This session is dedicated to studies investigating some of these THMC interactions by means of mathematical, experimental, numerical, data-driven and artificial intelligence methods, as well as studies focused on laboratory characterization and on gathering and interpreting in-situ geological and geophysical evidence of the multi-physical behavior of rocks. Welcomed contributions include approaches covering applications of carbon capture and storage (CCS), geothermal systems, gas storage, energy storage, mining, reservoir management, reservoir stimulation, fluid injection-induced seismicity and radioactive waste storage.
Orals: Fri, 8 May, 14:00–18:00 | Room -2.43
Induced seismicity, that is, seismicity associated with subsurface operations, has been reported over the last 50 years in different sites world-wide. The knowledge gained from those empirical case studies have helped to pinpoint the main co-factors leading to fault instability, being related to the tectonic stress state of the reservoir, its local geology, induced pore pressure and thermo-chemical changes, local stress redistribution from event-event interactions and feedback from (a)seimic slip on faults. Despite the progress made, forecasting of the induced seismic risk during each stage of a reservoir project remains a challenge. Studies relying on classical earthquake catalogue parameters, which are fed into advanced traffic light system (ATLs) have been partly successful in linking the seismic risk to operational parameters. However, these datasets are generally „biased“ toward more energetic sequences (i.e. few high magnitude events) and are limited by the highly variable quality of operational data available for each particular site. A growing number of field studies (e.g. the Mw5.5 Pohang earthquake, the Mw3.9 Strasbourg earthquake) have been challenging the general validity of usually adopted log-linear frequency-magnitude correlation statistics, thereby calling for a critical revision of our current understanding of the dynamics leading to induced earthquakes.
In this contribution, we will discuss how integrating information derived from physics-based quantitative models into existing stochastic frameworks can help to overcome the shortcomings of purely statistical approaches to induced seismicity.
We will dedicate a first part of this contribution to showcase via diverse field and laboratory examples how physics-based models can be effective to improve our understanding of structure-property relationships under transient loading and across-scale, and to discriminate intrinsic spatio-temporal footprints of the driving dynamics leading to induced earthquakes including expected magnitudes, their spatial and temporal distribution with respect to site-specific conditions and operational parameters. We will then open a second chapter where we will discuss how front ending these software solutions to existing state-of-the-art HPC platforms can enable near real-time model calibration and to additionally explore the sensitivity in terms of either reservoir performance and/or induced seismicity to a wide spectrum of reservoir parameters therefore outperforming classical forecasting models based on field data alone. We will then conclude with an open discussion on how these hybrid approaches can benefit from novel methods from the field of artificial intelligence and machine learning and where existing knowledge gaps remain.
How to cite: Cacace, M., Blöcher, G., Degen, D., Hofmann, H., Scheck-Wenderoth, M., and Schmittbuhl, J.: Physics-based and probabilistic modelling of induced seismicity: where we stand and where to go next, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2592, https://doi.org/10.5194/egusphere-egu26-2592, 2026.
Injection-induced seismicity is commonly attributed to fluid diffusion, poroelastic stress transfer, and stress loading associated with aseismic creep. In deep geothermal systems, thermal stresses generated by fluid–rock heat exchange constitute an additional mechanism that may significantly influence seismicity. Modeling studies suggest that pore pressure diffusion plays a dominant role in fault reactivation during the early stages of geothermal operations (months to a few years), whereas the contribution of thermal stress may become significant over longer timescales (years to decades). However, the relative contributions of these triggering mechanisms in both aseismic and seismic fault reactivation remain poorly constrained, and the influence of fault properties and operational strategies is still largely unexplored.
In this work, we investigate how thermal stress changes drive aseismic and seismic fault reactivation, as well as their contribution relative to pore pressure and poroelastic stress redistribution. We introduce the effective normal and shear stress changes calculated from a 3D Thermo-Hydro-Mechanical (THM) model into a 3D fault slip sequence model in the rate-and-state frictional framework to simulate fault slip responses to geothermal operation scenarios. We explore two background fault slip scenarios, a seismically active fault undergoing multiple seismic cycles, and a fault that accommodates periodically recurring aseismic deformation.
Overall, our results indicate that the timing of stress perturbation relative to the background slip cycle exerts the primary influence on clock advance of both aseismic and seismic fault slip behaviour during injection operations. All model configurations and variations in the timing of applied stress perturbations lead to an initially aseismic response in both the seismic and aseismic faulting scenarios. However, in the seismic-cycle scenario, aseismic slip accelerates to seismic slip within the injection period when perturbations are introduced late in the background seismic cycle, that is, when the fault is already close to failure. The aseismic-cycle scenario exhibits similar behaviour under conditions where the fault experiences a substantially larger (a factor of 2) stress perturbation. Pore pressure changes preferentially control both the timing and extent of coseismic fault rupture, primarily due to the larger spatial region over which they affect the fault plane. Thermal stress changes are significant in magnitude, yet they exert a comparatively minor influence on the overall aseismic and coseismic slip distribution on the fault because of the limited extent of the fault surface over which they act.
From an operational perspective, we find that cyclic injections generate larger pore-pressure changes compared to a constant injection rate, which may promote earlier seismic reactivation or facilitate a transition from aseismic to seismic slip during the injection period. Finally, our results suggest that a simple doublet configuration could significantly reduce the risk of seismic fault reactivation during injection and production. In such cases, fault architecture (conduit vs. barrier) and relative positioning of injection and production wells play a critical role.
How to cite: Verdecchia, A., Liu, Y., and Harrington, R.: Modeling seismic and aseismic fault reactivation in deep geothermal systems: impacts of pore-pressure, poroelastic, and thermal stresses., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9241, https://doi.org/10.5194/egusphere-egu26-9241, 2026.
Significant surface vertical displacements, with a maximum of 5 cm, were observed near the Geothermal Power Plant of Landau, Germany, between 2013 and 2014. These vertical movements are associated with a leakage in the casing of the reinjection well at depths between 479 m and 751 m, corresponding to an uncemented section of the well. The leakage resulted from an injection of hot water into the subsurface, inducing coupled thermo-hydro-mechanical (THM) processes and ground surface uplift. While the contribution of hydraulic effects has been investigated in similar cases, the role of the thermal effects has been less explored. We have studied the Landau case by developing a new analytical solution to estimate ground surface vertical displacements that accounts for the effects of both hydraulic head and temperature changes. We have verified this solution with THM numerical models and real data measurements (levelling and PS-INSAR).
This work was financed by the ERANET project HEATSTORE (170153-4401). This project has been subsidized through the ERANET cofund GEOTHERMICA (Project n. 731117), from the European Commission, RVO (the Netherlands), DETEC (Switzerland), FZJ-PTJ (Germany), ADEME (France), EUDP (Denmark), Rannis (Iceland), VEA (Belgium), FRCT (Portugal), and MINECO (Spain). Also, the first author is supported by a grant from the Department of Research and Universities of the Generalitat de Catalunya (2023 FI-3 00208). S.D.S. acknowledges the support of the ‘Ramón y Cajal’ fellowship (reference RYC2021-032780-I) funded by MICIU /AEI /10.13039/501100011033 and by "European Union Next Generation EU/PRTR", and that from the HydroPoreII project (reference PID2022-137652NB-C44) funded by MICIU /AEI/ 10.13039/501100011033 and by “ERDF, EU”.
How to cite: Vidal, R., De Simone, S., Saaltink, M. W., and Olivella, S.: Thermo-hydro-mechanical effects of a well leakage near the Geothermal Power Plant of Landau, Germany, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1687, https://doi.org/10.5194/egusphere-egu26-1687, 2026.
Geothermal systems in the Taupō Volcanic Zone (TVZ), New Zealand, are sustained by large-scale convection of groundwater that is mainly confined to the brittle upper crust. The depth and temperature of the brittle–ductile transition (BDT) is hypothesised to demarcate the lower boundary of fracture-hosted permeability and hence fluid circulation. Thus, we expect the thermal structure of the convection cells, both at their base and the geothermal resource at drillable depths, to be influenced by the BDT temperature. As direct observations below 3 km are difficult to obtain, the objective of this study is to test whether temperatures in the upper 2 km of hydrothermal systems are correlated with BDT temperature and could hence serve as a proxy constraint on deep thermal and permeability structure.
This work uses numerical models of hydrothermal circulation that couple Darcy flow and heat transport in a 2D axisymmetric domain. The models assume a deep basal “hotplate” of 800 to 1300°C at 15 km depth and then allows the permeable domain to be dynamically determined as a function of temperature. Following the work of Hayba & Ingebritsen (1997) and Scott et al. (2016), we use a logistic/sigmoid model of rock permeability that decreases smoothly across a prescribed BDT temperature range and whose mid-point temperature was varied between 350 and 650°C. The models reproduce the expected dominance of fluid convection at shallow depths where temperatures are sufficiently low to not inhibit permeability. A convective-conductive boundary forms at a depth that is self-determined by the system balance between shallow convective and deep conductive heat transfer.
Analysis across a range of model parameters and anisotropy conditions confirms a correspondence between the rock’s BDT temperature range and hydrothermal fluid temperatures at 2 km depth. Across a range of BDT temperatures and anisotropy assumptions, we recover a linear relationship between the hydrothermal upflow temperature at 2 km depth and the applied BDT temperature (e.g., 338°C at 2 km depth corresponding to a 400–500°C BDT range). Modelled convection cells range in power outputs from 60 to 285 MW, which is consistent with the range of estimates for TVZ geothermal fields. These findings suggest that shallow temperature observations can be used to infer rock rheology and permeability properties in hydrothermal provinces.
