BUSCADOR RECOLECTA

Many countries have assigned an indispensable role for carbon capture and storage (CCS) in their national climate change mitigation pathways. However, CCS deployment has stalled in most countries with only limited commercial projects realised mainly in hydrocarbon-rich countries for enhanced oil recovery. If the Paris Agreement is to be met, then this progress must be replicated widely, including hydrocarbon-limited countries. In this study, we present a novel source-to-sink assessment methodology based on a hubs and clusters approach to identify favourable regions for CCS deployment and attract renewed public and political interest in viable deployment pathways. Here, we apply this methodology to Spain, where fifteen emission hubs from both the power and the hard-to-abate industrial sectors are identified as potential CO2 sources. A priority storage structure and two reserves for each hub are selected based on screening and ranking processes using a multi-criteria decision-making method. The priority source-to-sink clusters are identified indicating four potential development regions, with the North-Western and North-Eastern Spain recognised as priority regions due to resilience provided by different types of CO2 sources and geological structures. Up to 68.7 Mt CO2 per year, comprising around 21% of Spanish emissions can be connected to clusters linked to feasible storage. CCS, especially in the hard-to-abate sector, and in combination with other low-carbon energies (e.g., blue hydrogen and bioenergy), remains a significant and unavoidable contributor to the Paris Agreement's mid-century net-zero target. This study shows that the hubs and clusters approach can facilitate CCS deployment in Spain and other hydrocarbon-limited countries.

Geo-energy applications such as geologic carbon storage, geothermal energy extraction, and subsurface energy storage, imply fluid injection and production resulting in
pressure and temperature diffusion. Consequent changes in the initial hydraulic and thermal state may induce seismicity, usually nucleated at faults that cross the injection
formation. Through fully coupled hydro-mechanical simulations, we investigate the fault stability affected by fluid injection into a porous aquifer that is overlaid and underlain by
low permeable clay-rich formations. We find that aquifer pressurization as a result of fluid injection causes significant stress changes around the fault. Simulation
results show that the least stable situation occurs at the contact between the aquifer and the fault damage zone – unexpectedly not within the fault. Induced earthquakes are
likely to nucleate on the edge of the fault damage zone, leading to a lateral growth of the damage zone and a possible spreading of the fault zone., V.V. would like to acknowledge funding from the
European Research Council (ERC) under European
Union’s Horizon 2020 research and innovation
programme (grant agreement No 801809), Peer reviewed

Forecasting and mitigating induced seismicity requires understanding of the underlying physical processes. Poromechanical and thermal
effects on stresses and shear slip stress transfer play a non-negligible role that has challenged the classical interpretation in which induced
seismicity is caused exclusively by pressure buildup (De Simone et al., 2017). In this contribution, we analyze how the stress changes induced as
a result of fluid injection affect fault stability. We perform fully coupled hydro-mechanical simulations of fluid injection into a saline aquifer
bounded above and below by low-permeable clay-rich rock and intersected by a low-permeable steep fault. Simulation results show that
maintaining a constant injection rate leads to a progressive reservoir pressurization on the side of the fault where injection takes place (Fig.
1a). Given the low-permeability of the fault core, pressure buildup is negligible on the other side of the fault. These pore pressure changes
cause strong variations in the total stresses controlled by rock stiffness around the fault. Deviatoric stress changes are controlled by stress
balance from the two sides of the fault: the upper part of the reservoir, juxtaposed to the stiffer reservoir on the right, has a lower increase in the
deviatoric stress than the lower part, which is juxtaposed to the more compliant caprock. This implies increased fault stability in the upper part and
decreased fault stability in the lower part (Fig, 1d). As highlighted by our results, fault stability is: i) non-homogeneous within the whole fault
and ii) controlled by poromechanical stress changes as much as by pressure buildup., V.V. would like to acknowledge funding from the
European Research Council (ERC) under European
Union’s Horizon 2020 research and innovation
programme (grant agreement No 801809), and CSIC
through the Intramural project 201730I100, Peer reviewed

Geologic carbon storage is considered as a key technology to reach zero emissions by 2050 in order to meet the objective of the Paris Agreement of limiting temperature increase below 2 ºC. Yet, a number of concerns exist about the long-term caprock integrity to permanently storing CO2 in deep geological formations. To gain knowledge on the sealing properties of clay-rich geomaterials that serve as caprock, field experiments in underground research laboratories are required. Here, we present preliminary results of the modeling of a long-term CO2 injection experiment into Opalinus Clay (shale) at Mont Terri, Switzerland. Simulation results show that the high entry pressure hinders CO2 penetration in free phase into the shale, but CO2 does get into Opalinus Clay dissolved into the resident pore water. The presence of fractures in the caprock provide preferential paths for pressure propagation and for CO2 migration provided that the CO2 entry pressure is low enough to permit CO2 entering into it. The modeling of the experiment is ongoing in order to define the design of the experiment., VV would like to acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 801809)., Peer reviewed

Geologic carbon storage, as well as other geoenergy
applications, such as geothermal energy, seasonal natural
gas storage and subsurface energy storage imply fluid
injection and/or extraction that causes changes in rock stress
field and may induce (micro)seismicity. If felt, seismicity
has a negative effect on public perception and may jeopardize
wellbore stability and damage infrastructure. Thus, induced
earthquakes should be minimized to successfully deploy
geo-energies. However, numerous processes may trigger
induced seismicity, which contribute to making it complex
and translates into a limited forecast ability of current
predictive models.We review the triggering mechanisms
of induced seismicity. Specifically, we analyze (1) the impact
of pore pressure evolution and the effect that properties
of the injected fluid have on fracture and/or fault stability;
(2) non-isothermal effects caused by the fact that the injected
fluid usually reaches the injection formation at a lower
temperature than that of the rock, inducing rock contraction,
thermal stress reduction and stress redistribution around the
cooled region; (3) local stress changes induced when lowpermeability
faults cross the injection formation, which may
reduce their stability and eventually cause fault reactivation;
(4) stress transfer caused by seismic or aseismic slip; and
(5) geochemical effects, which may be especially relevant
in carbonate-containing formations. We also review characterization
techniques developed by the authors to reduce the
uncertainty in rock properties and subsurface heterogeneity
both for the screening of injection sites and for the operation
of projects. Based on the review, we propose a methodology
based on proper site characterization, monitoring and pressure
management to minimize induced seismicity., Víctor Vilarrasa acknowledges funding from
the European Research Council (ERC) under the European Union’s
Horizon 2020 Research and Innovation Programme (grant agreement
no. 801809). Jonny Rutqvist acknowledges funding by the
Assistant Secretary for Fossil Energy, National Energy Technology
Laboratory, National Risk Assessment Partnership of the U.S. Department
of Energy to the Lawrence Berkeley National Laboratory
under contract no. DEAC02-05CH11231., Peer reviewed

Geothermal systems, including hydrothermal systems [1], enhanced geothermal systems (EGS) [2], and superhot or supercritical systems [3–5], are receiving an increasing interest because they provide carbon-free energy that is necessary to shift the current dependency on fossil fuels and thus significantly reduce CO2 emissions to the atmosphere [6]. Geothermal energy can potentially provide continuous energy output without daily or seasonal fluctuations—a strong advantage when compared to other renewable sources—and negative emissions if CO2 is used as the working fluid [7–9]. However, the deployment of geothermal systems is being hindered by insufficient permeability of the reservoir rock [10], excessive induced seismicity during reservoir stimulation [11], and geochemical reactions accelerated by high temperature that lead to corrosion and scaling [12].

To overcome these challenges, interdisciplinary approaches that investigate relevant processes occurring during geothermal energy exploitation are necessary. The focus of this special issue is on geomechanical aspects of geothermal systems, including coupled processes occurring in multiphase systems, experimental characterization of rock and inelastic deformation that may induce seismicity, and geochemistry of geothermal systems. This special issue compiles the most recent advances in geothermal energy and combines the complex interactions between geomechanics, fluid flow, and geochemical reactions., The guest editors thank all the authors of this special issue and their perseverance during the publication process. We also thank the many anonymous reviewers who helped to evaluate and contributed to these papers. The guest editors would also like to acknowledge their sources of funding. V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST, grant agreement No. 801809 (http://www.georest.eu). R.M. is thankful for the support provided by the UIUC-ZJU Research Collaboration program (grant # 083650). The contribution of F.P. is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—project number PA 3451/1-1., Peer reviewed

The effect of natural CO2 leakage through water wells on groundwater chemistry from alluvial aquifers of Hamadan, Iran, has been investigated through analysis of water samples from 5 springs and 19 wells. The average CO2 partial pressure in gas charged groundwater has increased about 32 times with respect to background groundwater, leading to an increase in alkalinity and in the concentration of all ions, except for SO4, and to a decrease in pH and DO. Due to a high pH buffering capacity, pH of gas charged groundwater has decreased only one unit. The increase in salinity of the gas charged groundwater cannot be attributed to in situ weathering of aquifer materials because of (1) the lack of correlation between DIC vs δ13CDIC and TDS vs pH, (2) the high concentration of SiO2 and F and (3) the 87Sr/86Sr ratio in the range from 0.7085 to 0.7118. Instead, it can be attributed to saline CO2-rich waters from deep sources, which can dissolve a variety of minerals during their migration towards the surface. Although it is not clear the role of CH4 as electron donor, the association of δ18OSO4 and δ34SSO4 with SO4 concentration suggests that sulfate reduction could occur in the environment. The salinity of Mesozoic gas-rich springs, which present higher CO2 pressure and lower pH, is five times lower than that of Cenozoic ones because of the different degrees of metamorphism, which lead to an increase in grain size and slower reaction rate in Mesozoic than in Cenozoic carbonate rocks., B.D. acknowledges the financial support received from the “Iran’s Ministry of Science, Research and Technology, Iran” (Ph.D. students’ sabbatical grants), Hamadan regional water company and Geological survey of Iran. V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), grant agreement No. 801809. The authors thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF)., Peer reviewed

This Special Issue originates from selected contributions at the International Conference on Coupled Processes in Fractured Geological Media: Observation, Modeling, and Application (CouFrac2018). CouFrac2018 has been the first CouFrac conference focusing on coupled processes in fractured media, providing a platform for international discussion, communication and networking on this emerging topic. The conference was held in Wuhan, China, between 12 and 14th of November, 2018., K.-B.M. acknowledges support from the Institute of Engineering Research, Seoul National University. J.R. acknowledges support from the U.S. Department of Energy to the Lawrence Berkeley National Laboratory under contract No. DE-AC02-05CH11231. V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST, grant agreement No. 801809 (www.georest.eu)., Peer reviewed

