159 results on '"Martin O. Saar"'
Search Results
2. Using CO2-Plume geothermal (CPG) energy technologies to support wind and solar power in renewable-heavy electricity systems
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Anna C. Van Brummen, Benjamin M. Adams, Raphael Wu, Jonathan D. Ogland-Hand, and Martin O. Saar
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Renewable energy integration ,CO2 Plume geothermal ,Seasonal energy storage ,Long duration energy storage ,Sedimentary basin geothermal resources ,Renewable energy sources ,TJ807-830 - 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.
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- 2022
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3. The Importance of Modeling Carbon Dioxide Transportation and Geologic Storage in Energy System Planning Tools
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Jonathan D. Ogland-Hand, Stuart M. Cohen, Ryan M. Kammer, Kevin M. Ellett, Martin O. Saar, Jeffrey A. Bennett, and Richard S. Middleton
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energy system planning ,ReEDS ,SCO2T ,CCS ,supply curve ,geologic CO2 storage ,General Works - 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.
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- 2022
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4. A numerical investigation into key factors controlling hard rock excavation via electropulse stimulation
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Daniel Vogler, Stuart D.C. Walsh, and Martin O. Saar
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Electropulse stimulation ,High voltage breakdown ,Numerical modeling ,Drilling ,Thermo-mechanics ,Engineering geology. Rock mechanics. Soil mechanics. Underground construction ,TA703-712 - Abstract
Electropulse stimulation provides an energy-efficient means of excavating hard rocks through repeated application of high voltage pulses to the rock surface. As such, it has the potential to confer significant advantages to mining and drilling operations for mineral and energy resources. Nevertheless, before these benefits can be realized, a better understanding of these processes is required to improve their deployment in the field. In this paper, we employ a recently developed model of the grain-scale processes involved in electropulse stimulation to examine excavation of hard rock under realistic operating conditions. To that end, we investigate the maximum applied voltage within ranges of 120–600 kV, to observe the onset of rock fragmentation. We further study the effect of grain size on rock breakage, by comparing fine (granodiorite) and coarse grained (granite) rocks. Lastly, the pore fluid salinity is investigated, since the electric conductivity of the pore fluid is shown to be a governing factor for the electrical conductivity of the modeled system. This study demonstrates that all investigated factors are crucial to the efficiency of rock fragmentation by electropulsing.
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- 2020
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5. Solute tracer test quantification of the effects of hot water injection into hydraulically stimulated crystalline rock
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Anniina Kittilä, Mohammadreza Jalali, Martin O. Saar, and Xiang-Zhao Kong
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Geothermal energy ,Tracer test ,Moment analysis ,Hot water injection ,Hydraulic stimulation ,Crystalline rock ,Renewable energy sources ,TJ807-830 ,Geology ,QE1-996.5 - Abstract
Abstract When water is injected into a fracture-dominated reservoir that is cooler or hotter than the injected water, the reservoir permeability is expected to be altered by the injection-induced thermo-mechanical effects, resulting in the redistribution of fluid flow in the reservoir. These effects are important to be taken into account when evaluating the performance and lifetime particularly of Enhanced Geothermal Systems (EGS). In this paper, we compare the results from two dye tracer tests, conducted before (at ambient temperature of $$13\,^{\circ } \text {C}$$ 13 ∘ C ) and during the injection of $$45\,^{\circ } \text {C}$$ 45 ∘ C hot water into a fractured crystalline rock at the Grimsel Test Site in Switzerland. Conducting a moment analysis on the recovered tracer residence time distribution (RTD) curves, we observe, after hot water injection, a significant decrease in the total tracer recovery. This recovery decrease strongly suggests that fluid flow was redistributed in the studied rock volume and that the majority of the injected water was lost to the far-field. Furthermore, using temperature measurements, obtained from the same locations as the tracer RTD curves, we conceptualize an approach to estimate the fracture surface area contributing to the heat exchange between the host rock and the circulating fluid. Our moment analysis and simplified estimation of fracture surface area provide insights into the hydraulic properties of the hydraulically active fracture system and the changes in fluid flow. Such insights are important to assess the heat exchange performance of a geothermal formation during fluid circulation and to estimate the lifetime of the geothermal formation, particularly in EGS.
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- 2020
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6. The influence of thermal treatment on rock–bit interaction: a study of a combined thermo–mechanical drilling (CTMD) concept
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Edoardo Rossi, Martin O. Saar, and Philipp Rudolf von Rohr
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Thermal treatment ,Granite ,Deep geothermal ,Rock–bit ,Drilling performance ,Rock removal ,Renewable energy sources ,TJ807-830 ,Geology ,QE1-996.5 - Abstract
Abstract To improve the economics and viability of accessing deep georesources, we propose a combined thermo–mechanical drilling (CTMD) method, employing a heat source to facilitate the mechanical removal of rock, with the aim of increasing drilling performance and thereby reducing the overall costs, especially for deep wells in hard rocks. In this work, we employ a novel experiment setup to investigate the main parameters of interest during the interaction of a cutter with the rock material, and we test untreated and thermally treated sandstone and granite, to understand the underlying rock removal mechanism and the resulting drilling performance improvements achievable with the new approach. We find that the rock removal process can be divided into three main regimes: first, a wear-dominated regime, followed by a compression-based progression of the tool at large penetrations, and a final tool fall-back regime for increasing scratch distances. We calculate the compressive rock strengths from our tests to validate the above regime hypothesis, and they are in good agreement with literature data, explaining the strength reduction after treatment of the material by extensive induced thermal cracking of the rock. We evaluate the new method’s drilling performance and confirm that thermal cracks in the rock can considerably enhance subsequent mechanical rock removal rates and related drilling performance by one order of magnitude in granite, while mainly reducing the wear rates of the cutting tools in sandstone.
