Martin O. Saar


Last Name

Saar

First Name

Martin O.

ORCID

0000-0002-4869-6452

Organisational unit

09494 - Saar, Martin O. / Saar, Martin O.

Search Results

Publications 1 - 10 of 100
  • Shear induced flow path evolution in rough-wall fractures: A Particle Image Velocimetry examination
    Item type: Journal Article
    Naets, Isamu; Ahkami, Mehrdad; Huang, Po-Wei; et al. (2022)
    Journal of Hydrology
    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 tecques 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.
  • CCS coupled with CO2 plume geothermal operations: Enhancing CO2 sequestration and reducing risks
    Item type: Journal Article
    Hau, Kevin Peter; Brehme, Maren; Rangriz Shokri, Alireza; et al. (2025)
    Geothermics
    The transition to a low-carbon economy is essential for mitigating climate change, particularly in hard-to-abate sectors. Carbon Capture Utilisation and Storage (CCUS) is expected to play a pivotal role in this transition. This numerical study integrates CO₂ Plume Geothermal (CPG) systems with conventional CCS using field data from the Aquistore CCS project. By employing an integrated subsurface-surface modelling workflow, we simulate and compare two 30-year scenarios with nearly identical masses of sequestered CO₂: a) Business-as-usual CCS and b) coupled CPG-CCUS The results suggest that coupled CPG-CCUS operations provide a stable source of geothermal energy, which could potentially reduce or offset energy costs, such as those associated with the CO₂ capturing process. Additionally, coupling CPG with CCS enhances CO₂ sequestration efficiency by increasing CO₂ mass density in reservoir regions that become thermally depleted due to the sustained injection of CO₂ at temperatures lower than the native reservoir temperature. Although thermally depleted regions develop during both CCS and CPG-CCUS operations, they are significantly more pronounced during the latter due to the combined effect of both cold CO₂ injection and heat extraction. Moreover, CPGCCUS operations result in a more concentrated CO₂ plume around the wells. While the production well induces a pressure gradient, this gradient primarily directs fluid flow along the injection-to-production well axis, effectively focusing the CO₂ plume and limiting widespread lateral diffusion of the fluids (brine and CO₂) to the far-field reservoir. This localised CO₂ accumulation improves CO₂ plume control and reduces risks associated with uncontrolled CO₂ migration, thereby enhancing the predictability of CO₂ accumulation. This synergistic combination of CCS and CPG operations offers a pathway for the energy transition, enhancing both the CCS technology and the geothermal resource potential, while improving CO₂ sequestration safety.
  • GeoProp: A thermophysical property modelling framework for single and two-phase geothermal geofluids
    Item type: Journal Article
    Merbecks, Tristan Leonard; Moreira Mulin Leal, Allan; Bombarda, Paola; et al. (2025)
    Geothermics
    The techno-economic evaluation of geothermal resources requires knowledge of the geofluid's thermophysical properties. While the properties of pure water and some specific brines have been studied extensively, no universally applicable model currently exists. This can result in a considerable degree of uncertainty as to how different geothermal resources will perform in practice. Geofluid modelling has historically been focused on two research fields: 1) partitioning the geofluid into separate phases, and 2) the estimation of the phases’ thermophysical properties. Models for the two fields have commonly been developed separately. Recognising their potential synergy, we introduce GeoProp, a novel geofluid modelling framework, which addresses this application gap by coupling existing state-of-the-art fluid partitioning simulators, such as Reaktoro, with high-accuracy thermophysical fluid property computation engines, like CoolProp and ThermoFun. GeoProp has been validated against field experimental data as well as existing models for some incompressible binary fluids. We corroborate GeoProp's efficacy at modelling the thermophysical properties of geothermal geofluids via a case study on the heat content of different geofluids. Our results highlight the importance of accurately characterising the thermophysical properties of geofluids in order to quantify the resource potential and optimise the design of geothermal power plants.
