparison of simulated stress evolutions in MACRIS with alternative analytical solutions highlight the effects of stress arching involved in the poro- and thermo-elastic stress developments on complex faults intersected by or in direct contact with the cold-water volume. Results are in agreement with previous studies and show the effect of thermal stressing to be dominant, arching of stresses to occur at the rim of the cold-water volume, and in cooling reservoirs, the intersection area of the cold-water volume in direct contact with the fault plane to be the main driver for fault reactivation and subsequent seismic potential. Moreover, results show the effects of stress arching (i) to be enhanced in the case of reservoir throw and flow compartmentalization, and (ii) to be reduced by a relative increase in conductive heat transfer between the reservoir and surrounding formations

Deep temperatures in the Paris Basin using tectonic-heat flow modelling

International audienceThe determination of deep temperatures in a basin is one of the key parameters in the exploration of geothermal energy. This study, carried out as part of the CLASTIQ-2 project, presents a 3 temperatures in the Paris Basin derived through a thermal-tectonic forward modelling method, calibrated using subsurface temperature values. The temperature dataset required for the calibration was compiled in 2007 as part of the CLASTIQ-1 project. The temperature measurement dataset is largely composed of BHT (some 2443 values). These BHT measurements required correction due to the thermal disturbance created during drilling. After correction, which was carried out using the Instantaneous Cylinder Source (ICS) method, 494 corrected BHT (BHTx) values were available for the modelling of the Paris Basin. In addition to these BHTx, some 15 DST measurements that are considered as close to the thermal equilibrium (i.e., ±5°C) were added to the temperature calibration values. According to this dataset of BHTx and DST, the average gradient in the Paris Basin was calculated as 34.9°C/km when the surface temperature is fixed at 10°C. The temperature values collected were then used to calibrate the tectonic-heat flow modelling. The model was computed at the lithospheric scale but focused on the temperature field in the sedimentary basin fill. The model takes into account the geodynamic evolution of the last 20 My, the heat production, and the specific heat conduction of each defined sedimentary layer. The result is a 3D thermal block that is presented in the form of isodepth maps. The results are strongly influenced by thermal conductivity variations such as those due to differences in sediment composition while faults create some more localised influences. The presence of anomalously radiogenic bodies beneath the basin, and/or by variations in lithosphere thickness resulting in possible heat production anomalies strongly influence the thermal variations the Paris Basin. The Alpine Orogeny created a slight temperature increase in the south-eastern part of the basin and inhomogeneities in the lithology of the basement generating additional sources of variation in the sedimentary pil

The Thor suture zone: From subduction to intraplate basin setting

The crustal seismic velocity structure of northwestern Europe shows a low P-wave velocity zone (LVZ) in the lower crust along the Caledonian Thor suture zone (TSZ) that cannot be easily attributed to Avalonia or Baltica plates abutting the TSZ. The LVZ appears to correspond to a hitherto unrecognized crustal segment (accretionary complex) that separates Avalonia from Baltica, explaining well the absence of Avalonia further east. Consequently, the northern boundary of Avalonia is shifted ∼150 km southward. Our interpretation, based on analysis of deep seismic profiles, places the LVZ in a consistent crustal domain interpretation. A comparison with present-day examples of the Kuril and Cascadia subduction zones suggests that the LVZ separating Avalonia from Baltica is composed of remnants of the Caledonian accretionary complex. If so, the present-day geometry probably originates from pre-Variscan extension and eduction during Devonian–Carboniferous backarc extension. The reinterpretation of deep crustal zonation provides a crustal framework in which the northern limit of Avalonia corresponds to the southern limit of the deep North German Basin and the northern limit of prolific gas reservoirs and late Mesozoic inversion structures

The Thor suture zone : From subduction to intraplate basin setting

The crustal seismic velocity structure of northwestern Europe shows a low P-wave velocity zone (LVZ) in the lower crust along the Caledonian Thor suture zone (TSZ) that cannot be easily attributed to Avalonia or Baltica plates abutting the TSZ. The LVZ appears to correspond to a hitherto unrecognized crustal segment (accretionary complex) that separates Avalonia from Baltica, explaining well the absence of Avalonia further east. Consequently, the northern boundary of Avalonia is shifted ∼150 km southward. Our interpretation, based on analysis of deep seismic profiles, places the LVZ in a consistent crustal domain interpretation. A comparison with present-day examples of the Kuril and Cascadia subduction zones suggests that the LVZ separating Avalonia from Baltica is composed of remnants of the Caledonian accretionary complex. If so, the present-day geometry probably originates from pre-Variscan extension and eduction during Devonian–Carboniferous backarc extension. The reinterpretation of deep crustal zonation provides a crustal framework in which the northern limit of Avalonia corresponds to the southern limit of the deep North German Basin and the northern limit of prolific gas reservoirs and late Mesozoic inversion structures

Early Carboniferous extension in East Avalonia : 350 My record of lithospheric memory