How to cite: Banerjee, D., Dempsey, D., Kennedy, B., Cater, J., Hewett, J., and Cusack, D.: Modelling the Signatures of Supercritical Geothermal Resources under Thermally-Inhibited Permeability Constraints, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6120, https://doi.org/10.5194/egusphere-egu26-6120, 2026.
The Yangyi geothermal field in central Tibet represents a structurally controlled high-temperature geothermal system that has been extensively investigated through geological, geochemical and geophysical exploration, resulting in a substantial body of multi-source datasets. Despite this wealth of information, previous studies have predominantly addressed individual methods or limited spatial scales, and a unified framework for interpreting reservoir architecture, fluid migration pathways, and spatial heterogeneity has remained absent.
To address this limitation, this study integrates geological mapping, gravity and magnetotelluric surveys, borehole logging and well testing, together with short- and long-term tracer experiments, to construct a three-dimensional geological model of the Yangyi geothermal system within a consistent spatial framework. The model explicitly incorporates the major fault systems, deep and shallow stratifications constrained by the basement andesite layer, and the spatial distribution of low-resistivity zones. Productive geothermal wells, including ZK203, ZK208, and ZK403, are used to constrain the relationships between structural elements and observed hydraulic responses.
The results demonstrate that the spatial zonation of the Yangyi geothermal field is primarily governed by fault-controlled vertical structural differentiation. Shallow fracture networks spatially coincide with low-resistivity zones and constitute hydraulically efficient pathways that facilitate rapid tracer migration between wells. In contrast, the contribution of deep thermal fluids is mainly regulated by major fault structures and is progressively modified along structurally guided flow paths. Integrated geological, geophysical, and tracer evidence indicates that the parent geothermal fluid originates from deeply circulating meteoric water, ascending at depth predominantly along the F5 fault and migrating upward at shallower levels preferentially along the F3 fault. The development of low-resistivity zones reflects fracture enhancement and hydrothermal alteration within the shallow structural domain during this upflow process.
By integrating multi-source datasets within a three-dimensional geological modeling framework, this study provides a coherent structural interpretation for the coexistence of reservoir zonation and inter-well hydraulic connectivity in the Yangyi geothermal field, and offers robust structural constraints for identifying favorable reservoir configurations in fault-controlled geothermal systems.
How to cite: Zhai, H., Kolditz, O., and Shao, H.: A Three-Dimensional Conceptual Model of the Yangyi Geothermal Reservoir Based on Integrated Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12120, https://doi.org/10.5194/egusphere-egu26-12120, 2026.
Underground gas storage is increasingly considered for renewable-based hydrogen as part of the energy transition. However, hydrogen has a much lower energy density than methane, requiring significantly larger injected volumes to deliver the same stored energy. The geomechanical consequences of this difference remain largely unexplored.
We investigate the impact of replacing methane with hydrogen on subsurface stress conditions and caprock integrity using a coupled two-phase flow and geomechanical model of a dome-shaped aquifer in northern Spain. Five years of seasonal storage cycles are simulated for both gases under equivalent energy storage conditions. Changes in pore pressure and stress are evaluated using the Mohr–Coulomb failure criterion.
Results show that hydrogen storage induces larger pore-pressure increases, leading to a stronger reduction in effective stress and higher mobilized friction coefficients compared to methane. In several areas, hydrogen storage approaches commonly adopted stability thresholds, whereas methane storage remains mechanically stable. These findings emphasize the need for dedicated geomechanical assessments when transitioning from methane to underground hydrogen storage.
Acknowledgments
This research was supported by the ‘‘Ministerio de Ciencia, Innovación y Universidades’’, Spain and ‘‘Agencia Estatal de Investigación’’, Spain (10.13039/501100011033) and by ‘‘ERDF/EU’’, through grant HydroPore II (PID2022-137652NB-C43).
How to cite: Bastias, J., Cueto-Felgueroso, L., and Santillán, D.: Contrasting the Formation Integrity and Geomechanical Response of Underground Methane and Hydrogen Storage at Equivalent Energy Density, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17991, https://doi.org/10.5194/egusphere-egu26-17991, 2026.
Underground hydrogen storage (UHS) in porous media reservoirs is increasingly being considered as a means to balance the intermittency of renewable energy systems. However, the geomechanical risks associated with the cyclic injection and production of hydrogen remain underexplored compared to compressed air energy storage (CAES) and the storage of more viscous gases, such as CO₂ and CH₄. This study employs coupled hydro-mechanical numerical simulations of a sandstone reservoir bounded by shale caprock and underburden, intersected by a steeply dipping fault, and overlain by an upper aquifer. We compare deformation, fluid migration, and leakage risks between hydrogen and compressed air under identical cyclic injection scenarios using an integrated workflow that combines a stress-dependent Barton-Bandis caprock fracturing model with a Coulomb friction-based fault permeability evolution model.
Our results reveal that both hydrogen and compressed air follow similar failure sequences: injection-induced pressure buildup triggers caprock failure, followed by gas migration into the caprock and subsequent fault activation. However, critical differences emerge in timing and magnitude. In UHS, leakage into the caprock and overlying aquifer initiates much earlier in the injection cycle compared to CAES. Furthermore, hydrogen consistently results in substantially higher cumulative leakage volumes and generates larger magnitudes of surface uplift and subsidence. This amplified surface deformation is driven by stronger pressure perturbations and a more vertically extensive gas plume, a direct consequence of hydrogen’s high mobility.
These findings suggest that hydrogen compromises reservoir geomechanical integrity faster than compressed air. Since CAES fluids are already less viscous than CH₄ or CO₂, the containment challenges identified here for hydrogen are more severe than other underground gas storage systems. Our findings reveal that site-selection and integrity criteria for CAES, CO₂, or CH₄ storage are inadequate for UHS. UHS requires revised caprock permeability thresholds and enhanced leak detection strategies (such as real-time fault and surface monitoring) to ensure safer operations and infrastructure repurposing from depleted fields.
How to cite: Talukdar, M., Ismayilov, M., and Jha, B.: Hydrogen Storage Induces Earlier Leakage and Greater Surface Deformation Compared to Compressed Air and Viscous Gases, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18451, https://doi.org/10.5194/egusphere-egu26-18451, 2026.
Carbon capture and sequestration (CCS) is one of the key geo-energy solutions essential to mitigate the acceleration of climate change. Presence of a secure caprock formation that serves as a seal for injected CO2 – such as a low permeability shale – is vital for ensuring safe long-term storage of CO2. The effectiveness of a seal is controlled by its petrophysical properties which can change due to compaction, diagenesis and the in-situ stress field. The geological history and the changing stress field could reduce the caprock’s effectiveness as a flow barrier, by enabling localized migration through the primary seal, leakage along faults and fractures, or diffusive flow through the rock system. However, the relative effect of associated processes on CO2 migration is difficult to investigate individually due to the complexity of the interactions that may require modelling of coupled processes. Faults and fractures are common in geological formations and may act as conduits for flow. Over the course of injection and storage, reactivation or closure of pre-existing discontinuities or injection-induced microfractures may occur.
In this paper, we assess the conditions for CO2 migration through a shale layer by investigating end-member scenarios to improve the accuracy of simulations of the complex physical and chemical interactions involved. A reservoir-caprock system model, based on the 2019 Sleipner Benchmark dataset, was utilized with implementation of regionally determined petrophysical parameters to evaluate the effects of different conditions for CO2 migration. We generated two-phase flow models with inclusion of the effects of capillary pressure and relative permeability appropriate for the Utsira sand and intra-reservoir shales. By using PFLOTRAN, we have simulated a hypothetical fault with high resolution gridding to evaluate the criteria which are likely to control flow through a faulted caprock.
The results demonstrate how a CO2 plume with realistic buoyancy pressure only migrates along fracture zones of relatively high effective permeability (affected by fracture width), while lower permeability fractures (1 mD and below) act as a capillary barrier to two phase flow. Comparison with the latest insights into the actual migration routes at Sleipner, based on Full-Waveform Imaging, allows us to infer the outer bounds for properties of faults that have acted as CO2 migration pathways at Sleipner.
How to cite: Yun, T. K., Ringrose, P., and Berg, C. F.: Assessing Conditions for CO2 migration through a fractured shale, inspired by Sleipner, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10621, https://doi.org/10.5194/egusphere-egu26-10621, 2026.
Clay–rich formations are widely regarded as effective caprocks for geological CO2 storage; however, the presence of fractures in fault zone introduces significant uncertainty regarding their hydraulic behaviour during injection. In such settings, fluid migration is expected to be largely governed by fracture networks, while coupled hydraulic and geochemical processes associated with CO2–water–rock interactions may progressively modify hydraulic properties over time. This study presents a reactive transport modelling investigation of the CS–D (Carbon Sequestration – Series D) in situ CO2 injection experiment, with the aim of quantifying fracture hydraulic behaviour within a faulted clay–rich caprock.
A three-dimensional reactive transport model has been fully implemented using HYTEC to simulate coupled fluid flow and CO2–water–rock interactions within a fractured fault zone embedded in a low-permeability clay matrix. The modelling framework accounts for aqueous speciation, mineral dissolution and precipitation, as well as advective–diffusive transport, and is configured to reproduce the experimental conditions of the CS–D test. Structural and hydrogeochemical observations derived from the experiment are used to constrain boundary conditions and initial states, while fracture hydraulic properties are treated as key uncertain parameters.
