# 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.

# GEG News

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.

02.11.2020

On Friday, October 30th, Mehrdad Ahkami has successfully defended his PhD thesis, entitled: “Experimental and numerical study of fluid flow, solute transport, and mineral precipitation in fractured porous media”.

09.09.2020

#### Doctoral Examination Marina Grimm Lima

On Tuesday, September 8th, Marina Grimm Lima has successfully defended her PhD thesis, entitled: “Evolution of permeability of natural fractures due to THMC processes in the context of CO2-based reservoir applications”.

20.08.2020

#### Airborne geomagnetic survey over the lavafields near Þorbjörn volcano in Iceland

Franco Aubert and Friedemann Samrock just completed 137km of airborne geomagnetic survey over the lavafields near Þorbjörn volcano in Iceland. The study is part of project MAGIC – Multidisciplinary imaging and characterization of the magma/fluid reservoir beneath Svartsengi – in collaboration with GFZ Potsdam, ISOR and the University of Iceland. The photo shows our drone during a mission and the 74.4MWe Svartsengi power plant in the background. (click on picture to enlarge)

09.08.2020

#### Tenure for Dr. Xiang-Zhao Kong

Dr. Xiang-Zhao Kong has achieved permanency status (tenure) in the Geothermal Energy and Geofluids (GEG) group of the Department of Earth Sciences at ETH Zurich. He has done an outstanding job, which includes research and publications, student supervision, raising grants, and setting up the GREAT Visualization lab of the GEG Group.

06.08.2020

#### New project: studying geothermal resources in Ethiopia

New project MIRIGE in Ethiopia to study magmatic rifting and the formation of geothermal resources funded by ETH grant.

28.07.2020

#### Doctoral Examination Justin Ezekiel

On Monday, July 27th, Justin Ezekiel has successfully defended his PhD thesis, entitled: “Assessment and optimization of geological carbon storage and energy production from deep natural gas reservoirs”.

17.06.2020

#### Top Ranking for ETH Zurich in the QS World University Ranking

ETH Zurich has demonstrated continuous improvement in the QS World University Ranking, from 12th place in 2015 to 6th place in last year’s 2020 ranking.

#### Top 1 Ranking for ETH Zurich’s Earth Sciences in QS World University Rankings

Earth and marine sciences at ETH Zurich was ranked the best in the world for the 5th time in a row.

29.05.2020

#### Doctoral Examination Jin Ma

On Thursday, May 28th, Jin Ma has successfully defended her PhD thesis, entitled: “Investigation of mineral reactivity in CO2-bearing solutions: An application to CCUS in geothermal reservoirs”.

27.03.2020

#### Doctoral Examination Mahmoud Hefny

On Thursday, March 26th, Mahmoud Hefny has successfully defended his PhD thesis, entitled: “Rock physics and heterogeneities characterization controlling fluid flow in reservoir rocks”.

25.03.2020

#### Doctoral Examination Philipp Schädle

On Tuesday, March 24th, Philipp Schädle has successfully defended his PhD thesis, entitled: “Flow and transport through fractured rock – numerical approaches to account for fracture heterogeneity”.

# GEG Videos

Inexhaustible resource of clean, renewable Geothermal Energy.

Grimsel rock lab, feasibility of geothermal power plants.

Grimsel rock laboratory, safer drilling methods.

A short video about ETH Zurich

# GEG Events

NEXT EVENT
20.01.2021
Interaction between turbulence and stratification in atmospheres: penetrative convection, internal gravity waves and large-scale flows