Geologic carbon storage is required for achieving negative CO2 emissions to deal with the climate crisis. The classical concept of CO2 storage consists in injecting CO2 in geological formations at depths greater than 800 m, where CO2 becomes a dense fluid, minimizing storage volume. Yet CO2 has a density lower than the resident brine and tends to float, challenging the widespread deployment of geologic carbon storage. Here, we propose for the first time to store CO2 in supercritical reservoirs to reduce the buoyancy‐driven leakage risk. Supercritical reservoirs are found at drilling‐reachable depth in volcanic areas, where high pressure (p > 21.8 MPa) and temperature (T > 374°C) imply CO2 is denser than water. We estimate that a CO2 storage capacity in the range of 50–500 Mt yr−1 could be achieved for every 100 injection wells. Carbon storage in supercritical reservoirs is an appealing alternative to the traditional approach., The authors acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu), grant agreement No. 801809 and the support by the Spanish Ministry of Science and Innovation (Project CEX2018‐000794‐S); F. P. acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—project number PA 3451/1‐1., Peer reviewed

Fractures control fluid flow and the coupled geomechanical response of geological media in many geo-engineering and geo-energy applications. For instance, fluid flow and deformation mainly occur along fractures in enhanced geothermal systems (EGS), underground radioactive waste repositories and CO2 storage (Rutqvist and Stephansson, 2003). Coupled thermo-hydro-mechanical (THM) processes are induced in rock masses as a result of perturbations in the pore pressure, e.g., fluid injection and production, and/or temperature, e.g., cold fluid injection and disposal of radioactive waste. One example of these coupled processes is the fracture opening as a result of pore pressure increase, which enhances fracture permeability (Tsang, 1999).
The geo-engineering and geo-energy applications of interest involve large fractured rock masses that include multiple fractures. Numerically modeling of coupled hydro-mechanical (HM) processes while considering a large number of fractures is extremely challenging (Lei et al., 2017). We propose using a continuum mechanics approach to model fractures. Before studying fractured rock masses containing many fractures, we focus on a single fracture to fully understand the hydro-mechanical behavior of a fracture to a constant injection flow rate. Here, we present some preliminary results., The authors acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809)., Peer reviewed

CO2 Long-term Periodic Injection Experiment (CO2LPIE) aims at investigating the caprock sealing capacity in geologic carbon storage in a highly monitored environment at the field scale. The experiment is carried out in the sandy facies of Opalinus Clay at the Mont Terri rock laboratory, Switzerland, to gain knowledge on the changes in the geomechanical properties induced by the geochemical reactions resulting from CO2 injection (Rebscher et al., 2019; 2020). The presence of bedding planes in Opalinus Clay is responsible for its anisotropic hydrogeological and geomechanical behavior., D.S., V.V. and I.R.K. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809). R.M. is thankful for the support from US DOE through CarbonSAFE Macon County Project DE-FE0029381., Peer reviewed

In most uses of the subsurface, especially while injecting and extracting fluids into or from a high porous reservoir rock, the existence of an overlying caprock with sufficiently low permeability is crucial for the success of the aforementioned exploitations. However, while a multitude of research has been conducted already on reservoir rocks, too little attention has been given to the equally important, sealing caprocks. As of yet, detailed studies on their behaviour on different scales in time and space are rather scarce.
The project CO2LPIE (CO2 Long-term Periodic Injection Experiment [Rebscher et al., 2019; Rebscher et al., 2020]) is committed to contribute to fill these knowledge gaps by combining an in-situ field test with CO2 injection on a time span of 15 years to 20 years. The approach is complemented with extensive geomechanical and geochemical tests in the laboratory as well as site-specific thermal, hydrological, mechanical, and chemical (THMC) computational modelling. These comprehensive investigations can significantly enhance the understanding, description, and prediction of the complex coupled processes in a caprock. Presently, the demand for factual issues are gaining more attention, as the interest in carbon capture, and storage (CCS) resurges, not the least because CCS is obtaining wider recognition as one of the necessary tools to mitigate climate change., V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu, Grant agreement No. 801809). R.M. is thankful for the support from US DOE through CarbonSAFE Macon County Project DE-FE0029381., Peer reviewed

Induced seismicity during reservoir pressurization or depletion has become a widespread issue
(Ferronato et al., 2010; Ellsworth 2013) as a result of the proliferation of geo-energy projects
(Foulger et al., 2018). Faults intersecting the injection/pumping formation undergo pore
pressure and stress changes, affecting their stability. The hydraulic properties of faults (e.g.,
permeability) control the pore pressure change which, through poromechanical effects,
increases the total stress in the rock. Faults cause additional stress change (Gheibi et al., 2017)
that is further enhanced by fault offset (Buijze et al., 2017), which can increase the frequency
of induced earthquakes. Thus, predicting the stress variation in presence of displaced faults is
particularly relevant in order to minimize the induced seismicity risk.
Analytical solutions provide accurate and fast predictions and are well suited to gain insights
into the physical mechanisms. For the problem of reservoir pressurization/depletion, Eshelby’s
inclusion theory (Eshelby, 1957) is at the heart of several existing analytical solutions that either
assume non-displaced faults (e.g., Segall, 1992; Soltanzadeh and Hawkees, 2008; Wang et al.
2016) or displaced but permeable faults (Jansen et al., 2019). Since no solution existed for lowpermeable
faults that cross the reservoir with an offset, we have developed one (Wu et al.,
2020). In this paper, we analyse the difference in terms of induced seismicity potential in
response to injection/pumping into a reservoir crossed by a displaced fault that could be either
permeable or impermeable., H.W. would like to acknowledge the financial support received from the AGAUR (Generalitat de Catalunya) through the ‘‘grant for universities and research centers for the recruitment of new research personnel (FI-2019)’’. H.W. and V.V. acknowledge financial support from the “ZoDrEx” project, which has been subsidized through the ERANET Cofund GEOTHERMICA (Project no. 731117), from the European Commission and the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) (PCI2018-093272). V.V. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu), grant agreement No. 801809. V.V. also acknowledges support by the Spanish Ministry of Science and Innovation (Project CEX2018-000794-S). F.P. acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project number PA 3451/1-1. S.D.S. acknowledges financial support from the SAD2018 project funded by the Brittany Region and from ANR LabCom Project eLabo ANR-17-LCV2-0012., Peer reviewed

Deep geological media will be intensively utilized for achieving carbon neutrality within the next few decades (Friedmann et al., 2020). Widespread deployment of geothermal energy production, geologic carbon storage, and subsurface energy storage will require massive injection and production of fluids in porous reservoir rock and fractured low permeable formations. Fluid injection and production causes pore pressure and temperature perturbations that induce deformation and stress changes (Tsang, 1991). These pressure, temperature, and stress changes affect fracture and fault stability, leading to aseismic and/or seismic slip if failure conditions are reached (Cornet et al., 1997).
Understanding how coupled processes control fluid flow and fracture stability is crucial for the success of geo-energy projects. While small shear slip, in the order of mm to cm, can be beneficial to enhance the permeability of the rock mass (Rutqvist and Stephansson, 2003), larger slip, in the order of tens of cm over rupture areas on the scale of hundred meters in diameter, may induce earthquakes that could be felt on the surface, causing nuisance to the local populations and eventually damaging structures and infrastructures (Kanamori and Brodsky, 2004). Numerical simulations of coupled processes are a useful tool to understand the interactions between pore pressure, temperatures, and stress in fractured rock as a result of fluid injection and/or extraction. In this study, we aim at identifying the long-term thermo-hydro-mechanical (THM) response of a fractured reservoir to water injection and production., V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809). R.M. is thankful for the support from US DOE through CarbonSAFE Macon County Project DE-FE0029381. F.P. acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project number PA 3451/1-1., Peer reviewed

Displaced faults crossing the reservoir could significantly increase the induced earthquake frequency in geo‐energy projects. Understanding and predicting the stress variation in such cases is essential to minimize the risk of induced seismicity. Here, we adopt the inclusion theory to develop an analytical solution for the stress response to pore pressure variations within the reservoir for both permeable and impermeable faults with offset ranging from zero to the reservoir thickness. By analyzing fault stability changes due to reservoir pressurization/depletion under different scenarios, we find that (1) the induced seismicity potential of impermeable faults is always larger than that of permeable faults under any initial and injection conditions—the maximum size of the fault undergoing failure is 3–5 times larger for impermeable than for permeable faults; (2) stress concentration at the corners results in the occurrence of reversed slip in normal faults with a normal faulting stress regime; (3) while fault offset has no impact on the slip potential for impermeable faults, the slip potential increases with the offset for permeable faults, which indicates that non‐displaced permeable faults constitute a safer choice for site selection; (4) an impermeable fault would rupture at a lower deviatoric stress, and at a smaller pressure buildup than a permeable one; and (5) the induced seismicity potential is overestimated and the injectivity underestimated if the stress arching (i.e., the poromechanical coupling) is neglected. This analytical solution is a useful tool for site selection and for supporting decision making during the lifetime of geo‐energy projects., H. Wu acknowledges the financial support received from the AGAUR (Generalitat de Catalunya) through the ‘‘grant for universities and research centers for the recruitment of new research personnel (FI‐2019)''. V. Vilarrasa acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu), Grant agreement no. 801809. V. Vilarrasa also acknowledges support by the Spanish Ministry of Science and Innovation (Project CEX2018‐000794‐S). S.D. Simone acknowledges financial support from the SAD2018 project funded by the Brittany Region and from ANR LabCom Project eLabo ANR‐17‐LCV2‐0012. M. Saaltink acknowledges financial support from the “HEATSTORE” project (170153–44011), which has been subsidized through the ERANET Cofund GEOTHERMICA (Grant agreement no. 731117), from the European Commission and the Spanish Ministry of Science, Innovation and Universities (PCI2018‐092933). F. Parisio acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—project number PA 3451/1‐1. The authors thank Tomas Aquino for his advice on the integral solutions., Peer reviewed

10 pages, 4 figures, supporting information https://doi.org/10.1029/2020GL092038.-- Data Availability Statement: The associated data is available at the repository DIGITAL.CSIC (https://digital.csic.es/handle/10261/216863, The offshore Castor Underground Gas Storage (UGS) project had to be halted after gas injection triggered three M4 earthquakes, each larger than any ever induced by UGS. The mechanisms that induced seismicity in the crystalline basement at 5–10 km depth after gas injection at 1.7 km depth remain unknown. Here, we propose a combination of mechanisms to explain the observed seismicity. First, the critically stressed Amposta fault, bounding the storage formation, crept by the superposition of well‐known overpressure effects and buoyancy of the relatively light injected gas. This aseismic slip brought an unmapped critically stressed fault in the hydraulically disconnected crystalline basement to failure. We attribute the delay between induced earthquakes to the pressure drop associated to expansion of areas where earthquakes slips cause further instabilities. Earthquakes occur only after these pressure drops have dissipated. Understanding triggering mechanisms is key to forecast induced seismicity and successfully design deep underground operations., The authors would like to acknowledge Álvaro González for sharing the catalogs that were used in Cesca et al. (2014). Funding: Víctor Vilarrasa acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (grant agreement No. 801809). Antonio Villaseñor acknowledges funding from Spanish Ministry of Science and Innovation grant CGL2017‐88864‐R. IDAEA‐CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018‐000794‐S). ICM‐CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2019‐000928‐S)., Peer reviewed

