# Mission Statement

The Geothermal Energy & Geofluids group is endowed by the Werner Siemens Foundation and investigates reactive fluid (water, CO2, CxHy, N2) and (geothermal) energy (heat, pressure) transfer in the Earth’s crust employing computer simulations, laboratory experiments and field analyses to gain fundamental insights and to address a wide range of societal goals and concerns. ➞ Read More

# GEG News

22.07.2021

#### New GEG XRCT Website published

The GEG XRCT system of ETH Zurich provides resources and services in Xray-CT imaging as well as direct access to state-​of-the-art CT scanner, dedicated software, and in-situ imaging equipment.

03.06.2021

#### ETH Medal: Distinction of Doctoral Thesis – Edoardo Rossi

Dr. Edoardo Rossi received the ETH Medal (Auszeichnung von Doktorarbeit) for his doctoral thesis: “Combined Thermo-​​Mechanical Drilling Technology to Enhance Access to Deep Geo-​​Resources”.
Edoardo Rossi is currently a research associate at the Geothermal Energy and Geofluids (GEG) group and former doctoral student at GEG and the Laboratory for Transport Processes and Reactions (LTR) at D-MAVT.

20.05.2021

#### EASYGO Project granted

We want to congratulate Dr. Maren Brehme (TU Delft) with the granted ITN EASYGO ‘Efficiency & Safety in Geothermal Operations’ which creates 13 PhD positions within our network. A prestigious 3.4M€ fund has been awarded by the European Commission to her project entitled ‘EASYGO: Efficiency and Safety in Geothermal Operations’

3 out of 13 EASYGO PhD students will do their research at the GEG Group: Nicolas Rangel Jurado, Anna Kotsova and Tristan Leonar Merbecks.

30.03.2021

19.12.2020

#### 2020 MIT A+B Best Paper Award

Dr. Edoardo Rossi, research associate at the Geothermal Energy and Geofluids (GEG) group and former doctoral student at GEG and the Laboratory for Transport Processes and Reactions (LTR), and his Co-Authors received the Best Paper Award at the MIT A+B Applied Energy Symposium, held virtually at the Massachusetts Institute of Technology – MIT, with the paper:

Rossi, E., B. Adams, D. Vogler, Ph. Rudolf von Rohr, B. Kammermann, and M.O. Saar, Advanced drilling technologies to improve the economics of deep geo-resource utilization, Proceedings of Applied Energy Symposium: MIT A+B, United States, 2020 , 8, pp. 1-6, 2020. [View Abstract]Access to deep energy resources (geothermal energy, hydrocarbons) from deep reservoirs will play a fundamental role over the next decades. However, drilling of deep wells to extract deep geo-resources is extremely expensive. As a fact, drilling deep wells into hard, crystalline rocks represents a major challenge for conventional rotary drilling systems, featuring high rates of drill bit wear and requiring frequent drill bit replacements, low penetration rates and poor process efficiency. Therefore, with the aim of improving the overall economics to access deep geo-resources in hard rocks, in this work, we focus on two novel drilling methods, namely: the Combined Thermo-Mechanical Drilling (CTMD) and the Plasma-Pulse Geo-Drilling (PPGD) technologies. The goal of this research and development project is the effective reduction of the costs of drilling in general and particularly regarding accessing and using deep geothermal energy, oil or gas resources. In this work, we present these two novel drilling technologies and focus on evaluating the process efficiency and the drilling performance of these methods, compared to conventional rotary drilling.

10.12.2020

#### 2019 WRR Editors’ Choice Award

Dec. 2020: GEG paper receives a 2019 Water Resources Research Journal Editor’s Choice Award, given to 1% of papers in a given year (here 2019). The paper is:

Kittilä, A., M.R. Jalali, K.F. Evans, M. Willmann, M.O. Saar, and X.-Z. Kong, Field Comparison of DNA-Labeled Nanoparticle and Solute Tracer Transport in a Fractured Crystalline Rock, Water Resources Research, 2019.

# Videos

CO2-Plume Geothermal (CPG) power plants combine geologic CO2 storage with geothermal energy extraction.