Pierre Léard (GEG group presentation)
GEG Meetings, ETH Zurich

03.02.2021
TBA

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

10.02.2021
TBA

Jan Niederau (GEG group presentation)
GEG Meetings, ETH Zurich

17.02.2021
TBA

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

24.02.2021
TBA

Mahmoud Hefny (GEG group presentation)
GEG Meetings, ETH Zurich

Quantification of mineral accessible surface area and flow-dependent fluid-mineral reactivity at the pore scale
Ma, J., M. Ahkami, M.O. Saar, and X.-Z. Kong, Chemical Geology, (in press). [View Abstract]Accessible surface areas (ASAs) of individual rock-forming minerals exert a fundamental control on the maximum mineral reactivity with formation fluids. Notably, ASA efficiency during fluid-rock reactions can vary by orders of magnitude, depending on the inflow fluid chemistry and the velocity field. Due to the lack of adequate quantification methods, determining the mineral-specific ASAs and their reaction efficiency still remain extremely difficult. Here, we first present a novel joint method that appropriately calculates ASAs of individual minerals in a multi-mineral sandstone. This joint method combines SEM-image processing results and Brunauer-Emmett-Teller (BET) surface area measurements by a Monte-Carlo algorithm to derive scaling factors and ASAs for individual minerals at the resolution of BET measurements. Using these atomic-scale ASAs, we then investigate the impact of flow rate on the ASA efficiency in mineral dissolution reactions during the injection of CO2-enriched brine. This is done by conducting a series of pore-scale reactive transport simulations, using a two-dimensional (2D) scanning electron microscopy (SEM) image of this sandstone. The ASA efficiency is determined employing a domain-averaged dissolution rate and the effective surface area of the most reactive phase in the sandstone (dolomite). As expected, the dolomite reactivity is found to increase with the flow rate, due to the on average high fluid reactivity. The surface efficiency increases slightly with the fluid flow rate, and reaches a relatively stable value of about 1%. The domain averaged method is then compared with the in-out averaged method (i.e the “Black-box” approach), which is often used to analyzed the experimental observations. The in-out averaged method yields a considerable overestimation of the fluid reactivity, a small underestimation of the dolomite reactivity, and a considerable underestimation of the ASA efficiency. The discrepancy between the two methods is becoming smaller when the injection rate increases. Our comparison suggests that the result interpretation of the in-out averaged method should be contemplated, in particular, when the flow rate is small. Nonetheless, our proposed ASA determination method should facilitate accurate calculations of fluid-mineral reactivity in large-scale reactive transport simulations, and we advise that an upscaling of the ASA efficiency needs to be carefully considered, due to the low surface efficiency.
Verification benchmarks for single-phase flow in three-dimensional fractured porous media
Berre, I., W. M. Boon, B. Flemisch, A. Fumagalli, D. Gläser, E. Keilegavlen, A. Scotti, I. Stefansson, et al., P. Schädle, and et al., Advances in Water Resources, 147, pp. 103759, 2021. [View Abstract]Flow in fractured porous media occurs in the earth’s subsurface, in biological tissues, and in man-made materials. Fractures have a dominating influence on flow processes, and the last decade has seen an extensive development of models and numerical methods that explicitly account for their presence. To support these developments, we present a portfolio of four benchmark cases for single-phase flow in three-dimensional fractured porous media. The cases are specifically designed to test the methods’ capabilities in handling various complexities common to the geometrical structures of fracture networks. Based on an open call for participation, results obtained with 17 numerical methods were collected. This paper presents the underlying mathematical model, an overview of the features of the participating numerical methods, and their performance in solving the benchmark cases.
The Value of CO2-Bulk Energy Storage with Wind in Transmission-Constrained Electricity Systems
Ogland-Hand, J., J. Bielicki, B. Adams, E. Nelson, T. Buscheck, M.O. Saar, and R. Sioshansi, Energy Conversion and Management, 2021. [View Abstract]High-voltage direct current (HVDC) transmission infrastructure can transmit electricity from regions with high-quality variable wind and solar resources to those with high electricity demand. In these situations, bulk energy storage (BES) could beneficially increase the utilization of HVDC transmission capacity. Here, we investigate that benefit for an emerging BES approach that uses geologically stored CO2 and sedimentary basin geothermal resources to time-shift variable electricity production. For a realistic case study of a 1 GW wind farm in Eastern Wyoming selling electricity to Los Angeles, California (U.S.A.), our results suggest that a generic CO2-BES design can increase the utilization of the HVDC transmission capacity, thereby increasing total revenue across combinations of electricity prices, wind conditions, and geothermal heat depletion. The CO2-BES facility could extract geothermal heat, dispatch geothermally generated electricity, and time-shift wind-generated electricity. With CO2-BES, total revenue always increases and the optimal HVDC transmission capacity increases in some combinations. To be profitable, the facility needs a modest $7.78/tCO2 to$10.20/tCO2, because its cost exceeds the increase in revenue. This last result highlights the need for further research to understand how to design a CO2-BES facility that is tailored to the geologic setting and its intended role in the energy system.
