# 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

28.06.2022

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16.06.2022

#### First Prize Geoverbund ABC/J Young Academics Award 2022 – Dr. Paromita Deb

Paromita Deb has been awarded 1st prize by the Geoverbund ABC/J Young Academics Award 2022 for her doctoral dissertation.

31.05.2022

#### Research program of Dr. Maren Brehme supported by Energi Simulation organization

We are pleased to announce the formation of a new group, to conduct research into the safe, effective and efficient exploration and operation of geothermal energy systems.

02.05.2022

#### Doctoral Examination Hoda Javanmard

On Friday, April 29th, Hoda Javanmard has successfully defended her PhD thesis, titled: “Hydromechanical processes in natural and 3D printed fractures”

11.04.2022

#### SASEG Student Grant

Dario Schwendener
For his ongoing Master Thesis Project, “Velocity Quantification of Two Phase Drainage and Imbibition Processes in Rough Wall Fractures”, Dario Schwendener was awarded with the SASEG student grant of 1’000 CHF provided by the Swiss Association of Energy Geoscientists.

Within a 3D-printed, transparent fracture model, phase velocities are directly determined using the optical approach of particle image velocimetry (PIV).
The thesis is currently in the experimental stage and supervised by Dr. Xiang-Zhao Kong, PhD student Isamu Naets and Dr. Jérõme André Roland Noir.

31.01.2022

#### 2nd place in SPE GeoHackathon 2021

3 GEG PhD students together with PhD students from RWTH Aachen achieved 2nd Place in the 2021 SPE GeoHackathon. As part of the Hackathon, they were tasked with creating a field development plan for a site in the Netherlands to provide heat to local demand points at a minimum levelised cost of heat over a 20 year period.
Experience of PhD students – hover over arrow

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.

# 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

16.08.2022    14:15-15:15
EOR: experiences deploying subsurface technology from the lab to the field

Jasper de Reus (GEG group presentation)
GEG Meetings, ETH Zurich

NEXT EVENT
23.08.2022    14:15-15:15
Doctoral defense practice talk

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

30.08.2022    14:15-15:15
Update progress / Practice research plan defence

Anna Kottsova (GEG group presentation)
GEG Meetings, ETH Zurich

06.09.2022    15:30-16:30
Overview AEGIS-CH Innosuisse Flagship Project
Speakers: Martin Saar, Andreas Reinicke, Jasper de Reus

Martin Saar (GEG group presentation)
GEG Meetings, ETH Zurich

12.09.2022
Sensitivity of phase tensors to absolute resistivities in a 3-D world

Luise Dambly (poster presentation)
EM induction workshop, Cesme, Turkey

13.09.2022    14:15-15:15
GEG 2022/2023 academic year kickoff meeting + Apero afterwards

Martin Saar (GEG group presentation)
GEG Meetings, ETH Zurich

20.09.2022    14:15-15:15
Verification of numerical tools for EGS design using benchmark laboratory-scale experiments

Paromita Deb (GEG group presentation)
GEG Meetings, ETH Zurich

21.09.2022    10:05-11:10 (local time)
How CO2-based geothermal energy extraction and utilization can accelerate storage of the entire CO2 - true CCUS

Martin Saar (invited talk)
CO2GeoNet Open Forum, San Servolo Island – Venice – Italy

04.10.2022    14:15-15:15
Secondment Summary

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

11.10.2022    14:15-15:15
Practice: Ph.D defense

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

17.10.2022
Updated Conceptual Models of the Lahendong High-Enthalpy Geothermal Field

Lily Suherlina (contributed talk)
EGC2022, Berlin

01.11.2022    14:15-15:15
Using magnetotellurics for capturing geological controls on the formation of intermediate-temperature geothermal resources