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- 2020
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7. A methodology to determine the elastic properties of anisotropic rocks from a single uniaxial compression test
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Morteza Nejati, Marie Luise Texas Dambly, and Martin O. Saar
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Engineering geology. Rock mechanics. Soil mechanics. Underground construction ,TA703-712 - Abstract
This paper introduces a new methodology to measure the elastic constants of transversely isotropic rocks from a single uniaxial compression test. We first give the mathematical proof that a uniaxial compression test provides only four independent strain equations. As a result, the exact determination of all five independent elastic constants from only one test is not possible. An approximate determination of the Young's moduli and the Poisson's ratios is however practical and efficient when adding the Saint–Venant relation as the fifth equation. Explicit formulae are then developed to calculate both secant and tangent definitions of the five elastic constants from a minimum of four strain measurements. The results of this new methodology applied on three granitic samples demonstrate a significant stress-induced nonlinear behavior, where the tangent moduli increase by a factor of three to four when the rock is loaded up to 20 MPa. The static elastic constants obtained from the uniaxial compression test are also found to be significantly smaller than the dynamic ones obtained from the ultrasonic measurements. Keywords: Transversely isotropic rock, Elastic constants, Young's modulus, Poisson's ratio, Seismic anisotropy, Uniaxial compression, Granite
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- 2019
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8. Thermally driven fracture aperture variation in naturally fractured granites
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Marina Grimm Lima, Daniel Vogler, Lorenzo Querci, Claudio Madonna, Bodo Hattendorf, Martin O. Saar, and Xiang-Zhao Kong
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Geothermal energy ,Rough fracture ,Fracture aperture evolution ,Thermo-hydro-mechanical-chemical (THMC) effects ,Pressure dissolution ,Fracture flow ,Renewable energy sources ,TJ807-830 ,Geology ,QE1-996.5 - Abstract
Abstract Temperature variations often trigger coupled thermal, hydrological, mechanical, and chemical (THMC) processes that can significantly alter the permeability/impedance of fracture-dominated deep geological reservoirs. It is thus necessary to quantitatively explore the associated phenomena during fracture opening and closure as a result of temperature change. In this work, we report near-field experimental results of the effect of temperature on the hydraulic properties of natural fractures under stressed conditions (effective normal stresses of 5–25 MPa). Two specimens of naturally fractured granodiorite cores from the Grimsel Test Site in Switzerland were subjected to flow-through experiments with a temperature variation of 25–140 °C to characterize the evolution of fracture aperture/permeability. The fracture surfaces of the studied specimens were morphologically characterized using photogrammetry scanning. Periodic measurements of the efflux of dissolved minerals yield the net removal mass, which is correlated to the inferred rates of fracture closure. Changes measured in hydraulic aperture are significant, exhibiting reductions of 20–75% over the heating/cooling cycles. Under higher confining stresses, the effects in fracture permeability are irreversible and notably time-dependent. Thermally driven fracture aperture variation was more pronounced in the specimen with the largest mean aperture width and spatial correlation length. Gradual fracture compaction is likely controlled by thermal dilation, mechanical grinding, and pressure dissolution due to increased thermal stresses exerted over the contacting asperities, as confirmed by the analyses of hydraulic properties and efflux mass.
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- 2019
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9. Using TNT-NN to unlock the fast full spatial inversion of large magnetic microscopy data sets
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Joseph M. Myre, Ioan Lascu, Eduardo A. Lima, Joshua M. Feinberg, Martin O. Saar, and Benjamin P. Weiss
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Magnetic microscopy ,Rock magnetism ,Non-negative least-squares ,Geography. Anthropology. Recreation ,Geodesy ,QB275-343 ,Geology ,QE1-996.5 - Abstract
Abstract Modern magnetic microscopy (MM) provides high-resolution, ultra-high-sensitivity moment magnetometry, with the ability to measure at spatial resolutions better than $$10^{-4}$$ 10-4 m and to detect magnetic moments weaker than $$10^{-15}$$ 10-15 Am$$^2$$ 2 . These characteristics make modern MM devices capable of particularly high-resolution analysis of the magnetic properties of materials, but generate extremely large data sets. Many studies utilizing MM attempt to solve an inverse problem to determine the magnitude of the magnetic moments that produce the measured component of the magnetic field. Fast Fourier techniques in the frequency domain and non-negative least-squares (NNLS) methods in the spatial domain are the two most frequently used methods to solve this inverse problem. Although extremely fast, Fourier techniques can produce solutions that violate the non-negativity of moments constraint. Inversions in the spatial domain do not violate non-negativity constraints, but the execution times of standard NNLS solvers (the Lawson and Hanson method and Matlab’s lsqlin) prohibit spatial domain inversions from operating at the full spatial resolution of an MM. In this paper, we present the applicability of the TNT-NN algorithm, a newly developed NNLS active set method, as a means to directly address the NNLS routine hindering existing spatial domain inversion methods. The TNT-NN algorithm enhances the performance of spatial domain inversions by accelerating the core NNLS routine. Using a conventional computing system, we show that the TNT-NN algorithm produces solutions with residuals comparable to conventional methods while reducing execution time of spatial domain inversions from months to hours or less. Using isothermal remanent magnetization measurements of multiple synthetic and natural samples, we show that the capabilities of the TNT-NN algorithm allow scans with sizes that made them previously inaccesible to NNLS techniques to be inverted. Ultimately, the TNT-NN algorithm enables spatial domain inversions of MM data on an accelerated timescale that renders spatial domain analyses for modern MM studies practical. In particular, this new technique enables MM experiments that would have required an impractical amount of inversion time such as high-resolution stepwise magnetization and demagnetization and 3-dimensional inversions.
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- 2019
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10. Numerical Modeling of the Effects of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling
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Mohamed Ezzat, Benjamin M. Adams, Martin O. Saar, and Daniel Vogler
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plasma pulse geo drilling ,electropulse drilling ,geothermal energy ,plasma physics ,micro-plasma modeling ,partial discharge ,Technology - 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.
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- 2021
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11. Sensitivity of Reservoir and Operational Parameters on the Energy Extraction Performance of Combined CO2-EGR–CPG Systems
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Justin Ezekiel, Diya Kumbhat, Anozie Ebigbo, Benjamin M. Adams, and Martin O. Saar
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CO2-plume geothermal (CPG) ,enhanced gas recovery (EGR) ,combined CO2-EGR–CPG system ,sensitivity analysis ,reservoir simulation ,geothermal power generation ,Technology - 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.