Inexhaustible resource of clean, renewable Geothermal Energy.

By 2050, geothermal energy can cover 25% of Switzerland’s heating needs in a CO2-neutral way. © Daniel Stegmann

Grimsel rock laboratory, safer drilling methods.

# GEG Events

19.01.2022
Implementing ion exchange in Reaktoro

Svetlana Kyas (GEG group presentation)
GEG Meetings, ETH Zurich

NEXT EVENT
26.01.2022
TBA

Powei Huang (GEG group presentation)
GEG Meetings, ETH Zurich

09.02.2022
TBA

Xiang-Zhao Kong (GEG group presentation)
GEG Meetings, ETH Zurich

16.02.2022
TBA

Mohamed Ezzat (GEG group presentation)
GEG Meetings, ETH Zurich

23.03.2022
TBA

Batmagnai Erdenechimeg (GEG group presentation)
GEG Meetings, ETH Zurich

06.04.2022
TBA

Tristan Merbecks (GEG group presentation)
GEG Meetings, ETH Zurich

20.04.2022
TBA

Friedemann Samrock (GEG group presentation)
GEG Meetings, ETH Zurich

27.04.2022
TBA

Hoda Javanmard (GEG group presentation)
GEG Meetings, ETH Zurich

04.05.2022
TBA

Friedemann Samrock (GEG group presentation)
GEG Meetings, ETH Zurich

11.05.2022
TBA

Friedemann Samrock (GEG group presentation)
GEG Meetings, ETH Zurich

01.06.2022
TBA

Luise Dambly (GEG group presentation)
GEG Meetings, ETH Zurich

08.06.2022
TBA

Serhat Kucuk (GEG group presentation)
GEG Meetings, ETH Zurich

15.06.2022
TBA

Kevin Hau (GEG group presentation)
GEG Meetings, ETH Zurich

22.06.2022
TBA

Allan Leal (GEG group presentation)
GEG Meetings, ETH Zurich

29.06.2022
TBA

Isamu Naets (GEG group presentation)
GEG Meetings, ETH Zurich

##### Refereed journal papers accepted the last 6 months

Underlined names are links to current or past GEG members

On the applicability of connectivity metrics to rough fractures under normal stress
Javanmard, H, M. O. Saar, and D. Vogler, Advances in Water Resources, (in press). [View Abstract]Rough rock fractures have complex geometries which result in highly heterogeneous aperture fields. To accurately estimate the permeability of such fractures, heterogeneity of the aperture fields must be quantified. In this study heterogeneity of single rough rock fractures is for the first time parametrized by connectivity metrics, which quantify how connected the bounds of a heterogeneous field are. We use 3000 individual realizations of synthetic aperture fields with different statistical parameters and compute three connectivity metrics based on percolation theory for each realization. The sensitivity of the connectivity metrics with respect to the determining parameter, i.e the cutoff threshold, is studied and the correlation between permeability of the fractures and the computed connectivity metrics is presented. The results show that the $\Theta$ connectivity metric predicts the permeability with higher accuracy. All three studied connectivity metrics provide better permeability estimations when a larger aperture value is chosen as the cutoff threshold. Overall, this study elucidates that using connectivity metrics provides a less expensive alternative to fluid flow simulations when an estimation of fracture permeability is desired. (Paper accepted 2022-01-07)
Techno-economic analysis of Advanced Geothermal Systems (AGS)
Malek, A.E., B.M. Adams, E. Rossi, H.O. Schiegg, and M.O. Saar, Renewable Energy, 2022. [View Abstract]Advanced Geothermal Systems (AGS) generate electric power through a closed-loop circuit, after a working fluid extracts thermal energy from rocks at great depths via conductive heat transfer from the geologic formation to the working fluid through an impermeable wellbore wall. The slow conductive heat transfer rate present in AGS, compared to heat advection, makes AGS uneconomical to this date. To investigate what would be required to render AGS economical, we numerically model an example AGS using the genGEO simulator to obtain its electric power generation and its specific capital cost. Our numerical results show that using CO2 as the working fluid benefits AGS performance. Additionally, we find that there exists a working fluid mass flowrate, a lateral well length, and a wellbore diameter which minimize AGS costs. However, our results also show that AGS remain uneconomical with current, standard drilling technologies. Therefore, significant advancements in drilling technologies, that have the potential to reduce drilling costs by over 50%, are required to enable cost-competitive AGS implementations. Despite these challenges, the economic viability and societal acceptance potential of AGS are significantly raised when considering that negative externalities and their costs, so common for most other power plants, are practically non-existent with AGS. (Paper accepted 2022-01-04)