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

15.11.2022    14:15-15:15
Update progress : history production matching model

Lily Suherlina (GEG group presentation)
GEG Meetings, ETH Zurich

06.12.2022    14:15-15:15
MT studies in Ethiopia

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

13.12.2022    14:15-15:15
A new chemical kinetics algorithm in Reaktoro v2

Allan Leal (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

The role of high-permeability inclusion on solute transport in a 3D-printed fractured porous medium: An LIF-PIV integrated study
Kong, X.-Z., M. Ahkami, I. Naets, and M.O. Saar, Transport in Porous Media, (in press). [View Abstract]It is well-known that the presence of geometry heterogeneity in porous media enhances solute mass mixing due to fluid velocity heterogeneity. However, laboratory measurements are still sparse on characterization of the role of high-permeability inclusions on solute transport, in particularly concerning fractured porous media. In this study, the transport of solutes is quantified after a pulse-like injection of soluble fluorescent dye into a 3D-printed fractured porous medium with distinct high-permeability (H-k) inclusions. The solute concentration and the pore-scale fluid velocity are determined using laser-induced fluorescence and particle image velocimetry techniques. The migration of solute is delineated with its breakthrough curve (BC), temporal and spatial moments, and mixing metrics (including the scalar dissipation rate, the volumetric dilution index, and the flux-related dilution index) in different regions of the medium. With the same H-k inclusions, compared to a H-k matrix, the low-permeability (L-k) matrix displays a higher peak in its BC, less solute mass retention, a higher peak solute velocity, a smaller peak dispersion coefficient, a lower mixing rate, and a smaller pore volume being occupied by the solute. The flux-related dilution index clearly captures the striated solute plume tails following the streamlines along dead-end fractures and along the interface between the H-k and L-k matrices. We propose a normalization of the scalar dissipation rate and the volumetric dilution index with respect to the maximum regional total solute mass, which offers a generalized examination of solute mixing for an open region with a varying total solute mass. Our study presents insights into the interplay between the geometric features of the fractured porous medium and the solute transport behaviors at the pore scale. (Paper accepted 2022-07-07)
The Dynamic Evolution of the Lahendong Geothermal System in North-Sulawesi, Indonesia.
Suherlina, L, J Newson, Y Kamah, and M Brehme, Geothermics , 105, pp. 1-19, 2022. [View Abstract]This study uses an integrated approach to characterize the dynamic evolution of the power- producing high-enthalpy geothermal system of Lahendong, North-Sulawesi, Indonesia. Lahendong has two primary reservoirs, the southern and the northern, which have been utilised for electricity production for more than twenty years. The main focus of this study is the characterisation of heat and mass flows in the system with respect to geological structures and permeability distribution. Also, it delineates how the geothermal system has evolved and the spatial variation of the response resulting from prolonged utilization of the reservoirs. This research implemented geological structure analysis on recent surface fault mapping and pre-existing fault studies from literature. Further, the study analysed well data comprising well pressure, enthalpy, drilling program reviews and tracer tests. Hydrochemical investigation compiled new and old surface and subsurface hydrochemical evolution in both the temporal and spatial domain. The results confirm several trends of faults in the study area: NE-SW and NW-SE are the major striking directions, while E-W and N-S are less dominant. The most apparent trends are NE- SW striking strike-slip faults, perpendicular NW-SE thrust faults and N-S and E-W striking normal faults. The faults compartmentalize the reservoir. A comparison of the southern and the northern reservoir shows that the south is more structurally controlled by faults; both reservoirs rely on fractures as permeability provider and are controlled by shallow hydrogeology, derived from the integrated analysis of transient well data. Geochemical analysis shows that the reservoir fluids have generally higher Electrical Conductivity and closer to fluid-rock equilibrium, probably due to boiling. Spring waters have generally become more acidic, which is an expected result of reservoir boiling and increased steam input to near-surface waters. The spatial distribution of changes shows permeability evolution over time and also the role of structural permeability in response to changing reservoir conditions. Observing and recording reservoir data is highly important to understand the reservoir response to production and ensure the long-term sustainability of the system. Additionally, the data is critical for making a major difference in the reservoir management strategy. (Paper accepted 2022-06-25)
Using CO2-Plume Geothermal (CPG) Energy Technologies to Support Wind and Solar Power in Renewable-Heavy Electricity Systems