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- 2021
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12. Simulating Plasma Formation in Pores under Short Electric Pulses for Plasma Pulse Geo Drilling (PPGD)
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Mohamed Ezzat, Daniel Vogler, Martin O. Saar, and Benjamin M. Adams
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plasma pulse geo drilling ,electropulse drilling ,geothermal ,micro-plasma modeling ,partial discharge ,Technology - 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 and 500 kV in rock pores with a width between 10 and 100 μm. 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 μm 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.
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- 2021
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13. Deep learning based closed-loop optimization of geothermal reservoir production.
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Nanzhe Wang, Haibin Chang, Xiangzhao Kong, Martin O. Saar, and Dongxiao Zhang
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- 2022
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14. TNT: A Solver for Large Dense Least-Squares Problems that Takes Conjugate Gradient from Bad in Theory, to Good in Practice.
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Joseph M. Myre, Erich Frahm, David J. Lilja, and Martin O. Saar
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- 2018
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15. 3D non-conforming mesh model for flow in fractured porous media using Lagrange multipliers.
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Philipp Schädle, Patrick Zulian, Daniel Vogler, Sthavishtha R. Bhopalam, Maria Giuseppina Chiara Nestola, Anozie Ebigbo, Rolf Krause, and Martin O. Saar
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- 2019
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16. TNT-NN: A Fast Active Set Method for Solving Large Non-Negative Least Squares Problems.
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Joe M. Myre, Erich Frahm, David J. Lilja, and Martin O. Saar
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- 2017
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17. Accelerated reactive transport simulations in heterogeneous porous medium using Reaktoro and Firedrake.
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Svetlana Kyas, Diego Tavares Volpatto, Martin O. Saar, and Allan M. M. Leal
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- 2020
18. Novel Directional Steel Shot Drilling Technology for Short-Radius Multilaterals – Field Application and Commercial Impact
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Andreas Reinicke, Paromita Deb, Martin O. Saar, Vedran Zikovic, V., Erich Lassnig, Marcel Knebel, and Jan Jette Blangé
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Reliable delivery of economic well performance of geothermal projects is affected to a high degree by uncertain reservoir quality. Construction of multilateral wells is well known as an effective concept to overcome the challenges of reservoir heterogeneity or low permeability by increasing the reservoir contact. However, the drilling costs for these structures are currently very high and multilateral well construction with standard rotary steerable systems is complex. Canopus’ directional steel shot drilling system (DSSD) has the potential to enable the construction of short-radius multilaterals at rates attractive for geothermal applications.As part of the European GEOTHERMICA project ‘DEPLOI the HEAT’, the operational performance and economic impact of Canopus’ DSSD system will be investigated. Full-scale tests at TNO’s Rijswijk Centre for Sustainable Geo-Energy (RCSG) and a field trial at the Hagerbach underground test facility (VSH) are planned for the first project year. The RCSG drilling rig enables full factory acceptance testing (FAT) of the drilling assembly before the trial at the VSH site is executed. The geology at the VSH site reflects conditions of typical mid-depth fractured limestone reservoirs in Switzerland and elsewhere. At VSH, a complete set of operational parameters and system longevity will be tested with a full-scale trial to prepare for live well deployment.Further, a techno-economic assessment of multilateral structures drilled with Canopus’ DSSD system will highlight the potential for increasing or safe-guarding well productivity and economically de-risking geothermal projects. Several operators are involved in this project and the techno-economic assessment of the drilling technology will be based on several site-specific data sets provided by them. Stochastic modeling approaches will be implemented to generate an ensemble of equally probable realizations of permeable structures in the subsurface. Then, the performance and costs of different well geometries and multilateral configurations in different subsurface model realizations will be evaluated and compared.The current status of this project will be presented with a focus on the factory acceptance testing at TNO, the VSH trial preparations and the workflow developed for the techno-economic assessment of this innovative multilateral drilling technology.
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- 2023
19. Techno-economic analysis of Advanced Geothermal Systems (AGS)
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Adam E. Malek, Benjamin M. Adams, Edoardo Rossi, Hans O. Schiegg, and Martin O. Saar
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Renewable energy ,Advanced geothermal systems ,Electric power generation ,Renewable Energy, Sustainability and the Environment ,Geothermal energy ,Closed-loop - 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., Renewable Energy, 186, ISSN:0960-1481, ISSN:1879-0682
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- 2022
20. On Reliable Prediction of Fracture Path in Anisotropic Rocks
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Mahsa Sakha, Morteza Nejati, Ali Aminzadeh, Saeid Ghouli, Martin O. Saar, and Thomas Driesner
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Earth-Surface Processes - Published
- 2022
21. The Role of High-Permeability Inclusion on Solute Transport in a 3D-Printed Fractured Porous Medium: An LIF-PIV Integrated Study
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Xiang-Zhao Kong, Mehrdad Ahkami, Isamu Naets, and Martin O. Saar
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Laser-induced fluorescence (LIF) ,Mixing metric ,General Chemical Engineering ,Fractured porous media ,Particle image velocimetry (PIV) ,3D printing ,Temporal and spatial moments ,Catalysis - 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., Transport in Porous Media, 1 (283), ISSN:0169-3913, ISSN:1573-1634, 146
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- 2023
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22. The interplay of rifting, magmatism and formation of geothermal resources in the Ethiopian Rift constrained by 3-D magnetotelluric imaging
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Marie Luise Texas Dambly, Friedemann Samrock, Alexander Grayver, and Martin O. Saar