Geoenergy and geoengineering applications usually involve fluid injection into and production from fractured media. Accounting for fractures is important because of the strong poromechanical coupling that ties pore pressure changes and deformation. A possible approach to the problem uses equivalent porous media to reduce the computational cost and model complexity instead of explicitly including fractures in the models. We investigate the validity of this simplification by comparing these two approaches. Simulation results show that pore pressure distribution significantly differs between the two approaches even when both are calibrated to predict identical values at the injection and production wells. Additionally, changes in fracture stability are not well captured with the equivalent porous medium. We conclude that explicitly accounting for fractures in numerical models may be necessary under some circumstances to perform reliable coupled thermohydromechanical simulations, which could be used in conjunction with other tools for induced seismicity forecasting., A.Z. acknowledges the financial support received from the “Iran's Ministry of Science, Research and Technology” (PhD students' sabbatical grants) for visiting IDAEA‐CSIC. The contribution of F.P. is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—project number PA 3451/1‐1. R.M. is thankful for the support from US DOE through Carbon SAFE Macon County Project DE‐FE0029381. V.V. acknowledges funding from the Spanish National Research Council (CSIC) through the Intramural project 201730I100 and from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809). IDAEA‐CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018‐000794‐S). The authors declare no conflict of interest., Peer reviewed

Many countries have assigned an indispensable role for carbon capture and storage (CCS) in their national climate change mitigation pathways. However, CCS deployment has stalled in most countries with only limited commercial projects realised mainly in hydrocarbon-rich countries for enhanced oil recovery. If the Paris Agreement is to be met, then this progress must be replicated widely, including hydrocarbon-limited countries. In this study, we present a novel source-to-sink assessment methodology based on a hubs and clusters approach to identify favourable regions for CCS deployment and attract renewed public and political interest in viable deployment pathways. Here, we apply this methodology to Spain, where fifteen emission hubs from both the power and the hard-to-abate industrial sectors are identified as potential CO2 sources. A priority storage structure and two reserves for each hub are selected based on screening and ranking processes using a multi-criteria decision-making method. The priority source-to-sink clusters are identified indicating four potential development regions, with the North-Western and North-Eastern Spain recognised as priority regions due to resilience provided by different types of CO2 sources and geological structures. Up to 68.7 Mt CO2 per year, comprising around 21% of Spanish emissions can be connected to clusters linked to feasible storage. CCS, especially in the hard-to-abate sector, and in combination with other low-carbon energies (e.g., blue hydrogen and bioenergy), remains a significant and unavoidable contributor to the Paris Agreement’s mid-century net-zero target. This study shows that the hubs and clusters approach can facilitate CCS deployment in Spain and other hydrocarbon-limited countries., Funding was provided by the Grup Consolidat de Recerca “Geologia Sedimentària” (2017SGR-824) and the DGICYT Spanish Project PGC2018-093903-B-C22. XS acknowledges funding by the China Scholarship Council for a PhD scholarship (201806450043). JA is funded by MICINN (Juan de la Cierva fellowship - IJC2018-036074-I). EGR acknowledges funding provided by MICINN (“Ramón y Cajal” fellowship RYC2018-026335-I). VV acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809). IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S). NH is funded by the Engineering and Physical Sciences Research Council (EPSRC) funded research project “HyStorPor” (EP/S027815/1). SH and AC are funded by EPSRC EP/P026214/1 UKCCSRC 2017, and EU project 837754 - STRATEGY CCUS. DVM is funded by the Spanish Ministry of Science, Innovation and Universities (“Beatriz Galindo Senior” fellowship BEAGAL18/00259). GJ is funded by the University of Strathclyde Faculty of Engineering., Peer reviewed

It is widely accepted that massive deployment of Carbon Capture and Storage (CCS) in geologic
media at the gigatonne scale should be part of the mitigating pathways toward net-zero CO2 emissions. For a
successful geologic CO2 storage, the caprock sealing capacity and the associated governing processes have to
be assessed in detail. In this contribution, we aim at improving our understanding of hydromechanical processes
induced by dynamics of CO2 leakage through intact shaly caprocks. To this end, we perform laboratory
experiments on supercritical CO2 injection into a caprock sample under representative subsurface conditions.
We numerically simulate the process to provide a mechanistic interpretation of experimental observations.
Overall, we find that CO2 intrusion into the pore network increases pore pressure and triggers hydromechanical
coupling effects, mainly causing the specimen to expand after an initial transient compaction. The pressureinduced
rock expansion slightly enhances the porosity and permeability, promoting CO2 flow close to the
upstream. However, the high entry pressure and ultra-low effective permeability of the non-wetting phase limit
the bulk volumetric penetration of CO2 deep into the caprock. Therefore, advective flow of CO2 is restricted to
the lowermost portion of intact caprock, whereas diffusion extends along the whole caprock sample., I.R.K. and V.V. acknowledge funding from the
European Research Council (ERC) under the European
Union’s Horizon 2020 Research and Innovation
Program through the Starting Grant GEoREST
(www.georest.eu) (Grant agreement No. 801809).
IDAEA-CSIC is a Centre of Excellence Severo Ochoa
(Spanish Ministry of Science and Innovation, Project
CEX2018-000794-S). R.M. is thankful for the support
from US DOE through CarbonSAFE Macon County
Project DE-FE0029381., Peer reviewed

Geologic carbon storage is needed to meet the climate goal of limiting global warming to 1.5 ºC. Injecting in deep sedimentary formations brings CO2 to a supercritical state, yet less dense than the resident brine making it buoyant. Therefore, the assessment of the sealing capacity of the caprock lying above the storage reservoir is of paramount importance for the widespread deployment of geologic carbon storage. We perform laboratory-scale supercritical CO2 injection into a representative caprock sample and employ numerical simulations to provide an in-depth understanding of CO2 leakage mechanisms. We explore the effect of relative permeability curves on the potential CO2 leakage through the caprock. We show that capillary breakthrough is unlikely to take place across a non-fractured caprock with low intrinsic permeability and high entry pressure. Rather, CO2 leakage is dominated by the intrinsically slow molecular
diffusion, favoring safe storage of CO2 over geological time scales., I.R.K. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809). IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S). R.M. is thankful for the support from US DOE through CarbonSAFE Macon County Project DE-FE0029381., Peer reviewed

Geologic carbon storage in deep saline aquifers has emerged as a promising technique to mitigate climate change. CO2 is buoyant at the storage conditions and tends to float over the resident brine jeopardizing long-term containment goals. Therefore, the caprock sealing capacity is of great importance and requires detailed assessment. We perform supercritical CO2 injection experiments on shaly caprock samples (intact caprock and fault zone) under representative subsurface conditions. We numerically simulate the experiments, satisfactorily reproducing the observed evolution trends. Simulation results highlight the dynamics of CO2 flow through the specimens with implications to CO2 leakage risk assessment in field practices. The large injection-induced overpressure drives CO2 in free phase into the caprock specimens. However, the relative permeability increase following the drainage path is insufficient to provoke an effective advancement of the free-phase CO2. As a result, the bulk CO2 front becomes almost immobile. This implies that the caprock sealing capacity is unlikely to be compromised by a rapid capillary breakthrough and the injected CO2 does not penetrate deep into the caprock. In the long term, the intrinsically slow molecular diffusion appears to dominate the migration of CO2 dissolved into brine. Nonetheless, the inherently tortuous nature of shaly caprock further holds back the diffusive flow, favoring safe underground storage of CO2 over geological time scales., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. The research presented in this article was funded by the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809). This work was partly supported by the Spanish Ministry of Science and Innovation through the grant CEX2018-000794-S, funded by MCIN/AEI/10.13039/501100011033. Additional support was provided by the grant IJC2020-043809-I funded by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. This study also received the support from US DOE through CarbonSAFE Macon County Project DE-FE0029381. Open access funding provided by the Spanish National Research Council (CSIC)., Peer reviewed

With the urgent necessity of geo-energy resources to achieve carbon neutrality, fluid injection and production in the fractured
media will significantly increase. Applications such as enhanced geothermal systems, geologic carbon storage, and
subsurface energy storage involve pressure, temperature, and stress changes that affect fracture stability and may induce
microseismicity. To eventually have the ability to control induced seismicity, it is first necessary to understand its triggering
mechanisms. To this end, we perform coupled thermo-hydro-mechanical (THM) simulations of cold water injection and
production into a rock containing two fracture sets perpendicular between them. The permeability of fractures being four
orders of magnitude higher than the one of the rock matrix leads to preferential pressure and cooling advancement, which
induce stress changes that affect fracture stability. We find that the fracture set that is oriented favorably to undergo shear slip
in the considered stress regime becomes critically stressed, inducing microseismicity. In contrast, the fracture set that is not
favorably oriented for shear remains stable. These results contrast with those obtained for an equivalent porous media that
does not explicitly include fractures in the model, which fails to reproduce the direction-dependent stability of fractures
present in the subsurface. We contend that fractures should be directly embedded in the numerical models when
inhomogeneities are of the spatial scale of the reservoir to enable reproducing the THM coupled processes that may lead to
induced microseismicity., V.V. acknowledges funding from the European Research Council (ERC) under the
European Union’s Horizon 2020 Research and Innovation Program through the
Starting Grant GEoREST (www.georest.eu (http://www.georest.eu)) under Grant
agreement No. 801809. IDAEA-CSIC is a Centre of Excellence Severo Ochoa
(Spanish Ministry of Science and Innovation, Grant CEX2018-000794-S, funded by
MCIN/AEI/ 10.13039/501100011033). R.M. is thankful for the support from US
DOE through CarbonSAFE Macon County Project DE-FE0029381. F.P. acknowledges
funding from the European Union’s Horizon 2020 Research and Innovation Program
through the Marie Skłodowska-Curie Individual Fellowship ARMISTICE under Grant
agreement No. 882733., Peer reviewed