Numerical Modeling of the Effects of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling
Ezzat, M., B. M. Adams, M.O. Saar, and D. Vogler, Energies, 15/1, 2022. [View Abstract]Drilling costs can be 80% of geothermal project investment, so decreasing these deep drilling costs substantially reduces overall project costs, contributing to less expensive geothermal electricity or heat generation. Plasma Pulse Geo Drilling (PPGD) is a contactless drilling technique that uses high-voltage pulses to fracture the rock without mechanical abrasion, which may reduce drilling costs by up to 90% of conventional mechanical rotary drilling costs. However, further development of PPGD requires a better understanding of the underlying fundamental physics, specifically the dielectric breakdown of rocks with pore fluids subjected to high-voltage pulses. This paper presents a numerical model to investigate the effects of the pore characteristics (i.e., pore fluid, shape, size, and pressure) on the occurrence of the local electric breakdown (i.e., plasma formation in the pore fluid) inside the granite pores and thus on PPGD efficiency. Investigated are: (i) two pore fluids, consisting of air (gas) or liquid water; (ii) three pore shapes, i.e., ellipses, circles, and squares; (iii) pore sizes ranging from 10 to 150 μm; (iv) pore pressures ranging from 0.1 to 2.5 MPa. The study shows how the investigated pore characteristics affect the local electric breakdown and, consequently, the PPGD process. (Paper accepted 2021-12-30)
Accelerated reactive transport simulations in heterogeneous porous media using Reaktoro and Firedrake
Kyas, S., D. Volpatto, M. O. Saar, and A. Leal, Computational Geosciences, (in press). [View Abstract]This work investigates the performance of the on-demand machine learning (ODML) algorithm introduced in Leal et al. (2020) when applied to different reactive transport problems in heterogeneous porous media. This approach was devised to accelerate the computationally expensive geochemical reaction calculations in reactive transport simulations. We demonstrate that even with strong heterogeneity present, the ODML algorithm speeds up these calculations by one to three orders of magnitude. Such acceleration, in turn, significantly advances the entire reactive transport simulation. The performed numerical experiments are enabled by the novel coupling of two open-source software packages: Reaktoro (Leal, 2015) and Firedrake (Rathgeber et al., 2016). The first library provides the most recent version of the ODML approach for the chemical equilibrium calculations, whereas, the second framework includes the newly implemented conservative Discontinuous Galerkin finite element scheme for the Darcy problem, i.e., the Stabilized Dual Hybrid Mixed (SDHM) method (Núñez et al., 2012). (Paper accepted 2021-12-12)
Flexible CO2-Plume Geothermal (CPG-F): Using Geologically Stored CO2 to Provide Dispatchable Power and Energy Storage
Fleming, M.R., B.M. Adams, J.D. Ogland-Hand, J.M. Bielicki, T.H. Kuehn, and M.O. Saar, Energy Conversion and Management, 253/115082, 2022. [View Abstract]CO2-Plume Geothermal (CPG) power plants can use geologically stored CO2 to generate electricity. In this study, a Flexible CO2 Plume Geothermal (CPG-F) facility is introduced, which can use geologically stored CO2 to provide dispatchable power, energy storage, or both dispatchable power and energy storage simultaneously—providing baseload power with dispatchable storage for demand response. It is found that a CPG-F facility can deliver more power than a CPG power plant, but with less daily energy production. For example, the CPG-F facility produces 7.2 MWe for 8 hours (8h-16h duty cycle), which is 190% greater than power supplied from a CPG power plant, but the daily energy decreased by 61% from 60 MWe-h to 23 MWe-h. A CPG-F facility, designed for varying durations of energy storage, has a 70% higher capital cost than a CPG power plant, but costs 4% to 27% more than most CPG-F facilities, designed for a specific duration, while producing 90% to 310% more power than a CPG power plant. A CPG-F facility, designed to switch from providing 100% dispatchable power to 100% energy storage, only costs 3% more than a CPG-F facility, designed only for energy storage. (Paper accepted 2021-11-28)
