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Side Event Thermo-Hydro-Mechanical Modeling (THM) and Ground Truth II (in English)
Modeling geothermal reservoirs needs a lot of experience and a lot of parameters to give reliable results. It is often seen by reality, that the models are not describing exactly the behavior of the reservoir. What are the reasons for these discrepancies between simulation and real operation?
Of utmost importance for a reliable THM modelling are parameters from borehole and surface measurements, such as:
‐ Geometrical input
‐ Geological input
‐ Initial temperatures
‐ Petrophysical parameters
‐ Fluids, dissolved solids, not condensable gases
‐ Fault estimates, size, parameters, orientation
‐ Initial stress field, stress field development
‐ Pore pressure
‐ Temperature development
‐ Borehole fault intersection
‐ Internal (reservoir) erosion
Further issue are:
‐ Machine learning
‐ Extraction and injection
‐ Modelling, Software,
‐ Mathematical issues, codes, commercial software, computer capacity/ time
‐ Reservoir scales
‐ Parameters, rock, fluids
‐ Validation by logging
‐ Validation by pumping tests
‐ History matching, case histories, lessons learned
‐ Induced seismicity, seismic catalogue, max. magnitudes
‐ Thermal breakthrough
‐ Reservoir sustainability (50y)
The workshop will be a cross-over event between the O&G and the geothermal community.
|Zusammenfassung der Sitzung|
Modelling geothermal reservoirs needs a lot of experience and a lot of parameters to give reliable results. It is often seen by reality, that the models are not describing exactly the behavior of the reservoir. What are the reasons for these discrepancies between simulation and real operation?
13:00 - 13:30
The hydraulic effect of fault zones in relation to deep hydro-geothermal energy exploration in the Upper Jurassic aquifer of Southern Germany
Technische Universität München, Deutschland
Fault zones in the Upper Jurassic aquifer (UJA) of the North Alpine Foreland Basin are generally regions with possibly increased hydraulic properties. They are consequently often part of the geothermal exploration in this area and targets for drilling operation. Data from this aquifer, gathered in pump tests, however shows that only four out of 44 successful wells exhibit hydraulic proof for the presence of such a fault zone in terms of a bi-/linear flow regime. Besides technical effects, also the contrast in hydraulic properties itself, between fault zone and surrounding host rock, can prevent the detection of a fault zone in pump test data. This means a certain threshold has to be surpassed until its effects become clearly visible. With this uncertainty in the detection of fault zones in pressure data goes along the question regarding their share in well productivity. Especially relevant is this question with a focus on hydraulically active fault zones that remain undetected in a pumping test (hydraulically hidden fault zones).
A simplified realistic numerical model was constructed and calibrated with pressure data from an exploration site in the south of Munich. In a first step, this model was used to observe the presence of linear and bilinear flow in dependence of the UJA parameter space. Sampling the possible hydraulic property-combinations with the help of an HPC (high performance computing) cluster and automating the detection of the corresponding main flow type allowed to quantify the areas in parameter space where the fault zone-related flow regimes of interest are present. Through the investigation of more than 30000 combinations between fault zone permeability, matrix permeability, fault zone storage, matrix storage and fault zone thickness, it was found that, in the parameter space of the UJA, a bilinear flow can be observed for the first time only if the matrix permeability is lower than 2.0 x 10-13 m², and a linear flow for matrix permeability values below 6.0 x 10-14 m². Additionally, it was shown that fault zones, which have better hydraulic properties than the surrounding matrix, can indeed be hidden in pumping tests due to the parameter setting.
With this knowledge of flow regimes transitions in the parameter space of the UJA, a further investigation was carried out by enhancing the calibrated numerical model through application of the Reduced Basis method. This enabled a quantification of the effect of hydraulically active fault zones on the well-productivity-index (PI) in dependency of the UJA parameter space based on more than six million simulations. Further, it was possible to investigate spatially the distribution of flow regimes in the greater area of Munich depending on different fault zone types and their influence on the PI. An additional 81 million simulations based on maps of the hydraulic properties of the UJA were therefor deployed. The results of this secondary investigation suggest that hydraulically hidden fault zones can increase the PI significantly. The comparison with flow regime observations of geothermal wells in the greater area of Munich suggests that a hydraulically active fault zone thickness of ≥ 100 m is unlikely for the UJA. Consequences of these spatial findings were further used as part of the success-forecast for geothermal wells in the “Geothermie Masterplan” of the Land of Bavaria.
Finally, an open source Python tool (“uja_faultzones” https://github.com/Florian-Konrad/uja_faultzones) was developed that efficiently incorporates the numerical models and the methodology to derive flow regime and well productivity influence for an arbitrary fault zone type. Its fast calculation times of ~0.4s per simulation on a standard workstation enable reservoir engineers to quickly simulate a multitude of pumping tests of different fault zone realizations and derive their hydraulic influence.
14:00 - 14:30
THM modeling of former hydrocarbon reservoirs for high-temperature heat storage
Karlsruhe Institute of Technology, Deutschland
More than 50% of German CO2 emissions are related to the supply of heat for buildings and processes. Due to seasonal fluctuations in demand, especially for heating buildings, the possibility of locally storing excess heat in summer, which can be extracted from storage in winter, is becoming increasingly important. With the current state of technology and foreseeable developments, significant amounts of heat can only be stored underground, taking advantage of the large storage volumes available. In contrast to storage in near-surface aquifers (ATES: Aquifer Thermal Energy Storage), much higher thermal energies can be stored in deep heat reservoirs due to the significantly higher injection temperatures.
Based on generic thermal-hydraulic modeling, a previous study showed the overall high potential of former hydrocarbon reservoirs in the Upper Rhine Graben for high-temperature heat storage. However, for a more complete assessment of the potential, all coupled physical processes must be considered. Using the DeepStor case study, a pilot project on the Campus North of the Karlsruhe Institute of Technology, the present study addresses the coupled thermal-hydraulic-mechanical processes and their influence on the realization of high-temperature heat storage systems. In particular, we consider the influence of cyclic changes of pore and thermoelastic stresses on uplift at the surface.
14:30 - 15:00
Challenges in geothermal reservoir modeling: from applications to future opportunities
Karlsruher Institut für Technologie, Deutschland
The physical processes and their mutual interactions within a geothermal reservoir are highly complex and unique, and can differ significantly from place to place. As a result, each model presents its own challenges. Critical aspects include the identification and integration of relevant geological structures and fluid pathways, appropriate choice of boundary conditions, calibration by means of existing field investigations and also operational management. In this presentation we would like to show the possibilities and challenges of modeling geothermal reservoirs. For this purpose, we present both synthetic and real thermo-hydraulic-mechanical models of different types of geothermal reservoirs and discuss their results.
The geothermal power plant in Soultz-sous-Forêts represents a pioneer for economic use Enhanced geothermal systems (EGS). More than 20 years of research have created a unique database of experimental data that can be used nowadays to calibrate thermo-hydraulic models of the complex fault and fracture network at Soultz and to predict a future sustainable operation. The aquifers of the Upper Rhine Valley or the upper Jurassic in the greater Munich area pose a quite different challenge. Here, the combination of matrix permeability, faulted (and in limestones karstified) leads to a vast sensitivity regarding the internal geology, but also partly high flow rates. We present initial results of calibrated thermal-hydraulic-mechanical models of a continuous long-term operation to track changes in the long-term behavior of the reservoir. Finally, we will show how kilometer-scale hydrothermal convection cells can explain thermal anomalies in faulted sandstone reservoirs located in northwestern Germany.
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