A recent publication by Cesca et al.1 reanalyzes and expands seismic data to identify hypocenters of observed seismicity induced by the Castor Underground Gas Storage (UGS) operations. Their results confirm those of previous studies2,3 that earthquakes occurred below the storage formation on a fault dipping opposite from the Amposta fault, which bounds the reservoir. However, two important sets of disagreements require revising the conclusions by Cesca et al.1: the depth of hypocenters and the processes leading to seismicity. Inaccurate estimates of hypocenters location and partial consideration of the physical mechanisms that induce seismicity may imply endangering future deep underground projects., V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu) under grant agreement No. 801809. A.V. acknowledges funding from Spanish Ministry of Science and Innovation grant CGL2017-88864-R. IDAEA-CSIC and ICM-CSIC are Centres of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation Grants CEX2018-000794-S and CEX2019-000928-S, respectively, funded by MCIN/AEI/ 10.13039/501100011033), Peer reviewed

Abstract: Guaranteeing the sealing capacity of caprocks becomes paramount as CO2 storage scales up to the gigaton scale. A significant number of laboratory experiments have been performed with samples of intact rock, showing that low-permeability and high-entry pressure caprocks have excellent sealing capacities to contain CO2 deep underground. However, discontinuities, such as bedding planes, fractures and faults, affect the rock properties at the field scale, being at the same time challenging to monitor in industrial-scale applications. To bridge these two spatial scales, Underground Research Laboratories (URLs) provide a perfect setting to investigate the field-scale sealing capacity of caprocks under a well-monitored environment. In particular, the CO2 Long-term Periodic Injection Experiment (CO2LPIE) at the Mont Terri rock laboratory, Switzerland, aims at quantifying the advance of CO2 in Opalinus Clay, an anisotropic clay-rich rock with bedding planes dipping 45° at the experiment location. To assist in the design of CO2LPIE and have an initial estimate of the system response, we perform plane-strain coupled Hydro-Mechanical simulations using a linear transversely isotropic poroelastic model of periodic CO2 injection for 20 years. Simulation results show that pore pressure changes and the resulting stress variations are controlled by the anisotropic behavior of the material, producing a preferential advance along the bedding planes. CO2 cannot penetrate into Opalinus Clay due to the strong capillary effects in the nanoscale pores, but advances dissolved into the resident brine. We find that the pore pressure oscillations imposed at the injection well are attenuated within tens of cm, requiring a close location of the monitoring boreholes with respect to the injection interval to observe the periodic signal. Article highlights: Underground rock laboratory experiments permit examining the caprock sealing capacity at a representative scale for CO2 storage;We perform coupled transverse isotropic hydro-mechanical simulations to gain insight on the response of shaly rock to CO2 periodic injection;Simulation results assist in the design of the injection amplitude and period and monitoring of the long-term periodic CO2 injection experiment., D.S., I.R.K. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant agreement No. 801809. I.R.K. also acknowledges support by the PCI2021-122077-2B project (www.easygeocarbon.com) funded by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Grant CEX2018-000794-S, funded by MCIN/AEI/10.13039/501100011033 ). The authors would like to thank swisstopo and the Mont Terri Consortium for their comprehensive information and very valuable discussions. R.Y.M. acknowledges the support from US DOE through Carbon SAFE Illinois Corridor Project DE-FE0031892., Peer reviewed

The database and its accompanying files are as follows:
GEoREST_database_Readme (.txt): provides an overview of the database goals and content, sharing/accessing information and methodologies used to develop the database.
GEoREST_induced_seismicity_database_v20.11.2022 (.xlsx): database in a single Microsoft Excel spreadsheet.
GEoREST_induced_seismicity_database_v20.11.2022 (.csv): database in ‎.csv format, considered as a standard machine-readable format for direct implementation of data in model developments.
GEoREST_database_bibliography_v20.11.2022 (.docx): provides the full list of references used to collect data included in the database.
GEoREST_database_dictionary_v20.11.2022 (.docx): presents unified, self-explanatory acronyms together with concise definitions for all variables included in the database., We present a comprehensive, publicly accessible database of injection-induced seismicity. The database is sourced from a comprehensive review of more than 500 published documents and contains information for 158 cases of induced earthquakes from around the world. The collected earthquakes are associated with a variety of geoenergy applications, which can be broadly categorized into geologic gas storage, geothermal energy development, shale gas fracturing, research projects and wastewater disposal. The compilation comprises more than 70 variables, including general project information, host rock properties, ‎in situ site characteristics, fault attributes, operational parameters, and recorded seismicity data (both overall seismic activities and the largest event sequence). The developed database opens up opportunities for improved understanding of the causative mechanisms of injection-induced seismicity and advancing on seismic hazard forecasting and mitigation., This research is funded by
(1) the European Research Council (ERC) under ‎the ‎‎European Union’s Horizon ‎‎2020
Research and Innovation Program through the ‎Starting Grant ‎‎GEoREST (www.georest.eu) under Grant ‎agreement No. 801809,
(2) MCIN/AEI/‎‎10.13039/501100011033 and the ‎European ‎Union ‎NextGenerationEU/PRTR
through the international collaboration project EASYGEOCARBON ‎‎‎‎(www.easygeocarbon.com)
under Grant ‎agreement No. PCI2021-122077-2B,
(3) the European Union’s Horizon 2020 Research and Innovation ‎Programme
through the Marie Sklodowska-Curie Action ARMISTICE (www.armistice-energy.eu) under grant â
€Žagreement No. 882733.
(4) the Secretariat for Universities and ‎Research of the Ministry of Business and Knowledge of the
Government of Catalonia (AGAUR) and the European ‎Social Fund (FI-2019),
(5) MCIN/AEI/ ‎‎10.13039/501100011033‎ through the Excellence Servero Ochoa (IDAEA-CSIC) under Grant agreement No. ‎CEX2018-000794-S, Peer reviewed

The effectiveness of Carbon Capture and Storage (CCS) as an imperative decarbonization technology relies on the sealing capacity of a fine-grained caprock to permanently store CO2 deep underground. Uncertainties in assessing the caprock sealing capacity increase with the spatial and temporal scales and may delay CCS deployment at the gigatonne scale. We have developed a computationally efficient transport model to capture the dynamics of basin-wide upward CO2 migration in a multi-layered setting over geological time scales. We find that massive capillary breakthrough and viscous flow of CO2, even through pervasively fractured caprocks, are unlikely to occur and compromise the storage security. Potential leakage from the injection reservoir is hampered by repetitive layering of overlying caprocks. This finding agrees with geologic intuition and should be understandable by the public, contributing to the development of climate policies around this technology with increased confidence that CO2 will be indefinitely contained in the subsurface., I.R.K. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant agreement No. 801809. I.R.K. also acknowledges support by the PCI2021-122077-2B project (www.easygeocarbon.com) funded by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Grant CEX2018-000794-S funded by MCIN/AEI/10.13039/501100011033). R.Y.M. acknowledges the support from US DOE through Carbon SAFE Illinois Corridor Project DE-FE0031892. Additional funding for completing this manuscript was provided to C.M.O. and J.R. by the U.S. Department of Energy under contract No. DE-AC0205CH11231 to the Lawrence Berkeley National Laboratory., Peer reviewed

Induced seismicity is a limiting factor for the development of Enhanced Geothermal Systems (EGS). Its causal mechanisms are not fully understood, especially those of post-injection seismicity. To better understand the mechanisms that induced seismicity in the controversial case of the Basel EGS (Switzerland), we perform coupled hydro-mechanical simulation of the plastic response of a discrete pre-existing fault network built on the basis of the monitored seismicity. Simulation results show that the faults located in the vicinity of the injection well fail during injection mainly triggered by pore pressure buildup. Poroelastic stressing, which may be stabilizing or destabilizing depending on the fault orientation, reaches further than pressure diffusion, having a greater effect on distant faults. After injection stops, poroelastic stress relaxation leads to the immediate rupture of previously stabilized faults. Shear-slip stress transfer, which also contributes to post-injection reactivation of distant faults, is enhanced in faults with slip-induced friction weakening., A.B. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant agreement No. 801809. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Grant CEX2018-000794-S funded by MCIN/AEI/ https://doi.org/10.13039/501100011033). This research has been carried out within the framework of the activities of the Spanish Government through the “Maria de Maeztu Centre of Excellence” accreditation to IMEDEA (CSIC-UIB) (CEX2021-001198)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2018-000794-S), With funding from the Spanish government through the ‘María de Maeztu Unit of Excelence’ accreditation (CEX2021-001198), Peer reviewed

Trabajo presentado en la 3rd International Conference on Coupled Processes in Fractured Geological Media: "Observation, Modeling, and Application" (Coufrac 2022), celebrada en Berkeley (USA) entre el 14 y el 16 de noviembre de 2022., Pressure buildup is the standard, but often insufficient, explanation for induced seismicity, , especially when it comes to delayed effects. Coupled processes may play relevant roles, so that they must be accounted for to find the mechanisms triggering induced seismicity, especially when it comes to delayed effects. We illustrate the importance of coupled processes in induced seismicity through the case of the Underground Gas Storage (UGS) project of Castor, Spain, where, cushion gas injection induced hundreds of events, with maximum magnitudes of 4.1, leading to the cancellation of the project. Gas injection lasted for 15 days, and the largest earthquakes occurred 17 days after the stop of injection. Injection overpressures had dissipated by the time of the largest events. The gas was injected at 1.7 km depth, while the induced seismicity occurred at depths ranging from 4 to 10 km. These characteristics of the induced seismicity at Castor pose a challenge on explaining its causes. Coupled processes provide a plausible explanation when combining poromechanical stresses, buoyancy, and shear-slip stress transfer. If coupled processes had been considered in the assessment of the induced seismicity at Castor, the induced earthquakes at Castor could have been anticipated and managed., V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu) under grant agreement No. 801809. A.V. acknowledges funding from Spanish Ministry of Science and Innovation grant CGL2017-88864-R. IDAEA-CSIC and ICM-CSIC are Centres of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation Grants CEX2018-000794-S and CEX2019-000928-S, respectively, funded by MCIN/AEI/ 10.13039/501100011033)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2018-000794-S) y (CEX2019-000928-S), Peer reviewed