Numerical analysis and optimization of the performance of CO2-Plume Geothermal (CPG) production wells and implications for electric power generation
Ezekiel, J., B.M. Adams, M.O. Saar, and A. Ebigbo, Geothermics, 98/102270, 2022. [View Abstract]CO2-Plume Geothermal (CPG) power plants can produce heat and/or electric power. One of the most important parameters for the design of a CPG system is the CO2 mass flowrate. Firstly, the flowrate determines the power generated. Secondly, the flowrate has a significant effect on the fluid pressure drawdown in the geologic reservoir at the production well inlet. This pressure drawdown is important because it can lead to water flow in the reservoir towards and into the borehole. Thirdly, the CO2 flowrate directly affects the two-phase (CO2 and water) flow regime within the production well. An annular flow regime, dominated by the flow of the CO2 phase in the well, is favorable to increase CPG efficiency. Thus, flowrate optimizations of CPG systems need to honor all of the above processes. We investigate the effects of various operational parameters (maximum flowrate, ad- missible reservoir-pressure drawdown, borehole diameter) and reservoir parameters (permeability anisotropy and relative permeability curves) on the CO2 and water flow regime in the production well and on the power generation of a CPG system. We use a numerical modeling approach that couples the reservoir processes with the well and power plant systems. Our results show that water accumulation in the CPG vertical production well can occur. However, with proper CPG system design, it is possible to prevent such water accumulation in the pro- duction well and to maximize CPG electric power output. (Paper accepted 2021-10-06)
Multi-disciplinary characterizations of the Bedretto Lab - a unique underground geoscience research facility
Ma, X., M. Hertrich, et. al, F. Amann, V. Gischig, T. Driesner, S. Löw, H. Maurer, M.O. Saar, S. Wiemer, and D. Giardini, Solid Earth, 2021. [View Abstract]Xiaodong Ma1, Marian Hertrich1, Kai Bröker1, Nima Gholizadeh Doonechaly1, Rebecca Hochreutener1, Philipp Kästli1, Hannes Krietsch3, Michèle Marti1, Barbara Nägeli1, Morteza Nejati1, Anne Obermann21, Katrin Plenkers1, Alexis Shakas1, Linus Villiger1, Quinn Wenning1, Alba Zappone1, Falko Bethmann2, Raymi Castilla2, Francisco Seberto2, Peter Meier2, Florian Amann3, Valentin Gischig4, Thomas Driesner1, Simon Löw1, Hansruedi Maurer1, Martin O. Saar1, Stefan Wiemer1, Domenico Giardini1 1Department of Earth Sciences, ETH Zürich, Zürich, 8092, Switzerland 2 Swiss Seismological Service, ETH Zurich, Zürich, 8092, Switzerland 2Geo-Energie Suisse, AG, Zürich, 8004, Switzerland 3Engineering Geology and Hydrogeology, RWTH Aachen, Aachen, 52062, Germany 4CSD Ingenieure AG, Liebefeld, 3097, Switzerland Correspondence to: Xiaodong Ma (xiaodong.ma@erdw.ethz.ch) (Paper accepted 2021-12-17)
Sensitivity of Reservoir and Operational Parameters on the Energy Extraction Performance of Combined CO2-EGR–CPG Systems
Ezekiel, J., D. Kumbhat, A. Ebigbo, B.M. Adams, and M.O. Saar, Energies, 14/6122, 2021. [View Abstract]There is a potential for synergy effects in utilizing CO2 for both enhanced gas recovery (EGR) and geothermal energy extraction (CO2-plume geothermal, CPG) from natural gas reservoirs. In this study, we carried out reservoir simulations using TOUGH2 to evaluate the sensitivity of natural gas recovery, pressure buildup, and geothermal power generation performance of the combined CO2-EGR–CPG system to key reservoir and operational parameters. The reservoir parameters included horizontal permeability, permeability anisotropy, reservoir temperature, and pore-size- distribution index; while the operational parameters included wellbore diameter and ambient surface temperature. Using an example of a natural gas reservoir model, we also investigated the effects of different strategies of