Recent advances in carbon capture storage and utilisation technologies: a review
Osman, A. , M. Hefny, M. Abdel Maksoud, A. Elgarahy, and D. Rooney, Environmental Chemistry Letters, 2020. [View Abstract]Human activities have led to a massive increase in CO2 emissions as a primary greenhouse gas that is contributing to climate change with >1°C global warming than that of the pre-industrial level. The three main technologies that are utilised in carbon capture; pre-combustion, post-combustion and oxy-fuel combustion, have been evaluated. We critically reviewed the advances in carbon capture, storage and utilisation in the recent literature. In this review, the affirmed carbon uptake technologies with techniques of carbon dioxide separation, as well as listing all the disadvantages and advantages of each technology, have been addressed. Monoethanolamine is the most common carbon sorbent; however, it requires high regeneration energy of 3.5 GJ per tonne of CO2, while recent advances in the sorbent technology showed novel solvent (Modulated Amine Blend) with lower regeneration energy of 2.17 GJ per tonne of CO2. Graphene type materials showed CO2 adsorption capacity of 0.07 mol/g, which is 10 times higher than that of specific types of activated carbon, zeolites and metal-organic frameworks. CO2 geosequestration provides an efficient and long-term strategy for storing the captured CO2 in geological formations with a global storage capacity factor at a Gt-scale within operational timescales. Regarding the utilisation route, currently, the gross global utilisation of CO2 is < 200 million tonnes/year, which is roughly negligible compared with the extent of global anthropogenic CO2 emissions (> 32,000 million tonnes/year). Herein, we reviewed different CO2 utilisation methods such as direct routes (i.e. beverage carbonation, food packaging and oil/gas recovery), material/chemical industries (i.e. acrylates, carbamates, carbonates, polyurethanes, polycarbonates, formaldehyde and urea) and fuels (i.e. biofuels, dimethyl ether, tertiary butyl methyl ether and methanol). Moreover, we investigated additional CO2 utilisation for base-load power generation, seasonal energy storage, and district cooling and/or cryogenic direct air CO2 capture using geothermal energy. Through bibliometric mapping, we identified the research gap in the literature within this field which requires future investigations, for instance, designing new and stable ionic liquids, pore size and selectivity of metal-organic frameworks and enhancing the adsorption capacity of novel solvents. Moreover, areas such as techno-economic evaluation of novel solvents, process design and dynamic simulation require further effort as well as research and development before pilot and commercial-scale trials.
Heat Depletion in Sedimentary Basins and its Effect on the Design and Electric Power Output of CO2 Plume Geothermal (CPG) Systems
Adams, B.M., D. Vogler, T.H. Kuehn, J.M. Bielicki, N. Garapati, and M.O. Saar, Renewable Energy, (in press). [View Abstract]CO2 Plume Geothermal (CPG) energy systems circulate geologically stored CO2 to extract geothermal heat from naturally permeable sedimentary basins. CPG systems can generate more electricity than brine systems in geologic reservoirs with moderate temperature and permeability. Here, we numerically simulate the temperature depletion of a sedimentary basin and find the corresponding CPG electricity generation variation over time. We find that for a given reservoir depth, temperature, thickness, permeability, and well configuration, an optimal well spacing provides the largest average electric generation over the reservoir lifetime. If wells are spaced closer than optimal, higher peak electricity is generated, but the reservoir heat depletes more quickly. If wells are spaced greater than optimal, reservoirs maintain heat longer but have higher resistance to flow and thus lower peak electricity is generated. Additionally, spacing the wells 10% greater than optimal affects electricity generation less than spacing wells 10% closer than optimal. Our simulations also show that for a 300 m thick reservoir, a 707 m well spacing provides consistent electricity over 50 years, whereas a 300 m well spacing yields large heat and electricity reductions over time. Finally, increasing injection or production well pipe diameters does not necessarily increase average electric generation.
Combining brine or CO2 geothermal preheating with low-temperature waste heat: A higher-efficiency hybrid geothermal power system