The numerical framework enables a systematic investigation of the sensitivity of pressure evolution and geochemical responses to variations in fracture permeability and reactive surface area. The current geometric representation captures the principal structural characteristics of the faulted zone and retains sufficient flexibility to explore alternative conceptual configurations as the analysis progresses. The present work addresses coupled hydraulic and geochemical processes and is intended to serve as a basis for future extensions towards a coupled thermo-hydro-mechanical-chemical (THMC) framework relevant to subsurface energy applications.
The resulting simulations are expected to provide quantitative constraints on the range of fracture hydraulic properties compatible with the hydraulic and geochemical signals observed during CO2 injection. Ultimately, this study seeks to improve the process-based understanding of fracture-controlled flow in faulted clay-rich caprocks and to support the interpretation of in situ experiments relevant to the long-term integrity and safety of geological CO2 storage and related geo-energy technologies.
How to cite: Koç, Ü., Corvisier, J., Bruel, D., and Blanco-Martín, L.: Coupled Hydraulic-Geochemical Processes in a Faulted Clay-Rich Caprock: Reactive Transport Modelling of an In Situ CO2 Injection Experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11403, https://doi.org/10.5194/egusphere-egu26-11403, 2026.
Hydraulic stimulation is a key technique in Enhanced Geothermal Systems (EGS) to enhance reservoir permeability, but it may also induce fault reactivation and seismicity. Understanding the coupled hydro-mechanical (HM) processes governing fluid pressure diffusion and rock deformation is therefore essential for reservoir optimization and seismic risk mitigation. In this context, validated and well-calibrated numerical models provide a cost-effective alternative to repeated field experiments, enabling the investigation of different stimulation scenarios.
In this study, we develop and validate a three-dimensional HM framework in COMSOL where the fractures and fault zone are described by an elstopaltsic constitutive model using data from the Bedretto Underground Laboratory (BedrettoLab). The model is applied to the hydraulic stimulation experiment conducted during VALTER Phase 1, where a discrete fault is explicitly represented. Model accuracy is evaluated by comparing simulated pressure and strain responses with observations from nearby monitoring wells, allowing us to assess the model’s ability to reproduce hydromechanical behaviour during injection.
To further investigate the experiment, we conduct a sensitivity analysis on key hydraulic and mechanical parameters, injection scenarios, and fault and fracture geometries. This analysis is used to explore the potential role of fracture networks surrounding the main fault and their influence on the system’s hydromechanical response.
How to cite: Khezri, K., Jahangir, E., Abuaisha, M., Bruel, D., Clasen Repollés, V., Pio Rinaldi, A., and team, B.: Numerical Investigation of Hydro-Mechanical Processes During Hydraulic Stimulation at BedrettoLab, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13160, https://doi.org/10.5194/egusphere-egu26-13160, 2026.
The implementation of an artificial impermeable overlying boundary has been proven to enhance recovery efficiency and prevent methane leakage during marine natural gas hydrate extraction. However, traditional methods such as lurry, gel, or CO2 hydrate injection can cause irreversible damage to the marine ecosystem, and prevent effective recovery of the materials used. To overcome these drawbacks, this study proposes the construction of a frozen barrier in the overlying layer of marine gas hydrates, to suppress methane leakage, strengthen the overlying sediments, and prevent seawater intrusion. This approach avoids ecological damage, and ensures seabed strata resilience. Experimental results show that the critical temperature for frozen barrier formation is -3 ℃, this effectively prevents the infiltration of pore fluids under actual marine conditions. The effects of the barrier’s freezing temperature and range on the gas production rate are numerically analysed, and simulation results show that the presence of the frozen barrier enhances the depressurization effect, thereby increasing the production rate by 18.67 %. When the frozen barrier range is 60 m, the hydrate dissociation rate increases by 24.67 %, and cumulative gas production rises by 24.41 %.
How to cite: Wang, Y., Lei, J., and Dai, C.: Freeze barrier enhanced depressurization of hydrate exploitation: An improved method for the permeability boundary of marine hydrates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2943, https://doi.org/10.5194/egusphere-egu26-2943, 2026.
Hydraulic fracturing, originally developed to enhance hydrocarbon production, is increasingly applied to geothermal systems, subsurface thermal energy storage, and carbon sequestration. In these applications, reservoir containment is critical: controlling fracture growth through careful management of injection pressure and flow rate is essential to prevent unintended fluid migration and ensure long-term caprock integrity. Hydraulic fracture growth is strongly influenced by near-tip processes, including rock breakage, viscous fluid flow within the fracture, and fluid exchange with the surrounding reservoir. In permeable, fluid-saturated formations, the mechanical response of the rock is coupled to pore pressure diffusion, giving rise to poroelastic phenomena such as additional normal stress acting on the fracture walls (backstress), which increases the fluid pressure required for propagation. This work investigates the near-tip region of a hydraulic fracture propagating in a homogeneous poroelastic medium to identify when poroelastic coupling significantly affects fracture opening and fluid pressure fields.
The near-tip region is modeled as a semi-infinite plane strain crack propagating at constant velocity in a linear isotropic poroelastic medium. Formulated in the moving tip reference frame, the problem is steady. Fracture propagation is governed by linear elastic fracture mechanics. We consider the two-dimensional nature of fluid exchange between the fracture and the surrounding reservoir, assuming the fracturing and pore fluids are identical Newtonian liquids. A fully coupled hydro-mechanical boundary integral formulation is developed. The model accounts for reciprocal poroelastic interactions: backstress generated by pore pressure diffusion in the surrounding rock and pore pressure perturbations induced by deformation of the solid skeleton. The resulting nonlinear system comprises boundary integral equations governing the normal stress along the fracture surfaces and the fluid pressure within the fracture, both dependent on the fracture opening and fluid exchange rate. The system is closed by the fracture propagation criterion and the lubrication equation for flow inside the fracture.
Analytical solutions are obtained for the near- and far-field regions. In the near-field, the fracture opening follows the square-root asymptote with drained elastic moduli, while the fluid pressure within the fracture is uniform. In contrast, the far-field is governed by the storage-viscosity asymptote with undrained elastic moduli. The solution bridging these regions is obtained numerically. Dimensional analysis shows that the problem is governed by four dimensionless coefficients: a dimensionless permeability, a dimensionless effective confining stress, a poroelastic stress coefficient, and a normalized difference between undrained and drained Poisson's ratios. Using parameter ranges representative of sandstone reservoirs, the fully coupled model is compared with reduced formulations that neglect reciprocal poroelastic interactions or retain only the backstress effect. We find that poroelastic effects intensify with increasing permeability and poroelastic stress coefficient, and as reservoir pressure approaches normal conditions, resulting in significant modifications of fracture opening and fluid pressure profiles. While backstress generally dominates deformation-induced pore pressure perturbations, the latter become pronounced in overpressured reservoirs during rapid fracture propagation. The results clarify the conditions under which fully coupled poroelastic interactions must be considered to accurately predict near-tip behavior, providing guidance for reliable modeling of hydraulic fracture propagation in poroelastic media.
How to cite: Kanin, E., Möri, A., Garagash, D., and Lecampion, B.: On the role of poroelasticity in the near-tip region of a hydraulic fracture, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18089, https://doi.org/10.5194/egusphere-egu26-18089, 2026.
Fracture mechanics has been mostly developed for elastic, brittle, dry materials, yet many subsurface geoenergy applications involve crack growth in porous rocks that are fluid-saturated. While the role of injected fluids in fracture propagation has been studied extensively, the contribution of pore fluids is still commonly treated indirectly. In most cases, pore fluid effects are ignored or absorbed into an apparent fracture resistance.
In fluid-saturated conditions, tensile fracture generates a localized dilation of the pore space ahead of the crack tip, which draws fluid inward from the surrounding pores. This results in a drop of pore pressure in this region, which reduces the effective stress applied to the skeleton, modifies the near-tip failure micromechanisms, and ultimately leads to a change of apparent fracture energy at the macroscopic scale. Up to now, these phenomena have been mostly predicted rather than observed, largely because pore-pressure transients are difficult to resolve at the spatial and temporal scales of crack propagation in the laboratory.
Here, we present a custom experimental platform designed to resolve pore-pressure transients during stable quasi-static crack propagation at prescribed velocity. We use a wedge splitting test (WST) in a water-filled triaxial pressurized cell. A miniature pressure sensor is embedded in the specimen provides real-time internal pore pressure measurements. Combining crack opening displacement, via digital image correlation, and applied force, using a force sensor, we infer the crack velocity and fracture energy throughout the test. We selected a class G oil well cement, with a homogeneous pore structure, low viscosity and well-controlled mechanical and hydraulic properties, as an analog material. In water-saturated conditions, its low permeability and high stiffness bring the characteristic poroelastic length scale ℓpe of pore-pressure variations into the micrometer-millimeter range for laboratory-accessible quasi-static crack speeds, for which spatiotemporal coupling becomes measurable.
Our measurements reveal a transient pressure drop that develops ahead of the crack front, whose magnitude scales with the square root of crack speed, consistent with poroelastic predictions. This underpressure reduces the near-tip effective stress, producing a fluid-induced toughening effect: the apparent fracture energy increases by up to a factor ~2 at the highest tested velocities. This toughening can be attributed to the contraction of the process zone, which leaves a measurable imprint on the fracture surface, revealed by white-light interferometry. Together, these findings identify ℓpe as a governing parameter for tensile rupture in saturated porous materials and motivate rate- and drainage-aware injection strategies for coupled hydro-mechanical processes in geo-energy settings.