  • Swiss Potential for Geothermal Energy and CO2 Storage
    Item type: Report
    Driesner, Thomas; Gischig, Valentin; Hertrich, Marian; et al. (2021)
  • Multi-disciplinary characterizations of the Bedretto Lab – a unique underground geoscience research facility
    Item type: Working Paper
    Ma, Xiaodong; Hertrich, Marian; Amann, Florian; et al. (2021)
    Solid Earth Discussions
    The increased interest in subsurface development (e.g., unconventional hydrocarbon, deep geothermal, waste disposal) and the associated (triggered or induced) seismicity calls for a better understanding of the hydro-seismo-mechanical coupling in fractured rock masses. Being able to bridge the knowledge gap between laboratory and reservoir scales, controllable meso-scale in situ experiments are deemed indispensable. In an effort to access and instrument rock masses of hectometer size, the Bedretto Underground Laboratory for Geosciences and Geoenergies (‘Bedretto Lab’) was established in 2018 in the existing Bedretto Tunnel (Ticino, Switzerland), with an average overburden of 1000 m. In this paper, we introduce the Bedretto Lab, its general setting and current status. Combined geological, geomechanical and geophysical methods were employed in a hectometer-scale rock mass explored by several boreholes to characterize the in situ conditions and internal structures of the rock volume. The rock volume features three distinct units, with the middle fault zone sandwiched by two relatively intact units. The middle fault zone unit appears to be a representative feature of the site, as similar structures repeat every several hundreds of meters along the tunnel. The lithological variations across the characterization boreholes manifest the complexity and heterogeneity of the rock volume, and are accompanied by compartmentalized hydrostructures and significant stress rotations. With this complexity, the characterized rock volume is considered characteristic of the heterogeneity that is typically encountered in subsurface exploration and development. The Bedretto Lab can adequately serve as a test-bed that allows for in-depth study of the hydro-seismo-mechanical response of fractured crystalline rock masses.
  • CO2-Plume Geothermal: Enabling CCS
    Item type: Other Conference Item
    de Reus, Jasper; Onishi, Tsubasa; Küçük, Serhat; et al. (2024)
  • What can pore-scale optical measurements do?
    Item type: Other Conference Item
    Kong, Xiang-Zhao; Naets, Isamu; Ahkami, Mehrdad; et al. (2022)
    Abstract Volume 20th Swiss Geoscience Meeting
  • CO₂-Plume Geothermal (CPG) after enhanced oil recovery (EOR)
    Item type: Journal Article
    Kucuk , Serhat; Farajzadeh , Rouhollah; Brehme , Maren; et al. (2026)
    Geoenergy Science and Engineering
    The global energy transition requires novel carbon utilization methods to enable integrated and optimized low-carbon energy production. Coupling CO₂-based geothermal energy extraction with CO₂-enhanced oil recovery (EOR) represents a promising yet largely unexplored approach for improving resource efficiency and carbon sequestration. This study investigates the integration of CO₂-Plume Geothermal (CPG) energy production with CO₂-EOR in mature oil reservoirs using numerical simulations of conceptual heterogeneous reservoir models. The interplay between EOR and CPG performance in terms of energy production and CO₂ storage is evaluated and compared to understand the geotechnical implications of this integration. The analysis highlights that initiating CPG operations after EOR significantly benefits from the established CO₂ plume, facilitating immediate and efficient geothermal energy extraction. Results show that integrating CPG with EOR increases total energy recovery by 20%–50% relative to the energy produced by EOR alone, yielding CPG thermal power outputs ranging from 13 to 23 MWₜₕ/km². Continued CO₂ injection during CPG operations further increases total CO₂ storage by 80%–280%, driven primarily by improved volumetric sweep of previously unswept reservoir volumes and enhanced CO₂ density resulting from reservoir cooling. While reservoir heterogeneity strongly influences oil recovery during EOR, its effect on CPG thermal output is less pronounced, since native reservoir fluids (oil and brine) have already been largely displaced during the EOR stage, and the CO₂ plume gradually stabilizes over time. These findings demonstrate the viability and advantages of integrated CO₂-EOR and CPG systems, offering insights into novel methods essential for sustainable subsurface resource management and climate-change mitigation.