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- 2022
23. Accelerating Lattice Boltzmann Fluid Flow Simulations Using Graphics Processors.
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Peter Bailey, Joe Myre, Stuart D. C. Walsh, David J. Lilja, and Martin O. Saar
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- 2009
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24. Permeability evolution during pressure-controlled shear slip in saw-cut and natural granite fractures
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Zhiqiang Li, Xiaodong Ma, Xiang-Zhao Kong, Martin O. Saar, and Daniel Vogler
- Published
- 2023
25. Review: Induced Seismicity During Geoenergy Development—A Hydromechanical Perspective
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SHEMIN GE and Martin O. Saar
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Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Earth and Planetary Sciences (miscellaneous) - Published
- 2022
26. Modelling Potential Geological CO2 Storage Combined with CO2-Plume Geothermal CPG Energy Extraction in Switzerland
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Kevin P. Hau, Federico Games, Rodolphe Lathion, and Martin O. Saar
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For many CO2-emitting industrial sectors, such as the cement and chemical industry, Carbon, Capture and Storage (CCS) will be necessary to reach any set climate target. CCS on its own is a very cost-intensive technology. Instead of considering CO2 as a waste to be disposed of, we propose to consider CO2 as a resource. The utilisation of CO2 in so-called CO2 Plume Geothermal (CPG) systems generates revenue by extracting geothermal energy, while permanently storing CO2 in the geological subsurface.To the best of our knowledge, this pioneer investigation is the first CCUS simulation feasibility study in Switzerland. Among others, we investigated the concept of injecting and circulating CO2 for geothermal power generation purposes from potential CO2 storage formations (saline reservoirs) in the Western part of the Swiss Molasse Basin ("Muschelkalk" and "Buntsandstein" formation).Old 2D-seismic data indicates a potential anticline structure in proximity of the Eclépens heat anomaly. Essentially, this conceptual study helps assessing it's potential CO2 storage capacity range and will be beneficial for future economical assessments. The interpretation of the intersected 2D seismic profiles reveals an apparent anticline structure that was integrated on a geological model with a footprint of 4.35 × 4.05 km2.For studying the dynamic reservoir behaviour during the CO2 circulation, we considered: (1) the petrophysical rock properties uncertainty range, (2) the injection and physics of a two-phase (CO2 and brine) fluid system, including the relative permeability characterisation, fluid model composition, the residual and solubility CO2 trapping, and (3) the thermophysical properties of resident-formation brine and the injected CO2 gas.Our study represents a first-order estimation of the expected CO2 storage capacity range at a possible anticline structure in two potential Triassic reservoir formations in the Western part of the Swiss Molasse Basin. Additionally, we assessed the effect of different well locations on CO2 injection operations.Our currently still-ongoing study will investigate production rates and resulting well flow regimes in a conceptual CO2 production well for geothermal energy production in the future. Nonetheless, our preliminary results indicate that, under ideal conditions, both reservoirs combined can store more than 8 Mt of CO2 over multiple decades of CCUS operation. From our results, we can clearly identify limiting factors on the overall storage capacity, such as for example the reservoir fluid pressure distribution and well operation constraints.
- Published
- 2022
27. Performance analysis of single-phase, multiphase, and multicomponent lattice-Boltzmann fluid flow simulations on GPU clusters.
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Joe Myre, Stuart D. C. Walsh, David J. Lilja, and Martin O. Saar
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- 2011
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28. A new partial-bounceback lattice-Boltzmann method for fluid flow through heterogeneous media.
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Stuart D. C. Walsh, Holly Burwinkle, and Martin O. Saar
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- 2009
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29. Accelerating geoscience and engineering system simulations on graphics hardware.
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Stuart D. C. Walsh, Martin O. Saar, Peter Bailey, and David J. Lilja
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- 2009
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30. Mode I fracture growth in anisotropic rocks: Theory and experiment
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Florian Amann, Morteza Nejati, Thomas Driesner, Martin O. Saar, and Ali Aminzadeh
- Subjects
Strain energy release rate ,Materials science ,Applied Mathematics ,Mechanical Engineering ,Strain energy density function ,Geometry ,Condensed Matter Physics ,Physics::Geophysics ,Fracture toughness ,Mechanics of Materials ,Bed ,Modeling and Simulation ,Foliation (geology) ,Fracture (geology) ,General Materials Science ,Sedimentary rock ,Anisotropy - Abstract
This paper presents the results of 124 pure Mode I fracture toughness tests on two types of anisotropic rocks, the metamorphic Grimsel Granite and the sedimentary Mont Terri Opalinus Clay. The results show that Mode I cracks in anisotropic rocks tend to kink towards the foliation or bedding planes that are weaker in strength. The experiment data for kink angle and apparent fracture toughness are compared to the predictions of three well-known crack growth criteria: the maximum tangential stress (MTS), the maximum energy release rate (MERR), and the minimum (maximum in anisotropic materials) strain energy density (MSED). All these criteria overestimate the kink angle, while underestimating the apparent fracture toughness. The MTS yields predictions that are closest to the experiment data, while the MSED predictions are the furthest. We also show that the inclusion of the T-stress into the MTS criterion improves the predictions of the fracture growth. This indicates that the T-stress can play a significant role in the Mode I fracture growth of anisotropic rocks.
- Published
- 2020
31. Accelerating Reactive Transport Modeling: On-Demand Machine Learning Algorithm for Chemical Equilibrium Calculations
- Author
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Martin O. Saar, Dmitrii A. Kulik, Allan M.M. Leal, and Svetlana Kyas
- Subjects
Computer science ,business.industry ,General Chemical Engineering ,Computation ,0208 environmental biotechnology ,02 engineering and technology ,010502 geochemistry & geophysics ,Machine learning ,computer.software_genre ,01 natural sciences ,Catalysis ,020801 environmental engineering ,Nonlinear system ,Heat transfer ,Fluid dynamics ,Polygon mesh ,Artificial intelligence ,Chemical equilibrium ,business ,Reactive system ,computer ,Algorithm ,Order of magnitude ,0105 earth and related environmental sciences - Abstract
During reactive transport modeling, the computing cost associated with chemical equilibrium calculations can be 10 to 10,000 times higher than that of fluid flow, heat transfer, and species transport computations. These calculations are performed at least once per mesh cell and once per time step, amounting to billions of them throughout the simulation employing high-resolution meshes. To radically reduce the computing cost of chemical equilibrium calculations (each requiring an iterative solution of a system of nonlinear equations), we consider an on-demand machine learning algorithm that enables quick and accurate prediction of new chemical equilibrium states using the results of previously solved chemical equilibrium problems within the same reactive transport simulation. The training operations occur on-demand, rather than before the start of the simulation when it is not clear how many training points are needed to accurately and reliably predict all possible chemical conditions that may occur during the simulation. Each on-demand training operation consists of fully solving the equilibrium problem and storing some key information about the just computed chemical equilibrium state (which is used subsequently to rapidly predict similar states whenever possible). We study the performance of the on-demand learning algorithm, which is mass conservative by construction, by applying it to a reactive transport modeling example and achieve a speed-up of one or two orders of magnitude (depending on the activity model used). The implementation and numerical tests are carried out in Reaktoro (reaktoro.org), a unified open-source framework for modeling chemically reactive systems.