Garapati, N., B.M. Adams, M.R. Fleming, T.H. Kuehn, and M.O. Saar, Journal of CO2 Utilization, 42, 2020. [View Abstract]Hybrid geothermal power plants operate by using geothermal fluid to preheat the working fluid of a higher temperature power cycle for electricity generation. This has been shown to yield higher electricity generation than the combination of a stand-alone geothermal power plant and the higher-temperature power cycle. Here, we test both a direct CO2 hybrid geothermal system and an indirect brine hybrid geothermal system. The direct CO2 hybrid geothermal system is a CO2 Plume Geothermal (CPG) system, which uses CO2 as the subsurface working fluid, but with auxiliary heat addition to the geologically produced CO2 at the surface. The indirect brine geothermal system uses the hot geologically produced brine to preheat the secondary working fluid (CO2) within a secondary power cycle. We find that the direct CPG-hybrid system and the indirect brine-hybrid system both can generate 20 % more electric power than the summed power of individual geothermal and auxiliary systems in some cases. Each hybrid system has an optimum turbine inlet temperature which maximizes the electric power generated, and is typically between 100 ◦C and 200 ◦C in the systems examined. The optimum turbine inlet temperature tends to occur where the geothermal heat contribution is between 50 % and 70 % of the total heat addition to the hybrid system. Lastly, the CO2 direct system has lower wellhead temperatures than indirect brine and therefore can utilize lower temperature resources.
Permeability Impairment and Salt Precipitation Patterns during CO2 Injection into Single Natural Brine-filled Fractures
Lima, M., P. Schädle, C. Green, D. Vogler, M.O. Saar, and X.-Z. Kong, Water Resources Research, 56/8, pp. e2020WR027213, 2020. [View Abstract]Formation dry-out in fracture-dominated geological reservoirs may alter the fracture space, impair rock absolute permeability and cause a significant decrease in well injectivity. In this study, we numerically model the dry-out processes occurring during supercritical CO2 (scCO2) injection into single brine-filled fractures and evaluate the potential for salt precipitation under increasing effective normal stresses in the evaporative regime. We use an open-source, parallel finite-element framework to numerically model two-phase flow through 2-Dimensional fracture planes with aperture fields taken from naturally fractured granite cores at the Grimsel Test Site in Switzerland. Our results reveal a displacement front and a subsequent dry-out front in all simulated scenarios, where higher effective stresses caused more flow channeling, higher rates of water evaporation and larger volumes of salt precipitates. However, despite the larger salt volumes, the permeability impairment was lower at higher effective normal stresses. We conclude that the spatial distribution of the salt, precipitated in fractures with heterogeneous aperture fields, strongly affects the absolute permeability impairment caused by formation dry-out. The numerical simulations assist in understanding the behavior of the injectivity in fractures and fracture networks during subsurface applications that involve scCO2 injection into brine.
Identifying Geologic Characteristics and Operational Decisions to Meet Global Carbon Sequestration Goals
Middleton, R, J Ogland-Hand, B Chen, J Bielicki, K Ellet, D Harp, and R Kammer, Energy and Environmental Science, 2020.
Synchrotron-based pore-network modeling of two-phase flow in Nubian Sandstone and implications for capillary trapping of carbon dioxide
Hefny, M., C.-Z. Qin, M.O. Saar, and A. Ebigbo, International Journal of Greenhouse Gas Control, 103/1031642, 2020. [View Abstract]Depleted oil fields in the Gulf of Suez (Egypt) can serve as geothermal reservoirs for power production using a CO2-Plume Geothermal (CPG) system, while geologically sequestering CO2. This entails the injection of a substantial amount of CO2 into the highly permeable brine-saturated Nubian Sandstone. Numerical models of two-phase flow processes are indispensable for predicting the CO2-plume migration at a representative geological scale. Such models require reliable constitutive relationships, including relative permeability and capillary pressure curves. In this study, quasi-static pore-network modeling has been used to simulate the equilibrium positions of fluid-fluid interfaces, and thus determine the capillary pressure and relative permeability curves. Three-dimensional images with a voxel size of 0.65 μm3 of a Nubian Sandstone rock sample have been obtained using Synchrotron Radiation X-ray Tomographic Microscopy. From the images, topological properties of pores/throats were constructed. Using a pore-network model, we performed a sequential primary drainage–main imbibition cycle of quasi-static invasion in order to quantify (1) the CO2 and brine relative permeability curves, (2) the effect of initial wetting-phase saturation (i.e. the saturation at the point of reversal from drainage to imbibition) on the residual–trapping potential, and (3) study the relative permeability–saturation hysteresis. The results illustrate the sensitivity of the pore-scale fluid-displacement and trapping processes on some key parameters (i.e. advancing contact angle, pore-body-to-throat aspect ratio, and initial wetting-phase saturation) and improve our understanding of the potential magnitude of capillary trapping in Nubian Sandstone.
Strength and deformability of a low-porosity sandstone under true triaxial compression conditions
Zhang, S., S.-C. Wu, and G. Zhang, International Journal of Rock Mechanics and Mining Sciences, 127/104204, 2020.