How to cite: Lebihain, M., Guggisberg, A., Allache, M., Braun, P., and Violay, M.: Pore pressure at the crack tip: fluid-induced toughening during tensile fracture of fluid-saturated porous solids, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9104, https://doi.org/10.5194/egusphere-egu26-9104, 2026.
Natural hydrogen produced via serpentinization is emerging as a critical carbon-free energy source, yet the potential for induced seismicity governed by the interplay of mineralogical transformations and thermal anomalies remains poorly understood. To constrain the seismic hazard of natural hydrogen systems, we investigated the frictional stability of simulated fault gouges composed of olivine, lizardite, and their mixtures using a triaxial shear apparatus under hydrothermal conditions relevant to deep reservoirs (125 MPa confining pressure and temperatures of 100–300 °C). Our results reveal a complex competition between mineralogical composition and thermal conditions in controlling fault stability; while the coefficient of friction systematically decreases with increasing serpentinization degree (from ~0.7 for olivine to ~0.4 for lizardite), the velocity dependence parameter (a-b) exhibits a critical transition towards instability at elevated temperatures. Specifically, pure olivine transitions from velocity-strengthening to velocity-weakening behavior as temperature increases, and unexpectedly, lizardite—typically considered a stable sliding mineral—exhibits a distinct window of velocity-weakening behavior at ~250 °C. Furthermore, in mixed gouges (e.g., 50% serpentinization), temperature dominates over mineralogy, shifting the fault from stable sliding at 150 °C to potentially unstable slip at 250 °C. These findings suggest that the exothermic nature of serpentinization could drive fault systems into a velocity-weakening regime before complete serpentinization stabilizes the fault, implying that natural hydrogen exploitation carries a specific, thermally driven seismic risk that necessitates rigorous monitoring.
How to cite: Lv, J. and Zhang, F.: Frictional Stability Transition during Olivine Serpentinization: Implications for Induced Seismicity in Natural Hydrogen Systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13335, https://doi.org/10.5194/egusphere-egu26-13335, 2026.
The CO2 flow in deep saline reservoirs is controlled by different forces depending on the distance from the well. Far from the well, where capillary forces dominate, it is important to understand at which saturations the CO2 connects through the porous medium in order to better predict its migration within the reservoir.
We investigate CO2 breakthrough behaviour in Boise sandstone, a well-characterized porous reservoir analogue, using controlled laboratory-scale experiments on cylindrical core samples. A low uniaxial load (~5% UCS) was applied to the fully brine-saturated samples to maintain mechanical stability and acoustic sensor coupling. CO2 was injected at flow rates spanning the transition from capillary-controlled to Darcy-dominated flow regimes, ranging from 0.04–0.1 mln/min, and 5–80 mln/min, respectively. The CO2 breakthrough on the top of the setup was detected by using a portable and autonomous mass spectrometric system for on-site environmental gas quantification (“miniRuedi”) together with helium, nitrogen and water as background gases. The use of mass spectrometric detection allows for highly sensitive, real-time identification of CO2 breakthrough at very low concentrations, providing precise constraints on breakthrough timing and flow connectivity that cannot be resolved from pressure data alone. In addition, micro-CT scans before and after the experiments were made, showing the formation of microfractures.
The early experimental results show a clear correlation between the injection rate and breakthrough time, and the intensity of CO2, detected by the miniRuedi (Fig. 1). The observations highlight the role of pore structure in controlling CO2 migration pathways under capillary-dominated conditions, displaying the unsteady-state effects on the inlet pressure. The experimental setup proved to be highly responsive enabling the detection of small deviations within the system. These findings could contribute to improved understanding of pore-scale flow mechanisms relevant for safe and efficient geological CO2 storage and offer experimental constraints for numerical and upscaled flow models.
How to cite: Macut, M., Selvadurai, P., Madonna, C., Rinaldi, A. P., Zappone, A. S., Ringrose, P., and Berg, C. F.: Experimental Observation of CO2 Breakthrough in Boise Sandstone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13247, https://doi.org/10.5194/egusphere-egu26-13247, 2026.
Geological storage of CO₂ in basaltic formations enables permanent sequestration via in situ mineral carbonation, where CO₂‑rich fluids dissolve silicate minerals (e.g., basaltic glass, olivine), releasing divalent cations that react with dissolved inorganic carbon and precipitate as carbonate minerals such as calcite and magnesite. Basalts display highly heterogeneous pore networks and alteration textures, where fluid accessibility, reactive surface area, and mineralogy govern the location and rate of coupled dissolution–precipitation processes. The role of microstructure and micro-porosity in controlling mineralisation efficiency and rock property evolution remains poorly quantified. A better core-scale understanding of these features is required to optimise CO₂ injection strategies and interpretation of geophysical monitoring at pilot sites.
This work is an experimental investigation into CO₂-mineralisation in Icelandic basalts using X‑ray micro‑computed tomography (μCT) enhanced by contrast‑agents, and laboratory petrophysical measurements. Four Icelandic borehole cores with varying mineralogy, pore structure, and degrees of geothermal alteration were analysed. Sub‑samples from one core were exposed to CO₂‑rich brine for two months at 50 °C and 20–30 bar in a batch reactor, while in situ pH evolution was monitored to track bulk reaction progress. Before and after exposure, effective porosity, permeability, and P‑ and S‑wave velocities were acquired, enabling correlation between reaction progress, flow properties and acoustic response.
A novel multi‑tracer μCT workflow was developed to resolve fluid pathways and quantify sub‑resolution microporosity. Cylindrical core plugs (diameter and height ~6 mm) were scanned at a voxel size of ~2.45 μm. Using a time-lapse sequence of 3D volumes, we visualised pore network transport using three high-attenuation contrast agents: aqueous CsCl, NaI (1 mol/L), and gaseous Xenon. Difference imaging via the voxel-wise subtraction of baseline scans from contrast-filled states revealed advective and diffusive tracer invasion within vesicles, fractures, and the fine-grained matrix, demonstrating the respective accessibility of each tracer.
Microporosity was quantified using two complementary approaches. First, the discrepancy between μCT‑derived porosity and laboratory‑measured effective porosity was interpreted as accessible pore volume below the imaging resolution. Second, we utilise a partial-volume model where the relative increase in the attenuation of a single voxel, relative to the known attenuation of the pure tracer indicates the portion of the voxel filled, thereby providing an estimation of the sub-resolution microporosity. As a µCT-resolvable analogue for mineralisation-relevant cations (Ca²⁺, Mg²⁺), the CsCl tracer revealed preferential Cs+ uptake within zeolite channels in vesicular basalts. This spatial enrichment corroborates that zeolite-mediated cation exchange may facilitate carbonate precipitation at rates exceeding stoichiometric silicate dissolution (Alqahtani et al., 2025).
Post‑reaction μCT volumes show localised mineral precipitation, remobilisation of palagonite, and spatial correlation of new mineralisation with Fe–Ti oxides, suggesting they may serve as an additional iron source for carbonate growth. Measurable changes to mineralogy, porosity and acoustic velocities demonstrate how CO₂‑induced mineralisation modifies storage‑relevant properties at the core scale. Quantification of basaltic microporosity and improved understanding of transport behaviour can clarify mineralisation controls and help optimise future CO₂ injection strategies.
Alqahtani, A., Addassi, M., Hoteit, H., Oelkers, E., 2025. Rapid CO2 mineralization by zeolite via cation exchange. Sci. Rep. 15, 958. https://doi.org/10.1038/s41598-024-82520-6
How to cite: Annan, P., van der Net, A., Stavropoulou, E., Madonna, C., Rinaldi, A. P., and Zaponne, A.: Multi-Tracer µCT Characterisation of Basaltic Microporosity, Transport Visualisation, and Carbonation-Related Changes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13753, https://doi.org/10.5194/egusphere-egu26-13753, 2026.
Reactive flow, coupling transport and chemical alteration processes, is a key geological driver, taking place over a wide range of conditions and scales. In addition to natural phenomena (e.g., contact metamorphism; ore formation), many geo-energy technologies are also dependent on, or affected by reactive flow.
One well-studied example of reactive flow is the carbonation, alteration, and potential degradation of a typical wellbore cement exposed to a CO2-bearing fluid under reservoir conditions. As CO2 permeates the cement, it reacts with Ca2+ from portlandite and other cement gel phases to form CaCO3, leading to an increase in solid volume, and therefore a decrease in porosity (and permeability). Different experimental methodologies have been applied to better understand the progression of the carbonation front, including static exposure in batch apparatuses, and exposure to forced flow driven by a pressure gradient along the sample axis. However, progression of the carbonation front typically shows a dependence on the square root of time, suggesting that even under high pressure gradients, transport is still controlled by diffusion through the low-permeability matrix, rather than advective flow.