- Published
- 2020
32. Simulation of rock failure modes in thermal spallation drilling
- Author
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Daniel Vogler, Stuart D.C. Walsh, Martin O. Saar, and Philipp Rudolf von Rohr
- Subjects
Jet (fluid) ,010102 general mathematics ,0211 other engineering and technologies ,Borehole ,Drilling ,02 engineering and technology ,Mechanics ,Geotechnical Engineering and Engineering Geology ,Spall ,01 natural sciences ,Rise time ,Thermal ,Earth and Planetary Sciences (miscellaneous) ,Spallation ,0101 mathematics ,Rock failure ,Geology ,021101 geological & geomatics engineering - Abstract
Thermal spallation drilling is a contact-less means of borehole excavation that works by exposing a rock surface to a high-temperature jet flame. In this study, we investigate crucial factors for the success of such thermal drilling operations using numerical simulations of the thermomechanical processes leading to rock failure at the borehole surface. To that end, we integrate a model developed for spalling failure with our thermomechanical simulations. In particular, we consider the role of material heterogeneities, maximum jet-flame temperature and maximum jet-flame temperature rise time on the onset of inelastic deformation and subsequent damage. We further investigate differences in energy consumption for the studied system configurations. The simulations highlight the importance of material composition, as thermal spallation is favored in fine-grained material with strong material heterogeneity. The model is used to test the relationship between the jet-flame temperature and the onset of thermal spallation.
- Published
- 2020
33. A lattice-Boltzmann study of permeability-porosity relationships and mineral precipitation patterns in fractured porous media
- Author
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Andrea Parmigiani, Mehrdad Ahkami, Xiang-Zhao Kong, Paolo Roberto Di Palma, and Martin O. Saar
- Subjects
Materials science ,Advection ,Lattice Boltzmann methods ,Soil science ,010103 numerical & computational mathematics ,Thermal diffusivity ,01 natural sciences ,Computer Science Applications ,Reaction rate ,Computational Mathematics ,Permeability (earth sciences) ,Computational Theory and Mathematics ,Fluid dynamics ,0101 mathematics ,Computers in Earth Sciences ,Porous medium ,Porosity - Abstract
Mineral precipitation can drastically alter a reservoir’s ability to transmit mass and energy during various engineering/natural subsurface processes, such as geothermal energy extraction and geological carbon dioxide sequestration. However, it is still challenging to explain the relationships among permeability, porosity, and precipitation patterns in reservoirs, particularly in fracture-dominated reservoirs. Here, we investigate the pore-scale behavior of single-species mineral precipitation reactions in a fractured porous medium, using a phase field lattice-Boltzmann method. Parallel to the main flow direction, the medium is divided into two halves, one with a low-permeability matrix and one with a high-permeability matrix. Each matrix contains one flow-through and one dead-end fracture. A wide range of species diffusivity and reaction rates is explored to cover regimes from advection- to diffusion-dominated, and from transport- to reaction-limited. By employing the ratio of the Damkohler (Da) and the Peclet (Pe) number, four distinct precipitation patterns can be identified, namely (1) no precipitation (Da/Pe 100), (3) fracture isolation (1 1), and (4) diffusive precipitation (1 < Da/Pe
- Published
- 2020
34. Analytical Approaches for Porous Media Geothermal Power Calculations
- Author
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Daniel T. Birdsell, Benjamin M. Adams, Jonathan D. Ogland-Hand, Jeffrey M. Bielicki, Mark R. Fleming, and Martin O. Saar
- Abstract
Geothermal electricity generation may play a role in reducing greenhouse gas emissions and addressing climate change in a cost-effective manner. Reservoir equations for pressure and temperature must be coupled to a power cycle model to calculate electricity generation from a geothermal power plant. This work focuses on sedimentary basin geothermal power production, which relies on flow through porous and permeable aquifers in sedimentary basins. Previous work has used numerical reservoir simulators, but we introduce analytical reservoir solutions for reservoir impedance, wellbore heat loss, and reservoir heat depletion in this work. The reservoir impedance and wellbore heat loss solutions are combined with a power cycle model to calculate electricity generation. The reservoir heat depletion solution provides insight into the reservoir lifetime because electricity generation decreases with reservoir temperature. We compare the analytical and numerical approaches and discuss their implications for geothermal electricity generation from sedimentary basins. Both approaches have merits, and the comparison herein can guide those who want to understand geothermal electricity production.
- Published
- 2022
35. Shear induced fluid flow path evolution in rough-wall fractures : A particle image velocimetry examination
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Isamu Naets, Mehrdad Ahkami, Po-Wei Huang, Martin O. Saar, and Xiang-Zhao Kong
- Subjects
ddc:690 ,Water Science and Technology - Abstract
Journal of hydrology 610, 127793 (2022). doi:10.1016/j.jhydrol.2022.127793, Published by Elsevier, Amsterdam [u.a.]