[Date of data collection] Feb. 2020 for field data and Jan. 2022- Jan. 2023 for numerical models., This dataset includes the input files of the numerical models used in the manuscript for simulating the hydraulic stimulation at the Bedretto lab. Each folder is named after the corresponding model in the manuscript, i.e., EP (Elastic Prescribed), EE (Elastic Embedded), and VE (Viscoplastic Embedded). In each folder, there is a file with the name of the folder ended as “_gen.dat” which contains the input data of the model, including material properties, initial and boundary conditions and the time intervals. There is also a file ended as “_gri.dat” that includes the information on the mesh. The file “root.dat” includes the name of the model. The file ended as “_bcf.dat” contains injection rate input., European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), under grant agreement No. 801809.
Swiss Federal Office of Energy within the framework of the ZoDrEx GEOTHERMICA project under contract SI/501720-01. European Union’s Horizon 2020 Research and Innovation Program through the Marie Sklowdowska-Curie Individual Fellowship ARMISTICE, under Grant Agreement No. 882733.
The “ZoDrEx” project, which has been subsidized through the ERANET Cofund GEOTHERMICA (Project No. 731117), from the European Commission and the Spanish Ministry of Economy, Industry and Competitiveness (MINECO). IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., 1-EP_bcf.dat 1-EP_gen.dat 1-EP_gri.dat root.dat 2-EE_bcf.dat 2-EE_gen.dat 2-EE_gri.dat root.dat 3-VE_bcf.dat 3-VE_gen.dat 3-VE_gri.dat root.dat 3-VE-Extended_bcf.dat 3-VE-Extended_gen.dat 3-VE-Extended_gri.dat root.dat, Peer reviewed

Induced seismicity compromises the widespread deployment of geoenergy applications that contribute to mitigate climate change. In particular, the development of Enhanced Geothermal Systems (EGS) has been hindered by the risk of induced seismicity, mostly caused by hydraulic stimulation aimed at enhancing the permeability of deep hot crystalline rocks. Injection‐induced seismicity has been traditionally attributed to fluid pressure buildup, which destabilizes fractures and faults. However, the largest seismic events commonly occur after the stop of injection, when pore pressure drops and both the magnitude and frequency of induced seismicity is expected to decrease. This counterintuitive phenomenon is not well understood. Yet, understanding the triggering mechanisms is the key to reliably forecast and manage induced seismicity. Here, we investigate the triggering mechanisms of co‐ and post‐injection seismicity using coupled hydromechanical models, considering both a homogeneous and a fault‐crossed domain, based on the case of Basel EGS (Switzerland). We find that the combination of pressure diffusion, poroelastic stressing, and static stress transfer explains the occurrence of induced seismicity, especially after the stop of injection, significantly better than the pore pressure alone. Considering a fault zone, which is more permeable and deformable than the surrounding rock, amplifies pressure diffusion along the fault and causes anisotropic variations of the stress field that lead to an increase in the seismicity rate that is orders of magnitude larger than for the homogeneous domain. These results point out that identifying the main geological structures through subsurface characterization is key to improve physics‐based induced seismicity forecasting., A.B. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant agreement No. 801809. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Grant CEX2018-000794-S funded by MCIN/AEI/ 10.13039/501100011033). IMEDEA is an accredited"Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033) S.D.S. acknowledges the support of the European Union “Next Generation EU”/PRTR and the Spanish Ministry of Science and Innovation through the ‘Ramón y Cajal’ fellowship (reference RYC2021-032780-I)., Peer reviewed

Fluid injection into geological formations for energy resource development frequently induces (micro)seismicity. Moderate- to large-magnitude induced earthquakes may cause injuries and/or economic loss, with the consequence of jeopardizing the operation and future development of these geo-energy projects. To achieve an improved understanding of the mechanisms of induced seismicity, develop forecasting tools and manage the associated risks, it is necessary to carefully examine seismic data from reported cases of induced seismicity and the parameters controlling them. However, these data are challenging to gather together and are time-consuming to collate as they come from different disciplines and sources. Here, we present a publicly available, multi-physical database of injection-induced seismicity (Kivi et al., 2022a; 10.20350/digitalCSIC/14813), sourced from an extensive review of published documents. Currently, it contains 158 datasets of induced seismicity caused by various subsurface energy-related applications worldwide. Each dataset covers a wide range of variables, delineating general site information, host rock properties, in situ geologic and tectonic conditions, fault characteristics, conducted field operations, and recorded seismic activities. We publish the database in flat-file formats (i.e., .xls and .csv tables) to facilitate its dissemination and utilization by geoscientists while keeping it directly readable by computer codes for convenient data manipulation. The multi-disciplinary content of this database adds unique value to databases focusing only on seismicity data. In particular, the collected data aim at facilitating the understanding of the spatiotemporal occurrence of induced earthquakes, the diagnosis of potential triggering mechanisms, and the development of scaling relations of maximum possible earthquake magnitudes and operational parameters. The database will boost research in seismic hazard forecasting and mitigation, paving the way for increasing contributions of geo-energy resources to meeting net-zero carbon emissions., The authors acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the starting grant GEoREST (http://www.georest.eu, last access: 23 July 2023) under grant agreement no. 801809. Iman R. Kivi and Victor Vilarrasa also acknowledge support by the PCI2021-122077-2B project (http://www.easygeocarbon.com, last access: 23 July 2023), funded by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. Haiqing Wu acknowledges the financial support received from the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia (AGAUR) and the European Social Fund (FI-2019). Haiqing Wu also acknowledges the Becas Santander Research Scholarship from the Technical University of Catalonia (UPC) and Santander. Francesco Parisio and Victor Vilarrasa acknowledge funding from the European Union's Horizon 2020 Research and Innovation Programme through the Marie Skłodowska-Curie Action ARMISTICE under grant agreement no. 882733. IDAEA-CSIC is a Centre of Excellence Servero Ochoa (Spanish Ministry of Science and Innovation, grant no. CEX2018-000794-S, funded by MCIN/AEI/10.13039/501100011033). IMEDEA is an accredited “Maria de Maeztu Excellence Unit” (grant no. CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033)., Peer reviewed

This dataset includes the input files of the numerical models used in the manuscript for simulating the hydraulic stimulation in Enhanced Geothermal System with a single fracture setup. Each folder is named after the corresponding injection protocol in the manuscript, i.e., Constant, Step, and Cyclic. In each of these folders, there are two subfolders namely- Without Bleedoff and With Bleedoff. In the subfolders, the file ending with “_gen.dat” contains the input data of the model, including material properties, initial and boundary conditions and the time intervals. There is also a file ending with “_gri.dat” that includes the information on the mesh. The file “root.dat” includes the name of the model., European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), under grant agreement No. 801809.
European Union’s Horizon 2020 Research and Innovation Program through the Marie Sklowdowska-Curie Individual Fellowship ARMISTICE, under Grant Agreement No. 882733.
IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (Grant CEX2021-001198)., README.txt (this file) Constant_0p3_gen.dat Constant_0p3_gri.dat root.dat Constant_0p3_bleedoff_gen.dat Constant_0p3_bleedoff_gri.dat root.dat Step_0p3_gen.dat Step_0p3_gri.dat root.dat Step_0p3_bleedoff_gen.dat Step_0p3_bleedoff_gri.dat root.dat Cyclic_0p3_gen.dat Cyclic_0p3_gri.dat root.dat Cyclic_0p3_bleedoff_gen.dat Cyclic_0p3_bleedoff_gri.dat root.dat, Peer reviewed

This dataset encompasses the input files associated with diverse analytical and numerical models investigating cyclic pressure diffusion within uniform poroelastic materials. The dataset is organized into two primary folders. The "Analytical Solutions" folder comprises three Python libraries containing the material properties and functions for calculating pressure amplitude at various distances.
The "Numerical Solutions" folder contains simulations for both Hydraulic ("01_") and Hydro-Mechanical ("HM_") problems. The simulations are conducted for representative values corresponding to Berea sandstone ("BS_"), Opalinus Clay ("OPA_"), and Westerly granite ("WG_"), considering both monodimensional ("1D") and axisymmetric ("Ax") cases. Within each subfolder, files with the suffix "_gen.dat"
provide input data for the model, encompassing material properties, initial and boundary conditions, and time intervals. Correspondingly, files concluding with "_gri.dat" contain information of the mesh employed. The "_bfc.dat" file documents the periodic injection pressure applied for each simulation, while the "root.dat" file specifies the model's nomenclature. To execute a model, launching the executable "Cb_v9_1_3par4.exe" within each ".gid" folder is sufficient., European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), under grant agreement No. 801809.
IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., File List: README.txt (this file) \Analytical Solutions\CyclicDiffusion.py \Analytical Solutions\CyclicDiffusion_Adimensional.py \Analytical Solutions\Materials.py \Numerical Solutions\01_BS_1D_g0_1yr.gid \Numerical Solutions\01_BS_Ax_g0_1yr.gid \Numerical Solutions\01_OPA_1D_g0_1w.gid \Numerical Solutions\01_OPA_Ax_g0_1w.gid \Numerical Solutions\01_WG_1D.gid \Numerical Solutions\01_WG_Ax.gid \Numerical Solutions\HM_BS_1D_g0_1yr.gid \Numerical Solutions\HM_BS_Ax_g0_1yr.gid \Numerical Solutions\HM_OPA_1D_g0_1w.gid \Numerical Solutions\HM_OPA_Ax_g0_1w.gid \Numerical Solutions\HM_WG_1D.gid \Numerical Solutions\HM_WG_Ax.gid \Numerical Solutions\Cb_v9_1_3par4.exe, Peer reviewed

Any usage of field data should aquire permission from Geo-Energie Suisse., This dataset includes the input files of the numerical models used in the manuscript for simulating the hydraulic stimulation in the conceptual models as well as the Bedretto model with the executable file of the numerical code (CODE_BRIGHT). Each folder is named after the corresponding model in the manuscript described in the sections 3.1.1 and 3.2.1.
In each folder, there is a file with the name of the folder ended as “_gen.dat” which contains the input data of the model, including material properties, initial and boundary conditions and the time intervals. There is also a file ended as “_gri.dat” that includes the information on the mesh. The file “root.dat” includes the name of the model. The file ended as “_bcf.dat” contains injection rate input for Bedretto model. To run the simulation, copy and paste Code_Bright executable file, i.e., “Cb_2021.exe”, in a folder that contains the input files and execute it., European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), under grant agreement No. 801809.
Swiss Federal Office of Energy within the framework of the ZoDrEx GEOTHERMICA project under contract SI/501720-01.
European Union’s Horizon 2020 Research and Innovation Program through the Marie Sklowdowska-Curie Individual Fellowship ARMISTICE, under Grant Agreement No. 882733.
The “ZoDrEx” project, which has been subsidized through the ERANET Cofund GEOTHERMICA (Project No. 731117), from the European Commission and the Spanish Ministry of Economy, Industry and Competitiveness (MINECO).
EURAD, the European Joint Programme on Radioactive Waste Management through the project DONUT (Grant No 847593), Peer reviewed