Despite reactivations during Variscan and Alpine orogenies and the opening of the Northern Atlantic, Avalonia is one of the few regions where the initial Mid-Paleozoic basin structure is still recognisable, largely intact, and well studied. Its kinematics and dynamics remain, however, largely unknown, in particular in view of the successive late Paleozoic to recent evolution of the basin. Consequently, the importance of the mid-Palaeozoic tectonic evolution and structural controls are often overlooked and poorly understood in basin studies. In this paper, we reassess the importance of Mid-Palaeozoic tectonics on subsequent sedimentary basin evolution of north-western Europe. To this end, we analyse the dynamics of early Variscan extension in Avalonia based on the integration and re-evaluation of available geophysical and geological data from lithosphere to basin scales. Based on a revised crustal map of the Thor suture zone, we present a new paleo-tectonic reconstruction and tectonic scenario for the Devonian-Carboniferous rifting. These findings are key for a better understanding of long-lived tectonic segmentation and post-rifting deformation phases. Our findings indicate that the structural grain of many crustal fault dominated sedimentary basin structures such as the North Sea Central Graben were created in the early Carboniferous. Consequently, the main basement structuration of northwest Europe was completed before the Variscan orogeny and successive post-Variscan extension and inversion phases reactivated the existing basement structures without creating major new fault groups. Incorporation of the Paleozoic structural grain allows for a consistent tectonic framework for the Mesozoic, contributing to fundamental understanding of basin evolution. From our tectonic framework analysis, Avalonia therefore stands out as a fine example of long lived lithosphere memory, spanning over 350 My of structural control in geodynamic evolution

The Central European Permian Basins; Rheological and structural controls on basin history and on inter-basin connectivity

We analyse the relative importance of the major crustal-scale fault zones and crustal architecture in controlling basin formation, deformation and the structural connections between basins. The North and South Permian Basins of Central Europe are usually defined by the extend of Rotliegend sedimentary and volcanic units and not by a common tectonic origin or development. Instead, the sub-basins that together form the Permian Basins are each controlled by different structural and/or rheological controls that are inherited from Early Paleozoïc and older geodynamic processes, they are even located in different crustal/lithospheric domains. The North Permian basin is located on Baltic crust that was thinned during Late Proterozoïc - Early Paleozoïc times. South of the Thor suture, the South Permian basin and its sub-basins are located on Avalonian crust (Southern North Sea and North German Basins) and on the transition of East European cratonic and Avalonian crust (Polish Through). The size of crustal domains and of the faults that govern basin formation requires a regional-scale to assess their impact on basins and sub-basins. In the case of the Permian Basins this encompasses East Avalonia and surroundings, roughly speaking the area north of the Variscan Rheïc suture, east of the Atlantic and southwest of the Teisseyre-Tornquist line. This approach sheds light on the effects of long lived differences in crustal fabric which are responsible for spatial heterogeneity in stress and strain magnitudes and zonations of fracturing, burial history and temperature history. The focus on understanding the geomechanical control of large crustal-scale fault structures will provide the constraints and geometrical and compositional input for local models of stress and strain. Considering their fundamentally different structural and rheological controls, the Permian (sub)basins have a remarkably common history of subsidence and inversion, suggesting a more or less continuous link between them. Post-Variscan, Late Carboniferous-Early Permian wrench tectonics is the oldest and main identified cause for regional basin formation in Central Europe. This relatively short-lived tectonic regime cannot explain the observed common history of subsidence of the Permian Basins during the 200 My that followed. Our analysis demonstrates that transfer faults that both follow and cross rheological transitions and inherited fault zones continued to be active after the early Permian. We therefore suggests that crustal-scale transfer faults may be the missing link that explains the common subsidence history of basins with a fundamentally different crustal architecture and structural history

3D mechanical analysis of geothermal reservoir operations in faulted sedimentary aquifers using MACRIS

Abstract Accurate and efficient predictions of three-dimensional subsurface stress changes are required for the assessment of geothermal operations with respect to fault stability and the potential risk for induced seismicity. This work extends the model capabilities of Mechanical Analysis of Complex Reservoirs for Induced Seismicity (MACRIS) to account for high-resolution thermo-elastic stress evaluations in structurally complex (i.e. faulted) and matrix permeability dominated geothermal systems. By adopting a mesh-free approach suitable to industry standard flow simulation models, MACRIS is capable of preserving the complex 3D hydraulic development of the injected cold-water volume and the 3D geometrical complexities of the reservoir model. The workflow has been applied to three-dimensional models with clastic reservoir characteristics representative for low enthalpy geothermal exploitation in the Netherlands. The models are marked by a single fault, subject to no and normal offset. Comparison of simulated stress evolutions in MACRIS with alternative analytical solutions highlight the effects of stress arching involved in the poro- and thermo-elastic stress developments on complex faults intersected by or in direct contact with the cold-water volume. Results are in agreement with previous studies and show the effect of thermal stressing to be dominant, arching of stresses to occur at the rim of the cold-water volume, and in cooling reservoirs, the intersection area of the cold-water volume in direct contact with the fault plane to be the main driver for fault reactivation and subsequent seismic potential. Moreover, results show the effects of stress arching (i) to be enhanced in the case of reservoir throw and flow compartmentalization, and (ii) to be reduced by a relative increase in conductive heat transfer between the reservoir and surrounding formations