Interestingly, cement carbonation is often associated with a sharp reaction front, with large changes in mineral assemblage and fluid composition and pH across a relatively short distance. In this presentation, we take a closer look at the carbonation fronts in a set of cement samples exposed to wet supercritical CO2 and CO2-saturated water, using both batch and forced-flow methodologies. We will combine observations based on laboratory experiments with analytical and numerical modelling to address three closely related aspects of reactive transport. First, by explicitly evaluating the Peclet number, we demonstrate that diffusion dominates over advection under the tested conditions, providing a unified interpretation of batch and flow-through experiments. Second, we distinguish between the true diffusion coefficient of CO₂ in the pore fluid and the effective diffusion coefficient inferred from reaction-front propagation, showing that the latter is an emergent quantity controlled by reaction thermodynamics and concentration contrasts rather than a material property. Third, using a reactive transport model that couples fluid transport, solid-fluid reactions, and porosity evolution, we investigate the conditions under which sharp reaction fronts arise and contrast them with regimes that produce smooth transition zones.
How to cite: van Noort, R., Yarushina, V. M., and Schneider, Y. F.: Sharp reaction fronts during diffusion-dominated reactive flow. Experimental and numerical study using cement carbonation as example., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11767, https://doi.org/10.5194/egusphere-egu26-11767, 2026.
Subsurface storage and recovery of gas, carbon, heat, and water, key to the geoenergy transition, are governed by hydromechanical processes in the geologic medium. Despite the importance of hydromechanical storage, the physics of storage has received less attention than the physics of fluid flow. Storage is typically assumed to be a linear, homogeneous function of pore pressure. This approximation may hold for permeable unconsolidated formations under small hydraulic forcings but can break down in stiff or low-permeability media subjected to high-pressure injection and withdrawal.
One reason the physics of hydromechanical behavior in geologic reservoirs remains incomplete is the scarcity of local in-situ measurements of deformation during flow. Commonly available measurements, such as surface deformation (e.g., InSAR) or borehole displacement (e.g., extensiometers), vertically integrate formation strain. The advent of distributed fiber-optic sensing provides a new opportunity to resolve depth-dependent deformation in response to pressure variability.
I describe three experiments in which distributed strain was observed during fluid injection and withdrawal: (1) a sparsely fractured crystalline rock, (2) a semi-consolidated porous sandstone, and (3) a permeable aquifer. In all cases, fiber-optic distributed acoustic sensing (DAS) was used to measure along-wellbore deformation. The nanostrain sensitivity of DAS provided new insight into the physics of hydromechanical deformation associated with subsurface fluid movement. Displacement was vertically heterogeneous in all experiments, and storage parameters derived from displacement measurements were not directly comparable to those inferred from hydraulic responses. These results illustrate the need for coupled hydromechanical frameworks and in-situ measurements that jointly resolve fluid flow and deformation, particularly in the context of subsurface technologies central to the geoenergy transition.
How to cite: Becker, M. W.: Hydromechanical Storage Measured by Fiber Optic Distributed Acoustic Sensing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2221, https://doi.org/10.5194/egusphere-egu26-2221, 2026.
The signal-to-noise ratio (SNR) is a key parameter controlling the detectability, particularly for near-surface and shallow borehole seismic monitoring. While shallow borehole arrays are widely used to suppress surface noise and improve SNR, a physically consistent analytical description of SNR variation with depth has remained limited. Existing models typically assume an exponential decay of noise decay with depth and often neglect depth-dependent variations of the seismic signal itself. We developed a new analytical model describing the depth dependence of SNR in a homogeneous elastic half-space, explicitly accounting for the free-surface boundary condition. The signal is modelled as a superposition of upward- and downward-propagating body waves generated by reflection at the free surface. We modified already proposed noise model by Kalinichenko et al. (2025) that consistently links surface and shallow-borehole noise levels. The noise is represented as a superposition of an exponentially decaying surface-wave component and a slowly decaying body-wave component. We model depth dependence of noise as a superposition of exponentially decaying fundamental mode of surface waves and linearly decaying body waves. We show that the up- and down-going wave superposition results in frequency-dependent constructive and destructive interference of signal unsuitable for general microseismic monitoring. We show the depth of signal destructive interference, also known as a ghost, occurs also in a band-limited seismic signal and that its depth depends on the peak frequency of the signal. Furthermore, the complex SNR variations are limited to depths shallower than one-half of the wavelength of the peak frequency of the signal and SNR increases monotonically below this depth.
How to cite: Kalinichenko, O. and Eisner, L.: Depth Dependence of Signal-to-Noise Ratio in Shallow Seismic Monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19496, https://doi.org/10.5194/egusphere-egu26-19496, 2026.
Posters on site: Fri, 8 May, 10:45–12:30 | Hall X4
Marine clayey silt hydrate sediments are highly susceptible to fines migration during production, which strongly influences reservoir seepage behavior. Hydrate dissociation modifies pore structure and pore water salinity, triggering clay particle detachment, transport, and pore throat clogging. This study investigates pore-water-driven migration behaviors of illite and montmorillonite under hydrate depressurization, focusing on the coupled effects of flow rate, salinity, pore throat evolution, clay content, and production pressure. The results show that illite migrates preferentially ahead of silt particles and is controlled by distinct critical flow rate and salinity. Particle detachment is governed by torque imbalance induced by increasing flow rate. Salinity reduction exhibits a dual control mechanism: above the critical salinity, pore throat expansion associated with hydrate dissociation dominates illite migration, whereas below this value, thickening of the electric double layer and enhanced electrostatic repulsion markedly increase particle concentration, promoting clogging even at low flow rates. Migration mechanisms also depend on production pressure, shifting from flocculation-induced pore clogging at low pressures to bridging-dominated clogging at higher pressures. Montmorillonite exhibits a substantially stronger impact on seepage characteristics due to the combined effects of swelling, dispersion, and migration. Low salinity and high montmorillonite content significantly enhance particle availability, while low Reynolds number conditions favor rolling detachment, re-adsorption, and pore throat clogging. The results provide critical insights for optimizing hydrate production strategies and mitigating permeability damage and associated geohazard risks.
How to cite: Lei, J., Guo, W., and Wang, Y.: Migration characteristics of fine clay particles under the influence of pore water during production in marine clayey silt hydrate reservoirs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2937, https://doi.org/10.5194/egusphere-egu26-2937, 2026.
Ground deformation related to geo-energy activities is often caused by subsurface fluid injection and extraction, making reliable monitoring essential for understanding reservoir behavior and managing associated risks. Interferometric Synthetic Aperture Radar (InSAR) enables wide-area observation of surface deformation at millimeter scale, but deformation time series derived from a single satellite mission can be affected by coherence loss, atmospheric disturbances, and temporal gaps, particularly in environmentally complex regions.
In this study, we present a multi-sensor InSAR framework that integrates Sentinel-1 and TerraSAR-X data to improve deformation monitoring in geo-energy settings. The approach combines the dense temporal coverage of Sentinel-1 with the higher spatial resolution and phase stability of TerraSAR-X, allowing deformation signals to be captured more robust than with either sensor alone. After aligning the datasets in space and time, interferometric observations from both sensors are jointly analyzed to derive a unified deformation time series.
Deformation is estimated using a least-squares inversion strategy that accommodates uneven temporal sampling and overlapping observations from different sensors. Model-based residual analysis is used to assess data quality and identify potential artefacts, such as atmospheric effects or unwrapping errors, providing additional confidence in the deformation signals derived.
The combined analysis of Sentinel-1 and TerraSAR-X demonstrates the potential of multi-sensor InSAR to enhance temporal sampling and provide complementary information on surface deformation. While the integrated time series reveals improved continuity in certain periods, the results also expose limitations related to sensor differences and processing assumptions. These observations highlight both the opportunities and the challenges of multi-sensor InSAR fusion, and motivate further refinement of processing strategies to support more reliable deformation monitoring in geo-energy applications.
How to cite: Ramlie, M. C., Olea-Encina, P., Crosetto, M., and Monserrat, O.: Multi-Sensor Satellite Processing for the Monitoring of Geo-energies , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4916, https://doi.org/10.5194/egusphere-egu26-4916, 2026.
The natural gas hydrate reservoirs in the South China Sea are predominantly composed of argillaceous silt sediments, with the trial production area mainly consisting of fine-grained particles and clay minerals, notably montmorillonite and illite. The type and content of clay minerals directly influence the material composition and particle size distribution of the host sediments, thereby significantly affecting their mechanical properties. Furthermore, clay minerals exhibit pronounced plasticity, and their presence markedly alters the creep characteristics of the reservoir, exacerbating reservoir deformation and potentially leading to reservoir failure. Therefore, exploring the mechanism of clay minerals influence on the mechanical properties and creep behavior of hydrate deposits is an important basis for evaluating the stability of clayey silt reservoirs. Based on this background, this study deeply analyzes the influence of clay mineral type and content on the creep characteristics of clayey silt hydrate sediments to provide theoretical support for the safe exploitation of hydrates.
The failure strength of clayey silt hydrate-bearing sediments was obtained through experiments to determine the creep test conditions. Subsequently, the triaxial creep experiment under the stable presence of the hydrate was carried out to study the effects of clay mineral species and clay content on the creep characteristics of the sediments under different stress levels. The research results indicate that hydrate-bearing sediments containing montmorillonite exhibit greater initial and final deformation compared to those containing illite, and the creep rate of montmorillonite-bearing sediments is consistently higher than that of illite-bearing sediments. Clay content is negatively correlated with both sediment deformation and initial creep rate, and hydrate-bearing sediments with lower clay content require greater strain to achieve a constant creep rate. Stress level is positively correlated with sediment deformation and significantly influences the relationship between strain rate and strain. Montmorillonite-bearing hydrate sediments demonstrate stronger sensitivity to loading stress. Additionally, the long-term strength of hydrate-bearing sediments containing illite and montmorillonite at medium and low clay contents was determined.