This dataset corresponds to the model made from the EGS project of Basel (2006, Switzerland). The model is solving coupled hydromechanical problem for 2D fault network on a surface of 1 km2, located at 4630-meters depth coinciding with the injection depth in the crystalline basement at Basel. A set of faults are embedded in a rock matrix, with the fault network derived from the induced seismicity that was monitored in the range of 3750 and 4750 meters deep. The maximum principal stress S_Hmax is aligned with y-axis (S_Hmax=160 MPa, S_hmin=84 MPa, S_v=115 MPa).
The hydrostatic pressure is set at 45 MPa following a hydrostatic profile and the temperature at the depth of the reservoir is set at 190°C. Stimulation parameters are inputs as wellhead pressure based on the injection strategy from Häring et al. (2008), injection fluid is water.
- “ .gid” is the Code_Bright file with the model of Basel. The file “_gen.dat” contains the input data of the model (including material properties, initial and boundary conditions and the time intervals). The file “_gri.dat” includes the information on the mesh. The “root.dat” includes the name of the model. To run simulations, execute the Code_Bright executable “Cb_2020_21.exe” in a folder that contains the three input files and the executable, where X and Y denote the used version of the executable.
• V13_C_NW_longbleed.gid corresponds to the model in which the bleed-off of the well is imposed.
• V13_C_NW_shutin.gid corresponds to the model in which the injection well is shut-in., Horizon 2020 Research and Innovation Program through the ‎Starting Grant ‎GEoREST under Grant agreement No. 801809, - V13_c_NW_longbleed.gid - V13_c_NW_shutin.gid - Readme.docx, Peer reviewed

Quick estimates of fluid-induced subsurface deformation are helpful to assess the land uplift/subsidence and to reveal precursors of induced seismicity. Here, we adopt the inclusion theory and Green's function to develop a closed-form solution in a half space for the poroelastic response of a reservoir compartmentalized by an intersecting fault that can be offset and either permeable or impermeable. Simulated results reveal that (1) fault permeability mainly impacts the spatial distribution of displacement while its effect on displacement magnitude is small; (2) ground displacement slightly increases with fault dip while slightly decreases with increasing fault offset; in contrast, reservoir geometry shows a stronger effect than fault geometry: the ground displacement is proportional to the vertical and lateral depth ratios, defined as the ratios of reservoir thickness (h) and width (w) to reservoir depth (D), respectively; (3) the maximum vertical displacement is the double of the horizontal one regardless of fault permeability, fault and reservoir geometries, and mechanical parameters. Comparing the solution in a half space with that in a full space shows that neglecting the free surface underestimates the poroelastic displacement in the overburden. The validity of full-space solutions can be assessed with the product of the lateral and vertical depth ratios, i.e., wh/D2. The full-space solutions become valid when wh/D2 decreases to an intrinsic threshold. This threshold may range from 0.01 to 0.02 for displacement, and its specific value depends on the field background and demands of projects, but can be estimated based on our solution. It is larger for stress than for displacement, and wh/D2 ≤ 0.1 is recommended as a general condition for neglecting the free-surface effects on induced stress. The analytical solution represents a useful tool for estimating ground deformation and for gaining insights of reservoir and fault geometries by analyzing surface deformation patterns., H.W. would like to acknowledge the financial support received from the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia (AGAUR) and the European Social Fund (FI-2019). H.W. also acknowledges the Becas Santander Research Scholarship from the Technical University of Catalonia (UPC) and the Santander. J.R. acknowledges funding by the Assistant Secretary for Fossil Energy, National Energy Technology Laboratory, National Risk Assessment Partnership of the U.S. Department of Energy to the Lawrence Berkeley National Laboratory under contract no. DEAC02-05CH11231. V.V. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant agreement No. 801809. IMEDEA is an accredited “Maria de Maeztu Excellence Unit” (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., Peer reviewed

© 2024 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)., Injection-induced seismicity has become one of the most critical challenges for the widespread deployment of Enhanced Geothermal Systems (EGS). In particular, some EGS development projects have led to large, damaging earthquakes that unexpectedly occurred far off the stimulated reservoir region and, in particular, after stopping fluid injection. Yet, the causative mechanisms of these seismicity patterns remain highly elusive. Here, we identify a combination of mechanisms that could explain delayed seismicity in EGS sites by conducting fully-coupled hydromechanical simulations of the hydraulic stimulation of a naturally-fractured granitic reservoir. The model comprises a sparse network of long, variably-oriented fractures interacting with a nearby, critically-oriented fault. The results show that the presence of fractures introduces notable nonlinearities in the flow field and rock deformation and significantly expands the rock volume affected by fluid injection. First, the stimulated fracture network provides highly-permeable conduits for communicating elevated pore pressure over long distances. Second, the anisotropic expansion of fractures generates shear stress that is transmitted almost instantaneously across the reservoir. The pore pressure and stress perturbations can not only cause slip along fractures, inducing (micro)seismicity during injection, but also affect the stability of nearby faults, which may not necessarily be pressurized during injection. The transferred poroelastic stresses can increase or decrease the slip tendency along different fault segments. However, the fault may reactivate only after several months following injection when a progressive pore pressure diffusion modulated by the transient fault permeability evolution brings a critically-stressed fault segment to failure conditions. We also find that the spatiotemporal evolution of seismicity depends largely on the nearby fault orientation, hydromechanical properties, and hydraulic connection with the fracture network, as well as the initial state of stress. We conclude that accurate subsurface characterization and continuous monitoring during and after injection should allow for managing the risks posed by injection-induced seismicity and safely unlocking the immense potential for clean and sustainable geothermal energy., I.R.K. and V.V. acknowledge support by the PCI2021-122077-2B project (http://www.easygeocarbon.com) funded by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. I.R.K. also acknowledges funding from the Engineering and Physical Sciences Research Council through the UKRI Postdoc Guarantee Award THMC4CCS [Grant number EP/X026019/1]. V.V. also acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (http://www.georest.eu) under Grant agreement No. 801809. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Grant CEX2018-000794-S funded by MCIN/AEI/10.13039/501100011033). IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033). K.I.K. acknowledges support by the Innovative Technology Development Program for High-level waste management of the National Research Foundation of Korea (NRF) funded by the Korea government (Ministry of Science and ICT, MSIT) (Grant No.2021M2E3A2041312). K.-B.M. and H.Y. were supported by a grant from the Human Resources Development program (No. 20204010600250) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), funded by the Ministry of Trade, Industry, and Energy of the Korean Government. K.-B.M. and H.Y. were also supported by the Innovative Technology Development Program for High-level waste management of the National Research Foundation of Korea (NRF) funded by the Korea government (Ministry of Science and ICT, MSIT) (Grant No. 2021M2E3A2044264)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2018-000794-S)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198-S)., Peer reviewed

Ph.D. thesis Civil Engineering Program, UPC. Hydrogeology Group (GHS), Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya (UPC), Instituto Mediterráneo de Estudios Avanzados (IMEDEA, CSIC)., This thesis was funded from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant agreement No. 801809., Peer reviewed

This dataset encompasses the input files associated with diverse numerical models investigating the hydro-mechanical behavior of a fractured specimen under different mean effective stresses. The folder contains simulations for Hydro-Mechanical ("HM_") problems. The simulations are conducted for different mean effective stresses ("P03"; "P05"; "P10"; "P15"; and "P20"). Within each subfolder, files with the suffix "_gen.dat" provide input data for the model, encompassing material properties, initial and boundary conditions, and time intervals. Correspondingly, files concluding with "_gri.dat"
contain information on the mesh employed. To execute a model, launching the executable "Cb_v9_1_3par4.exe" within each ".gid" folder is sufficient., European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), under grant agreement No. 801809.
IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., README.txt (this file) \HM_P03.gid \HM_P05.gid \HM_P10.gid \HM_P15.gid \HM_P20.gid \HM_P20_higherKn.gid, Peer reviewed

© 2024 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)., Hydraulic stimulation of Enhanced Geothermal Systems (EGS) aims at boosting permeability to facilitate fluid circulation, while keeping a low induced seismicity. However, some stimulations have led to poor permeability enhancement or too high induced earthquakes, which suggests that further understanding is needed on poromechanical processes during stimulation. Here, we model a highly-monitored test performed at the Bedretto Underground Laboratory to investigate the impact of fluid injection on permeability enhancement and induced microseismicity. We examine three models: (1) a homogeneous fracture whose transmissivity is manually calibrated to reproduce the observed pressure evolution at the injection borehole (this model fails to capture the spatial distribution of pressure and the corresponding poromechanical processes); (2) an elastic fracture approach, where transmissivity changes locally as a function of fracture aperture following the cubic law (this model overestimates pressure after the onset of fracture slip); and (3) a viscoplastic fracture approach with strain weakening and dilatancy that yields an additional permeability enhancement after shear reactivation. The viscoplastic model captures the spatio-temporal coupled response of the fractured rock to hydraulic stimulation before and after shearing both in terms of pressure and microseismicity. Subsequently to the onset of shear failure, microseismic events occur in every injection cycle as the reactivation front advances when plastic strain and, thus, permeability surpass the previously achieved maximum value. This viscoplastic model permits estimating the extent of the stimulated fracture, the permeability enhancement and its impact on the local state of stress and pore pressure at surrounding fractures, representing a useful tool for the design of effective hydraulic stimulation., I.V. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), under grant agreement No. 801809. The work of Geo-Energie Suisse AG was financially supported by the Swiss Federal Office of Energy within the framework of the ZoDrEx GEOTHERMICA project under contract SI/501720-01. F.P. and V.V. acknowledge funding from the European Union’s Horizon 2020 Research and Innovation Program through the Marie Sklowdowska-Curie Individual Fellowship ARMISTICE, under Grant Agreement No. 882733. J.C. and V.V. acknowledges financial support from the “ZoDrEx” project, which has been subsidized through the ERANET Cofund GEOTHERMICA (Project No. 731117), from the European Commission and the Spanish Ministry of Economy, Industry and Competitiveness (MINECO). IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033). IDAEA-CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2018-000794-S)., Peer reviewed