  • Numerical Modeling to Study the Impact of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling (PPGD)
    Item type: Other Conference Item
    Ezzat, Mohamed; Vogler, Daniel; Adams, Benjamin; et al. (2021)
    Reducing the cost of drilling is crucial to economically extract deep geothermal energy as drilling costs can reach up to 70% of the total investment budget (Tester et al. 2006). Unfortunately, traditional mechanical rotary drilling is often far too expensive to enable economical geothermal energy extraction from many deep geologic settings due to the amount of energy rotary drilling requires and due to its significant drill bit wear, causing long, unproductive tripping times to exchange worn drill heads (Schiegg et al. 2015). To reduce deep geothermal drilling costs, novel drilling technologies are required, such as Plasma Pulse Geo Drilling (PPGD) as well as thermal spallation, laser, and microwave drilling, to name a few (Woskov et al. 2014; Buckstegge et al. 2016; Vogler et al. 2020; Walsh et al. 2020). PPGD is a so-called contact-less drilling technology that uses high-voltage electricity pulses >200 kV that last for ∼2 microseconds to fracture the rock, thereby drilling without mechanical abrasion, reducing/eliminating costly, unproductive tripping times and requiring less energy to break the rock than rotary drilling. Experimentally, Anders et al. 2017 found that PPGD is ∼17% cheaper than mechanical rotary drilling. Analytical studies by Rodland 2012 and Schiegg et al. 2015 suggested that further research could possibly reduce PPGD drilling costs by as much as ∼90% of current mechanical rotary drilling costs. Nonetheless, the fundamental physics that underlies the PPGD process is still poorly understood, and the feasibility of PPGD under deep wellbore conditions requires further investigations. (Zhu et al. 2021) investigated numerically how the local electric breakdown in pores can lead to electric breakdown occurrence across the entire rock sample. Numerically, Ezzat et al. 2021 found that the plasma pressure generated due to the localized electric breakdown in rock pores is high enough to induce rock fracturing for specific conditions, resulting in drilling success. Here, we present our preliminary numerical modeling results concerning the influence of rock pore characteristics, such as pore fluid, shape, and size on the localized electric breakdown of rock. Our goal is to eventually use these results to further increase the efficiency, and thus, further reduce the costs, of PPGD. Our results show that PPGD is facilitated if the rock pores are filled with a gas and not with water, which is consistent with the experimental findings of Lisitsyn et al. 1998 and Inoue et al. 1999. Also, our results suggest that larger pore sizes and smaller pore pressures are more favorable for PPGD. These findings are valid until ∼1 MPa pore pressure. To extend our model to cover higher pressure ranges, further physical lab experiments are required that investigate the electric breakdown of air at high gas pressures >1 MPa.
  • Validating the Nernst-Planck transport model under reaction-driven flow conditions using RetroPy v1.0
    Item type: Journal Article
    Huang, Po-Wei; Flemisch, Bernd; Qin, Chao-Zhong; et al. (2023)
    Geoscientific Model Development
    Reactive transport processes in natural environments often involve many ionic species. The diffusivities of ionic species vary. Since assigning different diffusivities in the advection-diffusion equation leads to charge imbalance, a single diffusivity is usually used for all species. In this work, we apply the Nernst-Planck equation, which resolves unequal diffusivities of the species in an electroneutral manner, to model reactive transport. To demonstrate the advantages of the Nernst-Planck model, we compare the simulation results of transport under reaction-driven flow conditions using the Nernst-Planck model with those of the commonly used single-diffusivity model. All simulations are also compared to well-defined experiments on the scale of centimeters. Our results show that the Nernst-Planck model is valid and particularly relevant for modeling reactive transport processes with an intricate interplay among diffusion, reaction, electromigration, and density-driven convection.
Publications 1 - 10 of 100