Triaxial creep experiments were carried out to study the effects of clay mineral species, clay content and stress level on the creep characteristics of the silty silt sediment during hydrate decomposition. The results of the creep experiments during hydrate dissociation reveal that the creep strain and rate of montmorillonite-bearing sediments are generally higher than those of illite-bearing sediments, consistent with the deformation trends observed under stable hydrate conditions. For both illite- and montmorillonite-bearing hydrate sediments, the creep rate increases rapidly at the initial stage of the experiment and then decreases until it stabilizes in the later stage. As the illite content increases, the initial creep strain decreases, while the final creep strain increases. In montmorillonite-bearing sediments, both the initial and final creep strains increase with higher clay content. Additionally, an increase in clay content leads to a higher peak creep rate, particularly evident in montmorillonite-bearing sediments. With increasing stress levels, the initial and final strains of both types of sediments increase, with more pronounced changes in montmorillonite-bearing sediments. Under high stress levels, the peak creep rate increases, and a larger axial strain is required to achieve stability.
How to cite: Jia, R., Guo, W., Li, Y., and Tang, G.: Study on creep characteristics of clayey silt natural gas hydrate-bearing sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8604, https://doi.org/10.5194/egusphere-egu26-8604, 2026.
Oil shale is an extremely abundant geo-energy resource worldwide, capable of releasing oil and gas through heating above 350°C. In-situ pyrolysis conversion represents a crucial method for the utilization of oil shale resources; efforts are underway to verify its technical feasibility and economic viability at the reservoir scale. However, commercial development has not yet been realized, fundamentally due to an insufficient understanding of the complex multi-field coupling processes underground and the limitations of current in-situ pyrolysis conversion technologies. Through systematic research on the pyrolysis process of oil shale, the secondary cracking characteristics of pyrolysis oil, and rheological properties, we have established a more comprehensive physicochemical model for in-situ pyrolysis conversion of oil shale. This model can accurately predict phenomena observed in laboratory-scale and reservoir-scale experiments of oil shale pyrolysis, providing theoretical support for enhancing reservoir heating and oil-gas recovery. Accordingly, we propose a method of oil shale in-situ reverse pyrolysis by self-generated heat. This approach not only avoids the reservoir clogging issues faced by current technologies but also improves the stability of in-situ reactions and extraction rates. It increases oil recovery by over 10% and enhances energy efficiency by over 60% compared to existing technologies. The research findings provide critical theoretical and technical support for the efficient development of deep oil shale resources worldwide.
How to cite: Liu, Z.: Advancing Oil Shale In-Situ Pyrolysis: Accurate Multiphysics Prediction and Enhanced Extraction Method, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8608, https://doi.org/10.5194/egusphere-egu26-8608, 2026.
Lined rock cavern (LRC) offer a promising solution for underground hydrogen storage, which requires high pressure (>200 bar) to ensure economic viability due to hydrogen’s low volumetric density. In LRCs, the liner acts solely as a gas seal, while the rock mass bears the structural load. However, at economically feasible shallow depths (< few hundred meters), the high storage pressure significantly exceeds the low in-situ stress (on the order of 10 bars), creating a critical containment challenge.
Achieving safe containment under such a pressure difference requires accurate assessment of the mechanical strength of the rock mass. A criterion often used is to limit the load below the level when plastic deformation occurs. In many cases, however, this criterion still yields safe gas pressure which are below the desired level. Increasing gas pressure above this level means that some degree of plastic deformation will occur in the rock mass. This can take the forms of continuous deformation, jointing, or cracking.
Our knowledge from rock deformation experiments and LRC pilot sites indicates that there exists a safe level of inelastic deformation before storage integrity is compromised. However, the critical challenge lies in identifying how such inelastic deformation initiates, evolves, and redistributes under high internal pressure, as well as its implications for long-term cavern stability. Consequently, the mechanical response of the surrounding rock under high internal pressure remains a key uncertainty in stability assessment. Simplified elastic rheological models, which are commonly used in engineering design, may mask irreversible deformation processes in the near-field region of the cavern. In this study, a visco-elastic–viscoplastic (VEVP) model is employed to systematically investigate the mechanical behavior of the surrounding rock under cyclic gas pressurization, with particular focus on the role of rock plasticity. Model predictions are quantitatively compared with those obtained from a purely elastic formulation by varying the rock cohesion parameter. Under baseline conditions, the maximum radial displacement predicted by the VEVP model is 53% higher than that predicted by the elastic model, while the maximum circumferential strain increases by 186%. With the development of plasticity, the spatial distributions of strain and displacement evolve significantly. During the elastic stage, maximum circumferential strain is aligned with the principal stress directions, whereas maximum radial displacement occurs along directions oriented at 45° to the axes. As plastic deformation develops, the dominant deformation zone migrates toward the axial directions where plastic flow becomes most pronounced. Furthermore, plasticity-driven stress redistribution leads to stress relaxation and homogenization of deviatoric stress, accompanied by directional migration of pressure-dominated zones. Finally, the VEVP model elucidates a mechanical mechanism for potential lining–rock debonding caused by modulus mismatch. Upon depressurization, the steel lining undergoes nearly complete elastic rebound, while the surrounding rock retains irreversible plastic deformation, leading to asynchronous recovery and possible interface opening. These findings highlight the necessity of accounting for rock plasticity when assessing the mechanical stability and design of lined rock caverns for underground hydrogen storage.
How to cite: Wang, Y., Kiss, D., Wang, L. H., Yarushina, V. M., and Tajčmanová, L.: Influence of host-rock plasticity on deformation, stability, and liner detachment in pressurized lined rock caverns , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9386, https://doi.org/10.5194/egusphere-egu26-9386, 2026.
The response of tight rock to harness geothermal energy in unconventional systems involves highly coupled processes. Deep fluid circulation induces thermo-hydro-mechanical coupled processes that may lead to induced seismicity. The traditional concept for harnessing unconventional geothermal systems consists in hydro-shearing pre-existing fractures to enhance permeability thanks to dilatancy. Such concept, known as enhanced geothermal systems (EGS), has been deployed over a few decades, inducing earthquakes on several occasions, giving rise to project cancellation in some instances, like Basel (Switzerland) and Pohang (Korea Republic). Induced seismicity may be controlled by using a favorable stimulation protocol (Tangirala et al., 2024). However, coupled processes acting across the stimulated fracture network may eventually lead to induced earthquakes regardless of the stimulation protocol (Kivi et al., 2024). To minimize the risk of induced seismicity, closed-loop geothermal systems have been proposed because no fluid is injected into fractured rock, reducing the risk of fracture instability. However, since the circulating fluid along the closed loop is heated up just by conduction, a rapid thermal decline occurs along the lateral (in a multilateral setup). Even drilling tens of horizontal multilaterals at depth to decrease the flow rate circulating in each tube cannot effectively limit thermal decline at the outlet, making closed-loop geothermal systems inefficient for scalable electricity generation (Tangirala and Vilarrasa, 2025). Another alternative is multi-stage stimulation of EGS and, in particular, hydraulic fracturing-based EGS. In this concept, rather than hydro-shearing pre-existing fractures, hydraulic fractures connecting a doublet are created, limiting the risk of reactivating a large patch of a pre-existing fracture or fault. Yet, early thermal breakthrough may occur because of positive feedback mechanisms if a fracture starts attracting more water than the others because cooling opens up fractures, enhancing its transmissivity and attracting even more water. We provide a detailed assessment of the coupled processes occurring in these three unconventional geothermal systems and discuss their potential and limitations.
REFERENCES
Kivi, I. R., Vilarrasa, V., Kim, K. I., Yoo, H., and Min, K. B. (2024). On the role of poroelastic stressing and pore pressure diffusion in discrete fracture and fault system in triggering post-injection seismicity in enhanced geothermal systems. International Journal of Rock Mechanics and Mining Sciences, 175, 105673.
Tangirala, S. K., and Vilarrasa, V. (2025). On the limitations of closed-loop geothermal systems for electricity generation outside high-geothermal gradient fields. Communications Engineering, 4(1), 116.
Tangirala, S. K., Parisio, F., Vaezi, I., and Vilarrasa, V. (2024). Effectiveness of injection protocols for hydraulic stimulation in enhanced geothermal systems. Geothermics, 120, 103018.
How to cite: Vilarrasa, V., Tangirala, S. K., and Kivi, I. R.: Coupled thermo-hydro-mechanical processes and induced seismicity in unconventional geothermal systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9553, https://doi.org/10.5194/egusphere-egu26-9553, 2026.
New technologies have been developed to accomplish the Sustainable Development Goals, where Geoenergy is key for the transition. In recent years, some studies have suggested that changes in underground conditions could have a secondary impact on the local environment, for example in Carbon Capture and Sequestration leakage of CO2 can impact the health of surrounding vegetation; on Lithium Mining, fluctuations in the water level may affect the health or dynamics of the vegetation.
We propose a scalable Earth-observation-based framework for the spatio-temporal analysis of vegetation dynamics over time. Combining multi-sensor satellite data: Landsat constellation and Sentinel-2 imagery. We complemented these results with meteorological data from ECMWF Reanalysis v5 (ERA5); and in-situ water level datasets. The proposed approach integrates ecological interpretation with methodological robustness, enabling the systematic assessment of vegetation presence, persistence, and variability over time. We performed a validation analysis using PlanetScope imagery and in-situ meteorological data.
