Conference Agenda

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Session Overview
EGW - Assessment of Geothermal Resources
Thursday, 23/Sept/2021:
9:30am - 10:45am

9:30am - 9:42am

3D Basin modelling of the northern Upper Rhine Graben : insights on geothermal fluid pathways

Gillian BETHUNE1, Adriana LEMGRUBER-TRABY2, Claire BOSSENNEC3, Kristian BÄR3, Jeroen VAN DER VAART3, Christine SOUQUE2, Renaud DIVIES2

1IFP Energies Nouvelles, France - UniLaSalle Beauvais/ Université de Cergy Pontoise; 2IFP Energies Nouvelles, France; 3Geothermal Science and Technology, Institute of Applied Geosciences, Technical University, Darmstadt (Germany)

The area of the Upper Rhine Graben (URG) is known for its geothermal potential. However, the recent interest for lithium co-production from geothermal brines raises questions about the quantification and dynamics of fluid flow paths in the geothermal system at the basin scale. This study aims to better understand the impact of the fluid circulation on the temperature field evolution and on the fluid recharge by performing a 3D thermal basin modeling.

The Buntsandstein group sandstones, constituted by early Triassic fluvial to playa-lake deposits are one of the targeted reservoir layers for geothermal and lithium co-production. They overlay permo-carboniferous deposits and the the crystalline variscan basement. The basement inherited structural network plays an important role on heat distribution and flow pathways on the graben shoulders and within the basement. Faults control also the lateral and vertical reservoir connections and fluid mixing, and thus need to be integrated into the burial model.

In this study, the focus is made on the northern part of the URG between the cities of Haguenau (France) and Frankfurt (Germany). A new structural model and the geometry of twelve sedimentary layers are implemented in TemisFlow® software. The thermal simulation included both conductive and advective heat transfer. The model integrates the Tertiary rift event from 46 Ma to 23 Ma, by coupling the lithosphere with the depositional evolution. The influence of permeability heterogeneity in the crystalline basement, the role of the main graben border faults, and some selected internal faults on the fluid flow were also investigated. The model is calibrated with the available temperature measurement data, vitrinite reflectance data and temperature maps at different depths or horizons.

As a result, the simulations show that the thermal structure of the Eastern part of the URG is mainly controlled by conductive heat transfer, and directly related to the burial. Modeling outputs also highlight the impact of the basement heterogeneity on hydrothermal circulation and the temperature field of the Western part of the URG.

9:42am - 9:54am

An assessment of geothermal energy potential for power generation in Iran

Mirmahdi Seyedrahimi-Niaraq1, Reza Taherdangkoo2, Faramarz Doulati Ardejani3

1University of Mohaghegh Ardabili, Iran, Islamic Republic of; 2Institute of Geotechnics, Germany; 3University of Tehran, Iran, Islamic Republic of

Energy generated from geothermal systems is a good alternative to non-renewable fossil fuels and plays an important role in reducing greenhouse gas emissions. Geothermal energy is generated from the inner parts of the earth as tangible heat. The geothermal energy is distributed between the host rock and the natural fluid contained in fractures and pore spaces of the rocks in the earth's crust. Suitable areas for the exploitation of geothermal energy are related to tectonic activities and hot spots of the earth, which have signs of surface activities such as hot springs, geysers and volcanic rocks. Iran, under the influence of these tectonic and volcanic activities, has large sources of geothermal energy. A geothermal power plant with a capacity of 5 MWe is being built in the Meshkinshahr volcanic zone in the northwest Iran. This research aims to evaluate these resources for electricity generation by studying the available data obtained from the surface and subsurface exploration activities for the entire country. The results of exploratory studies in five provinces of Iran have led to introduction of 35 potential geothermal areas. Among them, the subsurface data of the northwest of Sabalan reveals that this area has a potential electricity generation capacity of about 50 MW. Further investigations and investments are required in particular in the zones where there exist high-temperature hot springs. Therefore, the capacity of electricity generation in this field would be significantly increased.

9:54am - 10:06am

Impacts of probabilistic geological realizations in a geothermal reservoir using numerical and statistical investigations

Ali Dashti1, Maziar Gholami Korzani1, Christophe Geuzaine2, Thomas Kohl1

1Institute of Applied Geosciences, Karlsruhe Institute of Technology, Adenauerring 20b, 76131 Karlsruhe, Germany; 2Université de Liège, Institut Montefiore B28, 4000 Liège, Belgium