- Published
- 2022
36. Flexible CO2-plume geothermal (CPG-F): Using geologically stored CO2 to provide dispatchable power and energy storage
- Author
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Mark R. Fleming, Benjamin M. Adams, Jonathan D. Ogland-Hand, Jeffrey M. Bielicki, Thomas H. Kuehn, and Martin O. Saar
- Subjects
Renewable energy ,Fuel Technology ,Carbon dioxide ,Geothermal energy ,Carbon Dioxide Plume Geothermal (CPG) ,Large-scale energy storage ,Operational Strategies ,Nuclear Energy and Engineering ,Renewable Energy, Sustainability and the Environment ,Energy Engineering and Power Technology - 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 h (8 h-16 h 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., Energy Conversion and Management, 253, ISSN:0196-8904, ISSN:1879-2227
- Published
- 2022
- Full Text
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37. Plasma Pulse Geo-Drilling as a Low-cost Drilling Technology for Deep-geothermal Energy Utilization: Status and Challenges
- Author
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Mohamed Ezzat, Jascha Börner, Daniel Vogler, Volker Wittig, and Martin O. Saar
- Abstract
Geothermal energy can be a limitless and CO2-free energy resource. However, moderate geothermal temperature gradients of ∼30 oC/km in most regions typically require employing so-called "Advanced" or "Enhanced" geothermal systems, called AGS and EGS, respectively, which require reservoirs with temperatures >150 oC. To access such high temperatures, we need to drill deeper than 5 km, i.e., in hard rock. The costs of drilling to such depths, using traditional rotary drilling, increase exponentially with depth and can be up to 80% of the total geothermal project investment. These high drilling costs can be reduced significantly with contactless drilling technologies (e.g., thermal spallation drilling, laser drilling, microwave drilling, and Plasma Pulse Geo-Drilling), as they avoid the lengthy tripping times associated with drill-bit damage. PPGD uses high-voltage pulses of a few microseconds duration to fracture the rock, thereby drilling without any mechanical abrasion. Future PPGD costs may be as low as 10% of mechanical rotary drilling costs (Schiegg et al., 2015). Our PPGD research addresses two outstanding questions: (1) Understand the fundamental physics of the electric breakdown inside the rock and associated rock fracturing processes, which we investigate numerically (Ezzat et al., 2022, 2021; Vogler et al., 2020; Walsh and Vogler, 2020). (2) Evaluate the PPGD performance under deep-wellbore conditions of ~5 km (i.e., high pore and lithostatic pressures, and high temperatures). Our ongoing numerical and experimental studies are expected to provide further insights into the applicability of PPGD for geothermal energy utilization. First, we numerically model the formation of a plasma in rock pores, which constitutes the onset of rock failure during the PPGD process. These numerical models show the significant effect of the pore characteristics on the PPGD process and give insight into how future PPGD operations should be designed. Second, we conduct PPGD physical experiments, where we employ lithostatic pressures of up to 1500 bar, pore pressures of up to 500 bar, temperatures of up to 80 oC, and voltages of up to 300 kV. Concluding these experiments with the associated challenges shall demonstrate whether PPGD is efficient at great depths of up to 5 km. Combining our numerical and experimental results allows optimizing future PPGD operations., EGUsphere
- Published
- 2022
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38. Correction to: Relating Darcy-Scale Chemical Reaction Order to Pore-Scale Spatial Heterogeneity
- Author
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Po-Wei Huang, Bernd Flemisch, Chao-Zhong Qin, Martin O. Saar, and Anozie Ebigbo
- Subjects
General Chemical Engineering ,Catalysis - Abstract
Transport in Porous Media, ISSN:0169-3913, ISSN:1573-1634
- Published
- 2022
- Full Text
- View/download PDF
39. On the validation of mixed-mode I/II crack growth theories for anisotropic rocks
- Author
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Mahsa Sakha, Morteza Nejati, Ali Aminzadeh, Saeid Ghouli, Martin O. Saar, and Thomas Driesner
- Subjects
Anisotropic rock ,Maximum energy release rate ,Mechanics of Materials ,Applied Mathematics ,Mechanical Engineering ,Modeling and Simulation ,Maximum tangential stress ,Fracture growth ,Maximum strain energy density ,General Materials Science ,Condensed Matter Physics - Abstract
We evaluate the accuracy of three well-known fracture growth theories to predict crack trajectories in anisotropic rocks through comparison with new experimental data. The results of 99 fracture toughness tests on the metamorphic Grimsel Granite under four different ratios of mixed-mode I/II loadings are reported. For each ratio, the influence of the anisotropy orientation on the direction of fracture growth is also analyzed. Our results show that for certain loading configurations, the anisotropy offsets the loading influence in determining the direction of crack growth, whereas in other configurations, these factors reinforce each other. To evaluate the accuracy of the fracture growth theories, we compare the experiment results for the kink angle and the effective fracture toughness with the predictions of the maximum tangential stress (MTS), the maximum energy release rate (MERR), and the maximum strain energy density (MSED) criteria. The criteria are first assessed in their classical forms employed in the literature. It is demonstrated that the energy-based criteria in their classical formulation cannot yield good predictions. We then present modified forms of the ERR and SED functions in which the tensile and shear components are decomposed. These modified forms give significantly better predictions of fracture growth paths. The evaluation of the three criteria illustrates that the modified MSED criterion is the least accurate model even in the modified form, while the results predicted by MTS and modified MERR are well matched with the experimental results., International Journal of Solids and Structures, 241, ISSN:0020-7683, ISSN:1879-2146
- Published
- 2022
- Full Text
- View/download PDF
40. On the applicability of connectivity metrics to rough fractures under normal stress
- Author
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Hoda Javanmard, Martin O. Saar, and Daniel Vogler
- Subjects
Connectivity ,Rough fractures ,Permeability ,Percolation theory ,Water Science and Technology ,Physics::Geophysics - 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 Θ 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., Advances in Water Resources, 161, ISSN:0309-1708, ISSN:1872-9657
- Published
- 2022
- Full Text