The workflow combines NDVI, and phenological metrics to generate a spatio-temporal vegetation dynamic characterization. The resulting products are designed to be readily integrated with complementary datasets, such as meteorological records and water-level observations, enabling their incorporation into impact assessments and environmental decision-making process.
Salar de Atacama (SdA), one of the world’s largest salt flats used for lithium production, hosts a variety of wetlands that are exposed to both extreme climatic conditions and increasing anthropogenic pressures. Understanding vegetation variability in this context is crucial for establishing robust environmental baselines and supporting long-term monitoring strategies.
Two areas of the salt flat have been selected to perform the analysis: i) surrounding area to Laguna Tebenquiche in the northern area (LTB); and ii) Vegas de Silao and Palolao on the South-East Border (SEB).
Both sites showed the peak NDVI season between late August to early November. Rainfall is concentrated between January and March, with high-magnitude events, confirming the dependence of vegetation on the availability of underground water.
By contrast, temperature exhibits a smooth, symmetric seasonal cycle, suggesting that thermal variability is secondary compared to hydrological pulses, but it should be considered in the snow melting process in the higher part of the basin.
The relative stability of LTB stations suggests shallow groundwater access, stable geomorphological settings, or vegetation assemblages adapted to predictable seasonal forcing. In contrast, the strong interannual variability observed at SEB indicates the vegetation activation is governed by episodic moisture availability.
NDVI peaks lag water-level increases, indicating a delayed vegetation response consistent with subsurface water availability rather than direct rainfall forcing. This lag is visible across sensors and persists across multiple years, reinforcing its ecological significance.
Water-level dynamics in the study area are influenced by multiple interacting processes, including lithium brine extraction rates, aquifer recharge from the upper basin, and direct recharge from rainfall. This study only evaluates the relevance of the methodology for vegetation assessment; it does not estimate the contribution of brine extraction to water levels.
The proposed methodology, when applied to SdA, demonstrates that the methodology effectively captures spatial and temporal patterns of vegetation response in a geoenergy context.
How to cite: Olea-Encina, P., Monserrat, O., Ramlie, M. C., and Crosetto, M.: Effects on vegetation due to geo-energy technologies, an Earth Observation approach: Salar de Atacama study case, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9618, https://doi.org/10.5194/egusphere-egu26-9618, 2026.
The in-situ conversion of oil shale has become an inevitable trend for exploitation due to the environmental friendliness and adaptability of deeper reservoirs. In-situ pyrolysis process actually occurred in a semi-closed system, in which kerogen cracking and hydrocarbon migration are inevitably affected by pressure. Additionally, pyrolysis zones far from the injection well remain below 400 °C, leading to prolonged heating stage. The atmospheric pressure rapid pyrolysis of oil shale is dissimilar from in-situ mining conditions. In light of this, this study comprehensively investigated the effects of pressure, temperature, and heating time on the pyrolysis behavior, yield and composition of pyrolysis products. For the effect of pressure, the shale oil yield of 8 MPa at 500 °C declined by 65.7 %, while the gas yield increased by 93.7 % when compared to atmospheric pressure. The pressure promoted the generation of light components and accelerated the conversion of alkenes to alkanes and aromatics in shale oil. The release temperature of gases increased under pressure, encouraging the production of alkane gas while reducing the hydrogen yield. Finally, the pyrolysis mechanism for oil shale coupling of temperature and pressure was proposed. Besides, with the extension of holding time, the maximum shale oil yield reached 65.90 %, 80.81 %, and 83.03 % of the Fischer oil yield at 350 °C, 380 °C, and 400 °C, respectively. Temperature and time exhibited a compensatory effect, with a distinct boundary observed between 350 °C and 380 °C for shale oil production. GC-MS analysis revealed that the proportion of medium- and short-chain alkanes in shale oil exceeded 75 %, while longer time enhanced the release of long-chain alkanes and exacerbated aromatization. Additionally, the accumulation of bitumen could enhance the heat capacity of semi-coke with an appropriate insulation at 350-380 °C, although it did not reverse the deterioration of combustion performance. An alternate pyrolysis pathway of organic matter based on bitumen transformation was proposed during the medium-temperature, long-duration in-situ pyrolysis process.
How to cite: Zhang, X., Guo, W., and Deng, S.: In-situ pyrolysis of oil shale in pressured semi-closed system: Insights into products characteristics and pyrolysis mechanism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9774, https://doi.org/10.5194/egusphere-egu26-9774, 2026.
Helium, like hydrogen, are critical resources essential to the energy transition. Despite different end uses for helium (e.g., coolant for fission and fusion reactors) and hydrogen (e.g., energy – storage, fuel), the two gases share key similarities, while also having some notable differences. It has been established that they have overlapping source mechanisms (e.g., radioactive decay within basement rocks, radiolysis associated with shales, etc.) resulting in the two gases being co-located in a number of exploration wells globally. Likewise, due to a similarity in the kinetic diameters of the molecules although not the reactive nature of them, physical traps that work for hydrogen, should in principle also work for helium. However, transport and trapping of these molecules are affected by a number of competing factors. Therefore, the transport mechanisms and rates at both a basin and pore-scale remain poorly understood.
Here we explore the nature of helium and hydrogen transport within porous media utilizing a microfluidic cell, representative of typical upper-crustal siliciclastics found in the subsurface, in combination with time-lapsed geometrical image analysis. At the pore scale, concentration of both elements (i.e. He, H2) within the pore space are dependent on a number of factors, including (1) the number of ejection pulses from a given source migrating through the same pore space, (2) the rate of arrival from the source, and (3) the impact of local hydrological currents on the pore space.
The laboratory experiments are combined with numerical modeling of multiphase fluid flow in porous media using a continuum approach. These models allow pore-scale observations from the microfluidic experiments to be upscaled, providing insight into the influence of flow rate, injection cyclicity, and permeability heterogeneity on gas migration and plume stability at the reservoir scale.
How to cite: Johnson, J., Kiss, D., Johnson, D., van Noort, R., and Yarushina, V.: Analogue modeling of non-reactive gas transport through porous media utilizing a microfluidic cell, in the context of He/H2 migration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10853, https://doi.org/10.5194/egusphere-egu26-10853, 2026.
Achieving climate neutrality by 2050, a target set by the EU, requires significant scale-up of CO2 storage. One economically attractive option is CO2 storage clusters where multiple operators inject CO2 into the same aquifer that may reach hundreds of kilometers in size. Injecting CO2 from multiple locations in the same aquifer introduces challenges, such as pressure interactions, even in the far-field beyond the storage project. Pressure build-up caused by neighboring fields could result in induced seismicity, potentially opening pathways in the fault damage zone (FDZ) within the caprock through which CO2 could escape. Such risks must be identified early to avoid injecting CO2 into problematic areas within a storage region.
For early-stage screening of high-risk locations, reduced-complexity methods, such as vertical equilibrium models, are suitable since the computational demand of detailed reservoir simulations is prohibitively high. However, currently these models do not account for the effect of pressure change on flow behaviour through the FDZ and the risk of fault reactivation since few constitutive relations exist, limiting their ability to reliably screen risks.
Developing such relations requires a detailed, project-scale understanding of key parameters controlling the risk of fault reactivation and flow behaviour through the FDZ, which includes multiscale fractures, ranging from grains to the thickness of the caprock. Those fractures cause stress perturbations, leading to heterogeneous permeability evolution that needs to be accounted for in models to reliably quantify upscaled flow properties under stress, as well as the risk of fault reactivation, in a realistic yet computationally feasible way.
We investigate the hydromechanical behaviour of the main fault and surrounding FDZ, using project-scale, sequentially-coupled simulations that include up to thousands of multiscale, planar fractures, following observations of realistic FDZ architectures. Stress, shear- and normal-displacement relationships for single mudrock fractures, derived from experimental data, are used to model intrinsic fracture permeability evolution and resultant upscaled FDZ permeability, while a semi-analytical method is employed to simulate aseismic shear slip on the main, planar fault surrounded by the FDZ, during the nucleation phase, and therefore to assess the risk of fault reactivation. The classical crack tensor theory is used for elastic geomechanical simulations, while the embedded discrete fracture model (EDFM) is employed for single-phase fluid flow simulations.
Preliminary results indicate significant stress perturbations, particularly in regions with higher fracture density (i.e., close to the fault core), which enhanced upscaled FDZ permeability under realistic stress boundary conditions. Initial simulations suggest that stress boundary conditions, and orientation and frictional properties of fractures and the main fault play an important role in controlling the magnitude of pore pressure increase required for fault reactivation and significant increase in upscaled FDZ permeability. Work is ongoing concerning systematic sensitivity analyses, with the aim of identifying key parameters controlling flow behaviour and the risk of fault reactivation. The results are expected to inform the development of constitutive relations required for screening of the risks in reduced-complexity models.
How to cite: Shinohara, T., Doster, F., Hajibeygi, H., and Geiger, S.: Coupled hydromechanical modelling of fault zones in clay-rich rock: towards management of fault-related risks in gigatonne-scale CO2 storage, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11990, https://doi.org/10.5194/egusphere-egu26-11990, 2026.
Three-dimensional ground-motion products help interpret deformation sources and support decisions in deforming regions. GNSS provides high-precision 3D displacement at station locations. InSAR adds dense spatial coverage, but it measures motion mainly along the satellite line of sight (LOS) and has lower temporal resolution and higher latency. We combine GNSS with EGMS InSAR time series to obtain consistent 3D surface deformation over Groningen (the Netherlands), where decades of gas production have produced subsidence.