Achieving a (?) reliable geological model is the foremost step in all underground resource assessments. However, regarding the sparsity of data and lack of knowledge, a spectrum of solutions makes more sense compared to a single deterministic model. It this study, a probabilistic geological modeler (Gempy) is used to understand the effect of existing uncertainty in the data representing subsurface layers and faults. A synthetic single fault model in which both the layers and fault are perturbed is designed. Random numbers are used for perturbation to prevent from any bias. In the first round of uncertainty analysis, thickness of reservoir layer in the footwall and location of the faults are perturbed. In the next round, dip and direction of fault are considered to be uncertain. In each of two rounds, 20 geological realization are resulted to act as a framework for later numerical simulations. After perturbing different elements of the synthetic geological setting and generating mesh (using GMSH) for each scenario (40 ones), TIGER code is exerted to simulate the tracer flow path. All the three packages are open source and availability of Gempy and GMSH in Python ecosystem facilitates the transfer from structural models to a high quality mesh. A doublet system (one injection and one production well) penetrating a geothermal reservoir is simulated in this study. In the base model, only the production well is passing through the fault but adding uncertainty to location of the fault resulted in having realization in which both wells penetrate the fault. Through simulating the tracer path for all geological realizations, sensitivity of results to the location of the fault is clearly observed. Statistical analyses revealed and numerically quantified the effect of structural uncertainty on the flow properties of a doublet system in a geothermal reservoir.

10:06am - 10:18am

A Heat Demand Map of North-West Europe - its impact on supply areas and identification of potential production areas for deep geothermal energy

Eileen Herbst1,2, Elias Khashfe1,2, Alexander Jüstel1,2, Frank Strozyk2, Peter Kukla1,2

1Geological Institute, RWTH Aachen University; 2Fraunhofer Research Institution for Energy Infrastructures and Geothermal Systems IEG, Germany

To achieve the Paris Agreement's goal of maximum global warming by 2 degrees, CO2 reduction is indispensable. Space heating for residential, service and industrial buildings amounts to 26% of EU's final energy consumption with about 3347 TWh/a. Approximately 75% of the heat produced is generated by fossil fuels with high CO2 emissions. Those Emissions can be reduced by implementation of renewable energy sources, such as deep geothermal energy.

As Part of the Interreg NWE project “DGE-ROLLOUT - Roll-out of Deep Geothermal Energy in NWE” a heat demand map of North-West Europe is developed to determine the spatial heat demand distribution of residential, service and industrial buildings. Subsequently limiting factors including subsurface geology and energy infrastructures are used to identify potential production areas for deep geothermal energy. In addition, potential supply areas of deep geothermal power plants by given annual heat production are estimated. The results will show that there is a great potential for CO2 reduction through the use of deep geothermal energy, especially in densely populated and heat consuming areas.

10:18am - 10:30am

The permeability of granite deformed in the brittle regime to large strains: Implications for the permeability of fractured geothermal reservoirs

Michael Heap1,2, Hugo Duwiquet3,4, Luke Griffiths5, Laurent Guillou-Frottier3,4, Patrick Baud1, Marie Violay6

1ITES, Strasbourg, France; 2IUF, Paris, France; 3ISTO, Université d'Orléans, France; 4BRGM, France; 5NGI, Oslo, Norway; 6EPFL, Lausanne, Switzerland

Efficient fluid flow and circulation are important for an economically viable geothermal reservoir. One type of underexplored reservoir for high-temperature geothermal exploitation is a crustal fault zone, where hot fluids from depths corresponding to the brittle-ductile transition are brought to the surface via crustal-scale, permeable fault zones. To better understand the evolving permeability of reservoir rock during deformation in the brittle regime—fault formation and sliding on the fault—we performed triaxial experiments on samples of well-characterised Lanhélin granite (France) in which we measured the permeability of the sample during deformation to large strains (up to an axial strain of about 0.1). We first thermally-stressed our samples to 700 °C to ensure their permeability was sufficiently high to measure on reasonable laboratory timescales. Experiments were performed on water-saturated samples (pore fluid pressure = 10 MPa), at effective pressures of 10, 30, and 50 MPa (corresponding to a maximum depth of about 3 km), and at ambient laboratory temperatures. Our data show that sample permeability decreased (by about an order of magnitude) prior to macroscopic shear failure, as the closure of pre-existing microcracks outweighed the formation of new microcracks during loading up to the peak stress. Sample permeability increased following fracture formation (by about a factor of two). Sliding on the fracture to large strains (corresponding to a fault displacement of ~7 mm) did not appreciably change the permeability of the sample, and therefore the permeability of the fracture did not fall below that of the host-rock. Although the permeability of the sample at the frictional sliding stress was lower at a higher effective pressure (by about an order of magnitude between 10 and 50 MPa), the evolution of sample permeability was qualitatively similar for effective pressures of 10−50 MPa. We now plan to use the results of this experimental study to inform numerical modelling designed to explore the influence of macroscopic fractures on fluid flow within a fractured geothermal reservoir.