van Brummen, A.C., B.M. Adams, R. Wu, J.D. Ogland-Hand, and M.O. Saar, Renewable and Sustainable Energy Transition, (in press). [View Abstract]CO2-Plume Geothermal (CPG) technologies are geothermal power systems that use geologically stored CO2 as the subsurface heat extraction fluid to generate renewable energy. CPG technologies can support variable wind and solar energy technologies by providing dispatchable power, while Flexible CPG (CPG- F) facilities can provide dispatchable power, energy storage, or both simultaneously. We present the first study investigating how CPG power plants and CPG-F facilities may operate as part of a renewable- heavy electricity system by integrating plant-level power plant models with systems-level optimization models. We use North Dakota, USA as a case study to demonstrate the potential of CPG to expand the geothermal resource base to locations not typically considered for geothermal power. We find that optimal system capacity for a solar-wind-CPG model can be up to 20 times greater than peak- demand. CPG-F facilities can reduce this modeled system capacity to just over 2 times peak demand by providing energy storage over both seasonal and short-term timescales. The operational flexibility of CPG-F facilities is further leveraged to bypass the ambient air temperature constraint of CPG power plants by storing energy at critical temperatures. Across all scenarios, a tax on CO2 emissions, on the order of hundreds of dollars per tonne, is required to financially justify using renewable energy over natural-gas power plants. Our findings suggest that CPG and CPG-F technologies may play a valuable role in future renewable-heavy electricity systems, and we propose a few recommendations to further study its integration potential. (Paper accepted 2022-06-16)
Relating Darcy-scale chemical reaction order to pore-scale spatial heterogeneity
Huang, P.-W., B. Flemisch, C.-Z. Qin, M.O. Saar, and A. Ebigbo, Transport in Porous Media, 2022. [View Abstract]Due to spatial scaling effects, there is a discrepancy in mineral dissolution rates measured at different spatial scales. Many reasons for this spatial scaling effect can be given. We investigate one such reason, i.e., how pore-scale spatial heterogeneity in porous media affects overall mineral dissolution rates. Using the bundle-of-tubes model as an analogy for porous media, we show that the Darcy-scale reaction order increases as the statistical similarity between the pore sizes and the effective-surface-area ratio of the porous sample decreases. The analytical results quantify mineral spatial heterogeneity using the Darcy-scale reaction order and give a mechanistic explanation to the usage of reaction order in Darcy-scale modeling. The relation is used as a constitutive relation of reactive transport at the Darcy scale. We test the constitutive relation by simulating flow-through experiments. The proposed constitutive relation is able to model the solute breakthrough curve of the simulations. Our results imply that we can infer mineral spatial heterogeneity of a porous media using measured solute concentration over time in a flow-through dissolution experiment. (Paper accepted 2022-06-08)
Inverse chemical equilibrium problems: General formulation and algorithm
Leal, A.M.M., and W. R. Smith, Chemical Engineering Science, 252/28, pp. 1-20, 2022. [View Abstract]In a forward chemical equilibrium problem (FCEP), the state of minimum Gibbs energy for a chemical system is sought, in which temperature, pressure, elemental amounts, and thermodynamic model parameters are prescribed. We herein present a mathematical framework for characterizing and solving inverse chemical equilibrium problems (ICEP), a class of problems for which one or more of those prescribed conditions in a FCEP are unknown in advance. In an ICEP, complementary conditions must be imposed, which are referred to here as equilibrium constraints. Examples of ICEPs include those in which a certain property is known at equilibrium (e.g., volume is specified instead of pressure; enthalpy is specified instead of temperature; pH is specified instead of the amount of element H). The equilibrium constraints may also be specified by equations that govern the relationship between several equilibrium properties (e.g., the equations relating temperature, pressure, density, energy, and velocity of the gases produced during the detonation of an explosive). (Paper accepted 2022-04-28)
Implementing an Equation of State without Derivatives: teqp
H. Bell, I., U. K. Deiters, and A.M.M. Leal, Industrial & Engineering Chemistry Research, 61/17, pp. 6010-6027, 2022. [View Abstract]This work uses advanced numerical techniques (complex differentiation and automatic differentiation) to efficiently and accurately compute all the required thermodynamic properties of an equation of state without any analytical derivatives─particularly without any handwritten derivatives. It avoids the tedious and error-prone process of symbolic differentiation, thus allowing for more rapid development of new thermodynamic models. The technique presented here was tested with several equations of state (van der Waals, Peng–Robinson, Soave–Redlich–Kwong, PC-SAFT, and cubic-plus-association) and high-accuracy multifluid models. A minimal set of algorithms (critical locus tracing and vapor–liquid equilibrium tracing) were implemented in an extensible and concise open-source C++ library: teqp (for Templated EQuation of state Package). This work demonstrates that highly complicated equations of state can be implemented faster yet with minimal computational overhead and negligible loss in numerical precision compared with the traditional approach that relies on analytical derivatives. We believe that the approach outlined in this work has the potential to establish a new computational standard when implementing computer codes for thermodynamic models. (Paper accepted 2022-04-26)