transitioning from the CO2-EGR stage to the CPG stage on the energy-recovery performance metrics and on the two-phase fluid-flow regime in the production well. The simulation results showed that overlapping the CO2-EGR and CPG stages, and having a relatively brief period of CO2 injection, but no production (which we called the CO2-plume establishment stage) achieved the best overall energy (natural gas and geothermal) recovery performance. Permeability anisotropy and reservoir temperature were the parameters that the natural gas recovery performance of the combined system was most sensitive to. The geothermal power generation performance was most sensitive to the reservoir temperature and the production wellbore diameter. The results of this study pave the way for future CPG-based geothermal power-generation optimization studies. For a CO2-EGR–CPG project, the results can be a guide in terms of the required accuracy of the reservoir parameters during exploration and data acquisition. (Paper accepted 2021-09-22)
Connecting Dynamic Heat Demands of Buildings with Borehole Heat Exchanger Simulations for Realistic Monitoring and Forecast
Niederau, J., J. Fink, and M. Lauster, Advances in Geosciences, 56, pp. 45-56, 2021. [View Abstract]Space heating is a major contributor to the average energy consumption of private households, where the energy standard of a building is a controlling parameter for its heating energy demand. Vertical Ground Source Heat Pumps (vGSHP) present one possibility for a low-emission heating solution. In this paper, we present results of building performance simulations (BPS) coupled with vGSHP simulations for modelling the response of vGSHP-fields to varying heating power demands, i.e. different building types. Based on multi-year outdoor temperature data, our simulation results show that the cooling effect of the vGSHPs in the subsurface is about 2 K lower for retrofitted buildings. Further, a layout with one borehole heat exchanger per building can be efficiently operated over a time frame of 15 years, even if the vGSHP-field layout is parallel to regional groundwater flow in the reservoir body. Due to northward groundwater flow, thermal plumes of reduced temperatures develop at each vGSHP, showing that vGSHPs in the southern part of the model affect their northern neighbors. Considering groundwater flow in designing the layout of the vGSHP-field is conclusively important. Combining realistic estimates of the energy demand of buildings by BPS with subsurface reservoir simulations thus presents a tool for monitoring and managing the temperature field of the subsurface, affected by Borehole Heat Exchanger (BHE) installations. (Paper accepted 2021-09-16)
Simulating Plasma Formation in Pores under Short Electric Pulses for Plasma Pulse Geo Drilling (PPGD)
Ezzat, M., D. Vogler, M. O. Saar, and B. M. Adams, Energies, 14/16, 2021. [View Abstract]

Plasma Pulse Geo Drilling (PPGD) is a contact-less drilling technique, where an electric discharge across a rock sample causes the rock to fracture. Experimental results have shown PPGD drilling operations are successful if certain electrode spacings, pulse voltages, and pulse rise times are given. However, the underlying physics of the electric breakdown within the rock, which cause damage in the process, are still poorly understood.

This study presents a novel methodology to numerically study plasma generation for electric pulses between 200 to 500 kV in rock pores with a width between 10 and 100 $\mu$m. We further investigate whether the pressure increase, induced by the plasma generation, is sufficient to cause rock fracturing, which is indicative of the onset of drilling success.

We find that rock fracturing occurs in simulations with a 100 $\mu$m. pore size and an imposed pulse voltage of approximately 400 kV. Furthermore, pulses with voltages lower than 400 kV induce damage near the electrodes, which expands from pulse to pulse, and eventually, rock fracturing occurs. Additionally, we find that the likelihood for fracturing increases with increasing pore voltage drop, which increases with pore size, electric pulse voltage, and rock effective relative permittivity while being inversely proportional to the rock porosity and pulse rise time.

(Paper accepted 2021-07-29)