- View/download PDF
41. Numerical analysis and optimization of the performance of CO2-Plume Geothermal (CPG) production wells and implications for electric power generation
- Author
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Benjamin M. Adams, Justin Ezekiel, Anozie Ebigbo, and Martin O. Saar
- Subjects
Petroleum engineering ,Power station ,Renewable Energy, Sustainability and the Environment ,Water flow ,Flow (psychology) ,Borehole ,Geology ,Geotechnical Engineering and Engineering Geology ,Electricity generation ,Drawdown (hydrology) ,Environmental science ,Electric power ,Relative permeability ,CO2-plume geothermal ,Production well ,Wellbore flow regimes ,Numerical modeling ,Power generation ,CO2 capture utilization and storage (CCUS) - 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, admissible 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 production well and to maximize CPG electric power output. ISSN:0375-6505
- Published
- 2022
42. Numerical Modeling of the Effects of Pore Characteristics on the Electric Breakdown of Rock for Plasma Pulse Geo Drilling
- Author
-
Mohamed Ezzat, Benjamin M. Adams, Martin O. Saar, and Daniel Vogler
- Subjects
Technology ,plasma pulse geo drilling ,Partial discharge ,Electropulse drilling ,Micro-plasma modeling ,High-voltage pulses ,Plasma puls geo drilling ,Geothermal energy ,Plasma physics ,Electric breakdown - 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., Energies, 15 (1), ISSN:1996-1073
- Published
- 2022
- Full Text
- View/download PDF
43. A methodology to determine the elastic properties of anisotropic rocks from a single uniaxial compression test
- Author
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Marie Luise Texas Dambly, Martin O. Saar, and Morteza Nejati
- Subjects
Seismic anisotropy ,Uniaxial compression ,Materials science ,Explicit formulae ,Granite ,0211 other engineering and technologies ,Young's modulus ,02 engineering and technology ,010502 geochemistry & geophysics ,Elastic constants ,01 natural sciences ,symbols.namesake ,lcsh:Engineering geology. Rock mechanics. Soil mechanics. Underground construction ,Transverse isotropy ,Transversely isotropic rock ,Young’s modulus ,Poisson’s ratio ,Anisotropy ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Mathematical analysis ,Tangent ,Geotechnical Engineering and Engineering Geology ,Poisson's ratio ,Nonlinear system ,lcsh:TA703-712 ,symbols - Abstract
This paper introduces a new methodology to measure the elastic constants of transversely isotropic rocks from a single uniaxial compression test. We first give the mathematical proof that a uniaxial compression test provides only four independent strain equations. As a result, the exact determination of all five independent elastic constants from only one test is not possible. An approximate determination of the Young’s moduli and the Poisson’s ratios is however practical and efficient when adding the Saint-Venant relation as the fifth equation. Explicit formulae are then developed to calculate both secant and tangent definitions of the five elastic constants from a minimum of four strain measurements. The results of this new methodology applied on three granitic samples demonstrate a significant stress-induced nonlinear behavior, where the tangent moduli increase by a factor of three to four when the rock is loaded up to 20 MPa. The static elastic constants obtained from the uniaxial compression test are also found to be significantly smaller than the dynamic ones obtained from the ultrasonic measurements., Journal of Rock Mechanics and Geotechnical Engineering, 11 (6), ISSN:1674-7755, ISSN:2589-0417
- Published
- 2019
44. Benchmark study of simulators for thermo-hydraulic modelling of low enthalpy geothermal processes
- Author
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Stijn Beernink, Peter Alt-Epping, Carsten M. Nielsen, Antoine Armandine Les Landes, Daniel Traver Birdsell, Thomas Driesner, Marc Perreaux, Martin O. Saar, Virginie Hamm, Julian Mindel, Sebastià Olivella, Daniela Van den Heuvel, Maarten W. Saaltink, Martin Bloemendal, Simon Lopez, Charles Maragna, Rubén Vidal, Universitat Politècnica de Catalunya. Departament d'Enginyeria Civil i Ambiental, Universitat Politècnica de Catalunya. Doctorat en Enginyeria del Terreny, Universitat Politècnica de Catalunya. MSR - Mecànica del Sòls i de les Roques, and Universitat Politècnica de Catalunya. GHS - Grup d'Hidrologia Subterrània
- Subjects
Discretization ,Geothermal resources ,Renewable Energy, Sustainability and the Environment ,Computer science ,Geology ,Geotechnical Engineering and Engineering Geology ,Energia geotèrmica ,Set (abstract data type) ,Test case ,Compass ,Energies::Energia geotèrmica [Àrees temàtiques de la UPC] ,Benchmark (computing) ,Range (statistics) ,Enginyeria civil::Geotècnia::Mecànica de sòls [Àrees temàtiques de la UPC] ,Geothermal gradient ,Simulation ,Eclipse - Abstract
In order to assess the thermo-hydraulic modelling capabilities of various geothermal simulators, a comparative test suite was created, consisting of a set of cases designed with conditions relevant to the low-enthalpy range of geothermal operations within the European HEATSTORE research project. In an effort to increase confidence in the usage of each simulator, the suite was used as a benchmark by a set of 10 simulators of diverse origin, formulation, and licensing characteristics: COMSOL, MARTHE, ComPASS, Nexus-CSMP++, MOOSE, SEAWATv4, CODE_BRIGHT, Tough3, PFLOTRAN, and Eclipse 100. The synthetic test cases (TCs) consist of a transient pressure test verification (TC1), a well-test comparison (TC2), a thermal transport experiment validation (TC3), and a convection onset comparison (TC4), chosen to represent well-defined subsets of the coupled physical processes acting in subsurface geothermal operations. The results from the four test cases were compared among the participants, to known analytical solutions, and to experimental measurements where applicable, to establish them as reference expectations for future studies. A basic description, problem specification, and corresponding results are presented and discussed. Most participating simulators were able to perform most tests reliably at a level of accuracy that is considered sufficient for application to modelling tasks in real geothermal projects. Significant relative deviations from the reference solutions occurred where strong, sudden (e.g. initial) gradients affected the accuracy of the numerical discretization, but also due to sub-optimal model setup caused by simulator limitations (e.g. providing an equation of state for water properties)., Geothermics, 96, ISSN:0375-6505
- Published
- 2021
45. DBCreate: A SUPCRT92-based program for producing EQ3/6, TOUGHREACT, and GWB thermodynamic databases at user-defined T and P.