Department of Civil and Environmental Engineering (DECA), Universitat Politècnica de Catalunya (UPC), PhD program in civil engineering.-- Supervised by Dr. Víctor Vilarrasa Riaño and Dr. Iman Rahimzadeh Kivi.--
Tutored by Dr. Sebastià Olivella Pastalle.-- Defendida en la Universitat Politècnica de Catalunya (UPC-BarcelonaTech) el 9 de febrero de 2024 con Excelente Cum Laude., Geological Carbon Storage (GCS) is considered a promising technology to lower atmospheric emissions of CO2. Guaranteeing the sealing capacity of caprocks in this case becomes paramount as CO2 storage scales up to the gigaton scale. Many laboratory experiments have been performed with samples of intact rock, showing that low-permeability and high-entry pressure caprocks have excellent sealing capacities to contain CO2 deep underground. However, discontinuities, such as bedding planes, fractures, and faults, affect the rock properties at the field scale, being at the same time challenging to monitor in industrial-scale applications. The main objective of the thesis is to develop a methodology to characterize potential sites for low-carbon geo-energy applications at multiple scales in space and time, taking into account coupled processes. To achieve this objective, it is necessary to understand the complexity of the problem at multiple scales, starting from large-scale investigations, passing through in-situ underground rock laboratories, to laboratory investigations.
This is why this thesis approaches characterizations that span a wide range of spatiotemporal scales from the order of millimeters and nanoseconds to the order of kilometers and decades.
To achieve this general objective, the first part of the thesis explores four analytical solutions of pore pressure diffusion with periodic sources under relevant model geometries and boundary conditions to enable real-time interpretation of in-situ data. We compare the results with numerical solutions, assuming the same conditions as the analytical cases and incorporating reservoir deformation due to pressure waves. Encompassing three different cases to span a wide array of scenarios, we evaluate the attenuation of the signal at varying distances from the source. Numerical and analytical solutions fit when identical assumptions are upheld. Furthermore, the influence of effective mean stress variations yields errors of less than 3% across all the considered cases. Our findings reveal distinct wave propagation depending on the application. For energy storage in highly porous and permeable rocks, the wave propagation extends over kilometer scales. In the case of liquid injection into tight shale, the wave propagation is confined to tens of centimeters. Meanwhile, for enhanced geothermal systems stimulation in crystalline rock, the wave propagation occurs in the order of tens of meters. While numerical solutions can consider multidimensional hydro-mechanical rock response to periodic signals, analytical solutions provide an immediate initial approximation of the problem, enabling rapid reactions to unexpected events.
Next, we perform plane-strain coupled hydro-mechanical simulations using a linear transversely isotropic poroelastic model of periodic
CO2 injection for 20 years to simulate the planned CO2LPIE experiment at Mont Terri Underground Rock Laboratory, in Switzerland. Simulation results show that pore pressure changes and the resulting stress variations are controlled by the anisotropic behavior of the material, producing a preferential advance along the bedding planes. CO2 cannot penetrate Opalinus Clay due to the strong capillary effects in the nanoscale pores, but advances dissolved into the resident brine. We find that the pore pressure oscillations imposed at the injection well are attenuated within tens of cm, requiring a close location of the monitoring boreholes for the injection interval to observe the periodic signal.
Finally, we develop a 3D numerical model of water injection into the fractured specimen to replicate steady-state flow experiments on a naturally fractured Opalinus Clay specimen. This model explicitly accounts for fracture geometry with stress-dependent aperture changes.
Simulation results reveal that fracture permeability spans up to nine orders of magnitude. This significant change in permeability has profound implications for the fluid flow within the rock specimen. Our numerical model achieves the best fit with the experimental results by incorporating a natural fracture normal stiffness from 18.7 MPa/mm at effective mean stresses below 12 MPa to 187.2 MPa/mm at higher confinements. This outcome highlights the critical importance of defining the hydro-mechanical parameters of fractures under realistic effective stress conditions with far-reaching implications for secure underground storage., This thesis was founded by the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant agreement No. 801809., Peer reviewed

A Mw 5.5 earthquake struck Pohang (South Korea) on November 2017, following a sequence of five hydraulic stimulations of an Enhanced Geothermal System (EGS). The processes that led to this earthquake, which nucleated two months after the end of the last stimulation in borehole PX2, are not well understood yet. We propose a hydromechanical model that integrates available data to understand the potential relationship between the earthquake and the EGS. Data scarcity is translated into model uncertainties, which we address with sensitivity analyses. Results show that the Mw 5.5 earthquake is linked to the high-injection overpressures of up to 90 MPa induced during the stimulations in borehole PX2 and highlight the usefulness of hydromechanical modeling to forecast the seismicity of an EGS and, more specifically, the need to integrate the low permeability fault core that hindered fluid pressure dissipation at Pohang, which explains the long delay of the mainshock., The work of Andrés Alcolea and Peter Meier was supported by the European Union Horizon 2020 research and innovation programme under grant agreement number 691728, and by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 15-0316-1. The opinions expressed and arguments employed herein do not necessarily reflect the official views of the Swiss Government. Víctor Vilarrasa acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu) under grant agreement no. 801809. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, grant CEX2018-000794-S funded by MICIU/AEI/10.13039/501100011033). IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (grant CEX2021-001198, funded by MICIU/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2018-000794-S)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., Peer reviewed

© 2024 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)., To harness the immense potential of geothermal energy for non-intermittent baseload power, low-permeability crystalline hot rocks need to be hydraulically stimulated to create Enhanced Geothermal Systems (EGS) that enable economically profitable fluid flow rates. However, hydraulic stimulation is usually associated with seismic activity that has led to project cancellation in a few occasions. To improve our understanding of the coupled hydro-mechanical (HM) processes behind stimulation during both injection and post-injection stages (after shut-in), we numerically analyze three different stimulation protocols: constant-rate, step-rate, and cyclic injection with and without bleed-off after shut-in (and between cycles for the cyclic protocol). Simulation results show that the injection protocol has a higher influence on the HM response of the fracture than the total volume of injected water, which challenge scaling laws that relate the injection volume with the expected maximum magnitude of the induced earthquakes. The trade-off between maximizing permeability enhancement, while minimizing induced seismicity is not straightforward. In particular, bleeding-off the well after injection restricts induced seismicity, but at the expenses of limiting permeability enhancement. When considering stimulation of a single fault, all protocols yield comparable slip rates and, thus, magnitude of the induced earthquake, with the constant-rate injection being the fastest to induce the largest earthquake. The small differences in the HM response to hydraulic stimulation do not permit identifying a protocol that performs better than the others., European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program, grant agreement no. 801809.

Marie Sklodowska-Curie Action Individual Fellowship, grant agreement no. 882733.

Maria de Maeztu Excellence Unit (CEX2021-001198/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., Peer reviewed

GEoREST Workshop on Induced Seismicity that took place from 11th to 13th of March 2024 in Palma., The threat and occurrence of high-magnitude, uncontrolled induced seismicity has been a persisting issue in several kinds of subsurface systems for decades now. Research on limiting induced seismicity to improve the safety of these systems began ever since the first observed cases in wastewater injection. The number of groups working to solve this problem only increased with every major event, focusing on various aspects of induced seismicity. Our understanding of the underlying processes has improved consistently, but the recent events at Pohang, Castor, Groningen, etc., have showcased that there is more to learn in terms of the physics, and demand better characterization, monitoring and forecasting systems in place., This Workshop aims at fostering debate on the latest advances in process understanding, subsurface characterization and forecasting of induced seismicity. We welcome contributions from the academia and industry alike in topics ranging from, but not limited to numerical modeling, laboratory experiments, field studies, application of AI in induced seismicity, etc. We welcome contributions in the form of both posters and oral presentations that broadly fit into the following sessions: + Session 1: Understanding of the causes of induced seismicity + Session 2: Post-injection seismicity: can we forecast it? + Session 3: Subsurface characterization + Session 4: Forecasting induced seismicity + Session 5: Case Studies of induced seismicity., ERC NUMBER — 801809 — GEoREST., Session 1 Understanding of the causes of induced seismicity: Gillian Foulger: HiQuake – a global database of human-induced earthquakes; Keita Yoshioka: Remote hydraulic fracturing at weak interfaces; Marie Violay: Studying Fluid-Induced Earthquakes in the Lab; Jan Dirk Jansen: The Onset of Depletion-Induced Seismicity in Faulted Reservoirs: Uenishi and Rice revisited; Iman R. Kivi: A multi-physics database of injection-induced seismicity in geo-energy projects; Yury Alkhimenkov: Three-dimensional numerical modeling of induced seismicity using high-performance; Haiqing Wu: Poroelastic effects on the nucleation process of dynamic fault rupture during fluid injection; Sandro Andrés Martínez: Pore pressure-dependent friction laws: effects on seismic rupture propagation; Kim Taeho: Factors Controlling Rate and Magnitudes of Induced Seismicity; Sri Kalyan Tangirala: The role of injection protocol on fracture stimulation in enhanced geotermal systems (EGS).-- Session 2 Post-injection seismicity: can we forecast it?: Jean Schmittbuhl: The 2019-2022 sequence of induced seismicity below the city of Strasbourg, France; Yusuke Mukuhira:Revisiting pore pressure behavior at the shut-in phase and causality of large induced seismicity at Basel, Switzerland; Alexis Sáez: Reactivation of fault slip during and after fluid injections; Auregan Boyet: Physic-based modelling to understand and forecast post-injection induced seismicity applied to the Enhanced Geothermal Systems of Basel, Switzerland; Yinlin Ji: Mitigated post-injection seismicity associated with fluid extraction in Enhanced Geothermal Systems: Evidence from lab- and field-scale experiments; Regina Fakhretdinova: Revisiting the Basel-1 hydraulic stimulation with a coupled hydro-mechanical model.-- Session 3 Subsurface characterization: Leo Eisner: Seismic noise model for optimized induced seismicity monitoring; Silvia De Simone: On the equivalent Biot and Skempton coefficients of fractured rocks and their impact on the HM behavior of geological media; Zuzana Jechumtálová: Optimal seismic monitoring network for CO2 injection; Sarah Weihmann: Faults, fractures and the future: unveiling the subsurface for a sustainable energy transition; Qinghua Lei: Characterisation and modelling of fracture networks in rock with application to tunnelling-induced seismicity; Dario Sciandra: Characterizarion of hydro-mechanical properties of fractures in sale; Liudmyla Shumlianska: Nonlinearity approximation and its use in the study of induced seismicity.-- Session 4 Forecasting induced seismicity: Jesús Carrera: Seismicity induced by geoenergy projects: review of processes and simulation methods; Ioannis Stefanou: Preventing human-induced seismicity to fight climate change; James Verdon: An empirically constrained forecasting strategy for induced earthquake magnitudes using extreme value theory; Serge Shapiro: Seismotectonic continuum and the probability of maximum earthquakes triggered by underground technological impacts; Luis Cueto-Felgueroso: Numerical modeling of injection-induced earthquakes in poroelastic media using laboratory-derived friction laws; Sander Osinga: Characterization of magnitude distributions in induced seismicity settings; Matthew Weingarten: Coupling physics-based forecasting and optimization models for induced seismicity mitigation: a case study from the Raton Basin, USA; Sergio Vinciguerra: Using AE based Machine Learning Approaches to Forecast Rupture during Rock Deformation Laboratory Experiments.-- Session 5 Case Studies of induced seismicity: Peter Meier: Status of the learning curve since Basel from the perspective of a project developer; Mateo Acosta: On the need to account for fault strength excess and time-dependent nucleation to model and forecast induced seismicity; Víctor Vilarrasa: Castor undergound gas storage project: lessons learnt to avoid project cancellation by induced seismicity; Grzegorz Kwiatek: Factors characterizing stable seismic energy release during hydraulic stimulations: EGS Helsinki and experimental perspective; Callum Harrison: Moment Tensor Inversion of Microseismicity at the United Downs Deep Geothermal Project, Cornwall; Jin-Han Ree: The 2017 MW 5.4 Pohang ‘triggered’ earthquake and updates; Iman Vaezi: Irreversible strain elucidates microseismicity source mechanisms: Hydroshearing simulation in fractured crystalline rock at BedrettoLab; Martina Rosskopf: Analyzing induced seismicity and their source characteristics during hydraulic stimulations inthe Bedretto Underground Laboratory; Bettina Goertz-Allmann: The value of microseismic in practical applications of CCS monitoring; Linus Walter: Forecasting the Temporal Evolution of Induced Seismicity at the Illinois Basing Decatur Project via Random Forest Model; Yuliia Semenova: Ground Seismic Response Analysis of the Decatur, Ill., CO2 sequestration demonstration site; Germán Rodríguez-Pradilla: Quantifying the variability in fault density across the UK Bowland Shale, with implications for CCS-induced seismicity hazard in the UK Continental Shelf; Sara Hanson-Hedgecock: Probabilistic Data Fusion for Evaluating Induced Seismic Hazards in Enhanced Geothermal Systems; Closing of the workshop: Víctor Vilarrasa (CSIC).-- Poster sessions; Antony Butcher Induced and Tectonic Seismic Characterisation using Downhole Recordings from Cornwall, UK; Gemma Maria Cipressi A methodological approach to characterize seismicity induced by geofluids; Yusuke Mukuhira Machine learning multivariate analysis for injection-induced seismicity risk evaluation; Haiqing Wu Stochastic poromechanical analysis of induced seismicity – application to the Pohang Mw 5.5 earthquake; Auregan Boyet Forecasting induced seismicity to investigate the most convenient strategy for injection and cessation of injection; Iman Vaezi Implicit Modeling of a Single Fracture Using a Continuum Equivalent Layer for Simulating Coupled Processes; Víctor Vilarrasa GEoREST: predictinG EaRthquakES induced by fluid injecTion; Tian Guo Reducing Subsurface Uncertainty with a Machine Learning Model Based on Ground Deformation Measurement; Zhen Xu Strategy for Evaluating Coupled THMC Processes during Underground Hydrogen Storage; Sanchit Sachdeva Fault Stability and Induced Seismicity Under Cycle Injection and Production of H2., Peer reviewed