Shear induced fluid flow path evolution in rough-wall fractures: A particle image velocimetry examination
Naets, I., M. Ahkami, P.-W. Huang, M. O. Saar, and X.-Z. Kong, Journal of Hydrology, 610/127793, 2022. [View Abstract]Rough-walled fractures in rock masses, as preferential pathways, largely influence fluid flow, solute and energy transport. Previous studies indicate that fracture aperture fields could be significantly modified due to shear displacement along fractures. We report experimental observations and quantitative analyses of flow path evolution within a single fracture, induced by shear displacement. Particle image velocimetry and refractive index matching techniques were utilized to determine fluid velocity fields inside a transparent 3D-printed shear-able rough fracture. Our analysis indicate that aperture variability and correlation length increase with the increasing shear displacement, and they are the two key parameters, which govern the increases in velocity variability, velocity longitudinal correlation length, streamline tortuosity, and variability of streamline spacing. The increase in aperture heterogeneity significantly impacts fluid flow behaviors, whilst changes in aperture correlation length further refine these impacts. To our best knowledge, our study is the first direct measurements of fluid velocity fields and provides insights into the impact of fracture shear on flow behavior. (Paper accepted 2022-04-03)
The Importance of Modeling Carbon Dioxide Transportation and Geologic Storage in Energy System Planning Tools
Ogland-Hand, J.D., S.M. Cohen, R.M. Kammer, K.M. Ellett, M.O. Saar, and J.A. Bennett, Frontiers, 10/855105, 2022. [View Abstract]Energy system planning tools suggest that the cost and feasibility of climate-stabilizing energy transitions are sensitive to the cost of CO2 capture and storage processes (CCS), but the representation of CO2 transportation and geologic storage in these tools is often simple or non-existent. We develop the capability of producing dynamic-reservoir-simulation-based geologic CO2 storage supply curves with the Sequestration of CO2 Tool (SCO2T) and use it with the ReEDS electric sector planning model to investigate the effects of CO2 transportation and geologic storage representation on energy system planning tool results. We use a locational case study of the Electric Reliability Council of Texas (ERCOT) region. Our results suggest that the cost of geologic CO2 storage may be as low as $3/tCO2 and that site-level assumptions may affect this cost by several dollars per tonne. At the grid level, the cost of geologic CO2 storage has generally smaller effects compared to other assumptions (e.g., natural gas price), but small variations in this cost can change results (e.g., capacity deployment decisions) when policy renders CCS marginally competitive. The cost of CO2 transportation generally affects the location of geologic CO2 storage investment more than the quantity of CO2 captured or the location of electricity generation investment. We conclude with a few recommendations for future energy system researchers when modeling CCS. For example, assuming a cost for geologic CO2 storage (e.g.,$5/tCO2) may be less consequential compared to assuming free storage by excluding it from the model. (Paper accepted 2022-02-25)
Review: Induced Seismicity during Geoenergy Development - a Hydromechanical Perspective
Ge, S., and M.O. Saar, Journal of Geophysical Research: Solid Earth, 127/e2021JB02314, 2022. [View Abstract]The basic triggering mechanism underlying induced seismicity traces back to the mid-1960s that relied on the process of pore-fluid pressure diffusion. The last decade has experienced a renaissance of induced seismicity research and data proliferation. An unprecedent opportunity is presented to us to synthesize the robust growth in knowledge. The objective of this paper is to provide a concise review of the triggering mechanisms of induced earthquakes with a focus on hydro-mechanical processes. Four mechanisms are reviewed: pore-fluid pressure diffusion, poroelastic stress, Coulomb static stress transfer, and aseismic slip. For each, an introduction of the concept is presented, followed by case studies. Diving into these mechanisms sheds light on several outstanding questions. For example, why did some earthquakes occur far from fluid injection or after injection stopped? Our review converges on the following conclusions: (1) Pore-fluid pressure diffusion remains a basic mechanism for initiating inducing seismicity in the near-field. (2) Poroelastic stresses and aseismic slip play an important role in inducing seismicity in regions beyond the influence of pore-fluid pressure diffusion. (3) Coulomb static stress transfer from earlier seismicity is shown to be a viable mechanism for increasing stresses on mainshock faults. (4) Multiple mechanisms have operated concurrently or consecutively at most induced seismicity sites. (5) Carbon dioxide injection is succeeding without inducing earthquakes and much can be learned from its success. Future research opportunities exist in deepening the understanding of physical and chemical processes in the nexus of geoenergy development and fluid motion in the Earth’s crust. (Paper accepted 2022-02-21)