- Author
-
Xiang-Zhao Kong, Benjamin M. Tutolo, and Martin O. Saar
- Published
- 2013
- Full Text
- View/download PDF
46. Multi-disciplinary characterizations of the Bedretto Lab – a unique underground geoscience research facility
- Author
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Hannes Krietsch, Linus Villiger, Francisco Seberto, Domenico Giardini, Morteza Nejati, Marian Hertrich, Philipp Kästli, Hansruedi Maurer, Valentin Gischig, Rebecca Hochreutener, Anne Obermann, Raymi Castilla, Alba Zappone, Stefan Wiemer, Michèle Marti, Antonio Pio Rinaldi, Xiaodong Ma, Barbara Nägeli, Martin O. Saar, Thomas Driesner, Falko Bethmann, Kai Bröker, Quinn Wenning, Peter Meier, Alexis Shakas, Katrin Plenkers, Simon Löw, Nima Gholizadeh Doonechaly, and Florian Amann
- Subjects
Current (stream) ,Overburden ,Feature (archaeology) ,Borehole ,Induced seismicity ,Petrology ,Rock mass classification ,Geothermal gradient ,Geology ,Waste disposal - Abstract
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., Solid Earth Discussions, ISSN:1869-9537
- Published
- 2021
47. Simulating Plasma Formation in Pores under Short Electric Pulses for Plasma Pulse Geo Drilling (PPGD)
- Author
-
Adams, Mohamed Ezzat, Daniel Vogler, Martin O. Saar, and Benjamin M.
- Subjects
plasma pulse geo drilling ,electropulse drilling ,geothermal ,micro-plasma modeling ,partial discharge - 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 and 500 kV in rock pores with a width between 10 and 100 μm. 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 μm 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.
- Published
- 2021
- Full Text
- View/download PDF
48. Heat depletion in sedimentary basins and its effect on the design and electric power output of CO2 Plume Geothermal (CPG) systems
- Author
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Nagasree Garapati, Daniel Vogler, Martin O. Saar, Jeffrey M. Bielicki, Thomas H. Kuehn, and Benjamin M. Adams
- Subjects
geography ,geography.geographical_feature_category ,060102 archaeology ,Renewable Energy, Sustainability and the Environment ,business.industry ,020209 energy ,Geothermal heating ,06 humanities and the arts ,02 engineering and technology ,Sedimentary basin ,Plume ,Permeability (earth sciences) ,Electricity generation ,0202 electrical engineering, electronic engineering, information engineering ,Environmental science ,0601 history and archaeology ,Electric power ,Electricity ,Petrology ,business ,Geothermal gradient - 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., Renewable Energy, 172, ISSN:0960-1481, ISSN:1879-0682
- Published
- 2021
49. Modified semi-circular bend test to determine the fracture toughness of anisotropic rocks
- Author
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Ali Aminzadeh, Morteza Nejati, Martin O. Saar, and Thomas Driesner
- Subjects
Materials science ,Mechanical Engineering ,0211 other engineering and technologies ,Modulus ,02 engineering and technology ,Finite element method ,Shear modulus ,020303 mechanical engineering & transports ,Fracture toughness ,0203 mechanical engineering ,Mechanics of Materials ,Orientation (geometry) ,General Materials Science ,Composite material ,Anisotropy ,Stress intensity factor ,021101 geological & geomatics engineering ,Dimensionless quantity - Abstract
The conventional semi-circular bend (SCB) test of anisotropic rocks, with symmetric loading, generates a Mixed-Mode I / II crack tip loading when the crack is not aligned with one of the principal material directions. This paper presents a modified SCB test for anisotropic rocks to ensure a pure Mode I crack tip loading. It is demonstrated that the stress intensity factor (SIF) solution of an anisotropic SCB specimen depends on two dimensionless parameters, the anisotropy ratios of the Young’s modulus and apparent shear modulus, as well as the anisotropy orientation. These two dimensionless parameters are selected since they have physical meaning, and are generally bounded for rock materials. Based on these anisotropy parameters, the semi-circular test is modified to configure pure Mode I , or tensile stress at the crack tip, by using an asymmetric three-point bend configuration. Extensive finite element analyses are performed to obtain the span ratio and normalized SIF of the SCB specimen with different anisotropy ratios and orientations.
- Published
- 2019
50. The value of bulk energy storage for reducing CO2 emissions and water requirements from regional electricity systems
- Author
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Thomas A. Buscheck, Benjamin M. Adams, Yaoping Wang, Jeffrey M. Bielicki, Martin O. Saar, and Jonathan D. Ogland-Hand
- Subjects
Pumped-storage hydroelectricity ,Wind power ,Compressed air energy storage ,Renewable Energy, Sustainability and the Environment ,business.industry ,020209 energy ,Environmental engineering ,Energy Engineering and Power Technology ,02 engineering and technology ,Nuclear power ,Energy storage ,Fuel Technology ,Variable renewable energy ,020401 chemical engineering ,Nuclear Energy and Engineering ,Natural gas ,0202 electrical engineering, electronic engineering, information engineering ,Environmental science ,Electricity ,0204 chemical engineering ,business - Abstract
The implementation of bulk energy storage (BES) technologies can help to achieve higher penetration and utilization of variable renewable energy technologies (e.g., wind and solar), but it can also alter the dispatch order in regional electricity systems in other ways. These changes to the dispatch order affect the total amount of carbon dioxide (CO2) that is emitted to the atmosphere and the amount of total water that is required by the electricity generating facilities. In a case study of the Electricity Reliability Council of Texas system, we separately investigated the value that three BES technologies (CO2-Geothermal Bulk Energy Storage, Compressed Air Energy Storage, Pumped Hydro Energy Storage) could have for reducing system-wide CO2 emissions and water requirements. In addition to increasing the utilization of wind power capacity, the dispatch of BES also led to an increase in the utilization of natural gas power capacity and of coal power capacity, and a decrease in the utilization of nuclear power capacity, depending on the character of the net load, the CO2 price, the water price, and the BES technology. These changes to the dispatch order provided positive value (e.g., increase in natural gas generally reduced CO2 emissions; decrease in nuclear utilization always decreased water requirements) or negative value (e.g., increase in coal sometimes increased CO2 emissions; increase in natural gas sometimes increased water requirements) to the regional electricity system. We also found that these values to the system can be greater than the cost of operating the BES facility. At present, there are mechanisms to compensate BES facilities for ancillary grid services, and our results suggest that similar mechanisms could be enacted to compensate BES facilities for their contribution to the environmental sustainability of the system.
- Published
- 2019
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