This software computes the diffusion of fluid pressure p(x,t) in a 1D domain based on the concept of Physics Informed Neural Networks (PINN) for a heterogeneous modeling domain., Field-data assimilation to calibrate rock properties in numerical physics-based reservoir models of hydrogeological applications is challenging. Recently, Artificial Neural Networks (ANN) have emerged as a promising alternative to handle noisy data seamlessly. However, in hydrogeology, even though data are abundant over time, observation wells are sparse over space, which results in insufficient data to train ANN. Here, we propose Physics-Informed Neural Networks (PINN) to bridge the gap of sparse spatial data by imposing physical conditions. We test ANN and PINN on a synthetic dataset for fluid pressure diffusion p(x,t) through a low-permeable porous medium that hosts a high-permeability equivalent fracture material. By comparing the ANN and the PINN as a function of the number of observation wells, we find that the PINN model outperforms the ANN when having less than 14 wells. Adding noise to the training data reveals the advantage of PINN to be more robust for random measurement errors or ambient noise. We finally test the applicability and limitations of PINN to represent fractures as a thin equivalent material while having no observations inside the domain and find that accuracy can be maintained when reducing the thickness of the equivalent material at the expense of increasing the computation time. Given that hydrogeological applications count with a limited number of observation wells, PINN appears as a more suitable machine learning tool than purely data-driven ANN for reservoir modeling. Therefore, we consider this work a starting point for developing more realistic reservoir models with heterogeneous material distribution based on the PINN architecture., LW acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under Grant Agreement No. 801809., Peer reviewed

Induced seismicity poses a challenge to the development of Enhanced Geothermal Systems (EGS). Improving monitoring and forecasting techniques is essential to mitigate induced seismicity and thereby fostering a positive perception of EGS projects among local authorities and population. Induced seismicity is the result of complex and coupled thermo-hydro-mechanical-chemical mechanisms. Injection flux and pressure are crucial controlling parameters for both hydraulic stimulation and circulation protocols. We develop a methodology combining a hydro-mechanical model with a seismicity rate model to estimate the magnitude and frequency of mainshocks and aftershocks induced by fluid injection. We apply the methodology to the case of the Basel EGS (2006, Switzerland) to compare the effects of progressive, cyclic and constant injections on the mechanical response of discrete faults. Results from the coupled hydro-mechanical models show that the pore pressure diffusion and consequent enhancement of fault permeability are limited to the vicinity of the injection well during cyclic injection. Additionally, constant injection induces seismicity from the start of the injection but enhances the permeability of most of the faults within a shorter duration, inducing less post-injection seismicity. The methodology can be adapted to any numerical model and allows new projects to be developed by anticipating the safest injection protocol.This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'., A.B. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) under grant agreement no. 801809. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, grant CEX2018-000794-S funded by MICIU/AEI/ 10.13039/501100011033). IMEDEA is an accredited ‘Maria de Maeztu Excellence Unit’ (grant CEX2021-001198, funded by MICIU/AEI/10.13039/501100011033). S.D.S. acknowledges the support of the MICIU /AEI /10.13039/501100011033 and the European Union “Next Generation EU”//PRTR and the Spanish Ministry of Science and Innovation” through the ‘Ramón y Cajal’ fellowshipgrant (reference RYC2021-032780-I). Additional funding was provided to J.R. by the U.S. Department of Energy under contract No. DE-AC0205CH11231 to the Lawrence Berkeley National Laboratory., Peer reviewed

This dataset includes the input files of the numerical models used in the manuscript for simulating the injection well and the horizontal wells of the Closed Loop Geothermal System (CLGS) setup. There are two main folders named Vertical and Horizontal that contain their respective models. In each of these folders, several subfolders represent models with different flow rates (4 in Vertical and 14 in total from the horizontal models). In each of the subfolders, there are the models with files ending with “_gen.dat” containing the input data of the model, including material properties, initial and boundary conditions and the time intervals. There are also files ending with “_gri.dat” that include information on the mesh. The file “root.dat” includes the name of the model., European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu), under grant agreement No. 801809. IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MCIN/AEI/10.13039/501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198)., Peer reviewed

Fractures control fluid flow, solute transport, and mechanical deformation in crystalline media. They can be modeled numerically either explicitly or implicitly via an equivalent continuum. The implicit framework implies lower computational cost and complexity. However, upscaling heterogeneous fracture properties for its implicit representation as an equivalent fracture layer remains an open question. In this study, we propose an approach, the Equivalent Fracture Layer (EFL), for the implicit representation of fractures surrounded by low-permeability rock matrix to accurately simulate hydromechanical coupled processes. The approach assimilates fractures as equivalent continua with a manageable scale (≫1 μm) that facilitates spatial discretization, even for large-scale models including multiple fractures. Simulation results demonstrate that a relatively thick equivalent continuum layer (in the order of cm) can represent a fracture (with aperture in the order of μm) and accurately reproduce the hydromechanical behavior (i.e., fluid flow and deformation/stress behavior). There is an upper bound restriction due to the Young's modulus because the equivalent fracture layer should have a lower Young's modulus than that of the surrounding matrix. To validate the approach, we model a hydraulic stimulation carried out at the Bedretto Underground Laboratory for Geosciences and Geoenergies in Switzerland by comparing numerical results against measured data. The method further improves the ability and simplicity of continuum methods to represent fractures in fractured media., I.V. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (
www.georest.eu
), under grant agreement No. 801809. J.C. and V.V. acknowledge financial support from the “ZoDrEx” project, which has been subsidized through the ERANET Cofund GEOTHERMICA (Project no. 731117), from the European Commission and the Spanish Ministry of Economy, Industry and Competitiveness (MINECO). The work of Geo-Energie Suisse AG was financially supported by the Swiss Federal Office of Energy within the framework of the ZoDrEx GEOTHERMICA project under contract SI/501720-01. F. P. acknowledges funding from the European Union's Horizon 2020 Research and Innovation Program through the Marie Sklowdowska-Curie Individual Fellowship ARMISTICE, Spain under Grant Agreement No. 882733. K.Y. acknowledges funding from EURAD, the European Joint Programme on Radioactive Waste Management through the project DONUT (Grant No
847593
). IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant
CEX2021-001198
, funded by MCIN/AEI/10.13039/501100011033). IDAEA-CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S)., Peer reviewed

V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu) under grant agreement No. 801809. A.V. acknowledges funding from Spanish Ministry of Science and Innovation grant CGL2017-88864-R. IDAEA-CSIC and ICM-CSIC are Centres of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation Grants CEX2018-000794-S and CEX2019-000928-S, respectively, funded by MCIN/AEI/ 10.13039/501100011033)., Peer Reviewed

Geologic carbon storage, as well as other geo-energy applications, such as geothermal energy, seasonal natural gas storage and subsurface energy storage imply fluid injection and/or extraction that causes changes in rock stress field and may induce (micro)seismicity. If felt, seismicity has a negative effect on public perception and may jeopardize wellbore stability and damage infrastructure. Thus, induced earthquakes should be minimized to successfully deploy geo-energies. However, numerous processes may trigger induced seismicity, which contribute to making it complex and translates into a limited forecast ability of current predictive models. We review the triggering mechanisms of induced seismicity. Specifically, we analyze (1) the impact of pore pressure evolution and the effect that properties of the injected fluid have on fracture and/or fault stability; (2) non-isothermal effects caused by the fact that the injected fluid usually reaches the injection formation at a lower temperature than that of the rock, inducing rock contraction, thermal stress reduction and stress redistribution around the cooled region; (3) local stress changes induced when low-permeability faults cross the injection formation, which may reduce their stability and eventually cause fault reactivation; (4) stress transfer caused by seismic or aseismic slip; and (5) geochemical effects, which may be especially relevant in carbonate-containing formations. We also review characterization techniques developed by the authors to reduce the uncertainty in rock properties and subsurface heterogeneity both for the screening of injection sites and for the operation of projects. Based on the review, we propose a methodology based on proper site characterization, monitoring and pressure management to minimize induced seismicity., Peer Reviewed