GNSS PPP daily positions from Nevada Geodetic Laboratory are cleaned for network-wide common-mode signals, corrected for long-period trends, and then expressed in a local reference frame tied to a central station. EGMS “Basic” InSAR time series are updated using smooth calibration behavior derived from the corresponding “Calibrated” products. We align the InSAR and GNSS references by removing the mean LOS deformation near the reference GNSS antenna at matched epochs. For the integration, we pair GNSS stations with nearby persistent scatterers and synchronize the time series. The datasets are fused with an uncertainty-aware least-squares approach to estimate 3D displacement in the East–North–Up (ENU) frame. In this work, we explore spatio-temporal extensions, such as Kalman filtering, and multi-geometry InSAR integration (ascending and descending orbits) to improve continuity and reduce directional bias. Spatially continuous deformation products are generated from the fused 3D estimates using interpolation techniques.
The outcome is a set of 3D deformation time series and maps that merge the spatial coverage of EGMS with the full-component information provided by GNSS. In Groningen, the integration reduces LOS-driven ambiguity, producing 3D deformation products that are easier to interpret across sensors. The workflow is designed as a practical monitoring deliverable and a reproducible basis for site-specific analysis. These outputs can serve as monitoring deliverables and as observational constraints to support site-specific interpretation of coupled reservoir-deformation models used in geo-energy settings.
How to cite: Aponte, O., Gatti, A., and Realini, E.: Integrating EGMS InSAR and GNSS for 3D Surface Deformation Monitoring: Reservoir-Driven Ground Motion in Groningen, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12803, https://doi.org/10.5194/egusphere-egu26-12803, 2026.
Multiple clean energy sources are being adopted to collectively support the energy transition and decarbonization efforts. Legacy coal mines in shallow subsurface layers are potential heat geobatteries that can be repurposed to capture and store waste heat from nearby sources (e.g., supercomputing clusters and large-scale data centres). This stored heat can partially meet the heating needs of local residential and business units during winter months.
Repeated cycles of hot water injection and extraction in the coal mines cause thermo–hydro–mechanical (THM) changes, resulting in subsurface rock strains that are transferred to the ground surface as uplift/subsidence (deformation). Identifying magnitudes, patterns and key variables influencing surface deformation requires building representative coupled THM models.
Galleries to Calories (G2C) is a pilot project testing the geobattery concept in the Scottish legacy mines of the Midlothian Coalfield, southeast of Edinburgh. The subsurface is characterized by thin coal seams hosted within heterogeneous layered strata, posing challenges for reliable coupled THM models to predict deformation.
A fully coupled THM model was initially built using COMSOL Multiphysics and OpenGeoSys for basic model setup assessment and results comparison. The final model was validated using historical ground surface uplift data resulting from water rebound in the coal seams driven by regional groundwater flow. The validated model was then used to quantify and predict surface deformation caused by seasonal heat injection and extraction. The key variables influencing surface deformation were identified and ranked based on sensitivity analyses that accounted for parametric, structural, and regional groundwater flow uncertainties.
The study outcomes provide guidelines for defining technical design and operational constraints that ensure system stability and limit surface deformation, thereby reducing risks to existing buildings and infrastructure above the project area.
How to cite: Sidahmed, A. and McDermott, C.: Coupled THM Modeling to Predict Surface Deformation in Legacy Coal Mine Heat Geobatteries, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14056, https://doi.org/10.5194/egusphere-egu26-14056, 2026.
Temperature distribution in the geological subsurface of sedimentary basins is controlled by conductive and advective heat transport processes. The efficiency of these mechanisms is largely governed by the petrophysical properties of the rocks present in a sedimentary basin, with thermal conductivity being of primary importance for conductive heat transfer and permeability for advective heat transport. Sedimentary rocks exhibit a stratification-related anisotropy of both thermal conductivity and permeability, which plays a crucial role in the numerical assessment of thermal conditions in sedimentary basins.
In this study, numerical 3D simulations are carried out using the Thuringian Basin in central Germany as a case study to investigate the influence of anisotropic thermal conductivity and permeability of its Permo-Triassic sedimentary infill on the regional temperature distribution. The modeled results are compared with available temperature measurements in drill holes to evaluate the predictive capability of the simulations. In addition, sensitivity analyses are performed to validate and contextualize the results by quantifying the significance of anisotropic parameters relative to other controlling factors.
The simulation results indicate that accounting for the directional dependence of thermal conductivity and permeability has a significant impact on the regional temperature distribution. In particular, permeability anisotropy exerts a strong control on both the spatial position and the lateral extent of thermal anomalies. Models employing isotropic parameters may significantly underestimate the influence of stratification-induced anisotropy on the subsurface temperature distribution.
How to cite: Schulz, A. and Kukowski, N.: Influence of anisotropic rock properties on the regional temperature distribution in the Thuringian Basin, central Germany: A numerical simulation study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17480, https://doi.org/10.5194/egusphere-egu26-17480, 2026.
The island of La Palma, in the Canary Archipelago, hosts one of the most promising geothermal prospects in the Atlantic Ocean, linked to the active volcanic complex of Cumbre Vieja. The western sector of this edifice, encompassing the L1 geothermal anomaly, exhibits a high-enthalpy system previously inferred from the integrated data of geophysical surveys and geothermometry. This study presents a preliminary assessment of the electric power generation potential of the L1 reservoir in pre-exploratory conditions, integrating multidisciplinary data sets including 3D magnetotelluric inversion, ambient noise tomography and attenuation tomography, geodetic modelling, and multicomponent solute geothermometry.
A conceptual model of the L1 geothermal system was established and implemented in a 3D thermo-hydraulic simulation using the TOUGH2 code to evaluate the performance of a single-flash power plant supported by 21 deep wells (14 production and 7 reinjection). The geometry of the geological formations was constructed using GeoModeller, integrating available lithological data, stratigraphic information from water gallery excavations, and structural interpretations based on geophysical surveys. The model simulated multiphase flow and heat transport in porous and fractured volcanic media associated with the L1 anomaly. The simulations were implemented using the EOS1 equation of state, which accounts for water and steam as the only active phases, using variable density to enable convection. The simulations reproduced the natural steady-state conditions, used as input for the exploitation simulations. Uncertain reservoir and operational variables such as physical and hydraulic parameters of the reservoir and surface geological units were accounted and constrained through Monte Carlo stochastic simulations (100 realisations) over a 90-year production period. The simulations yielded expected net electric power outputs ranging from 23 to 45 MWe, with a median value of approximately 36 MWe, a P90 conservative estimate of 31 MWe, and a P10 optimistic scenario of 42 MWe.
The results highlight a stable, convective reservoir with temperatures of 213–231 °C at depths of 2.4–2.7 km, capable of sustaining long-term energy extraction with minimal thermal decline. These findings indicate that the L1 system represents a viable medium-to-high-enthalpy resource comparable to other productive basaltic geothermal fields worldwide. The development of this resource could significantly advance renewable energy transition in La Palma, reducing dependence on fossil fuels and contributing to the pathway toward carbon neutrality.
How to cite: Jiménez Beltrán, J., Baquedano, C., Martínez-León, J., Sariago, R., and García-Gil, A.: Thermo-hydraulic 3D modelling, multicomponent geothermometry and stochastic simulations integrated to assess geothermal potential and uncertainty in volcanic environments: insights from La Palma (Canary Islands), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18363, https://doi.org/10.5194/egusphere-egu26-18363, 2026.
The Illinois Basin–Decatur Project represents a landmark in Carbon Capture and Storage, with approximately 1 million tonnes of supercritical CO2 being injected into the Mt. Simon Sandstone. Nearly 20,000 microseismic events were recorded during injection, offering a unique opportunity to analyze the reservoir's geomechanical state. In this study, we use two datasets containing high-quality focal mechanisms to characterize the in-situ stress field and evaluate fault reactivation potential. We first apply a full stress inversion algorithm based on the Wallace-Bott hypothesis and stochastic optimization, constrained by vertical stress (Sv) and instantaneous shut-in pressure. The study area is dominated by strike-slip faulting regime (SHmax>Sv>Shmin), initial results assuming a fault friction coefficient of 0.6 and zero cohesion yield minimum activation pressure between 23.3 and 26.0 MPa. These values notably exceed the average downhole injection pressure of ~23.0 MPa, implying that, under the assumptions, the observed seismicity should not have been triggered. However, our refined analyses show that reducing the friction coefficient to 0.4 lowers the activation pressure to values 16.7–21.9 MPa. Alternatively, a comparable consistency can also be achieved by assuming lower values of shut-in pressure. Building on these results, we extend the analysis to systematically identify the optimal combination of SHmax magnitude and fault friction coefficient required to induce slip. We employ slip tendency analysis with nodal plane selection to ensure physical consistency. Using Shmin and Sv estimates derived from published stress gradients and density logs, we analyze the stability of the linked faults. We then perform a sensitivity-based search to identify the optimal range of friction coefficient and SHmax required to trigger fault slip. By varying SHmax and observing corresponding changes in the maximum mobilized friction coefficient, we narrow the potential stress magnitude range. For example, assuming an initial friction coefficient range of 0.45 to 0.6, the SHmax is constrained to approximately 74–92 MPa. Our results highlight that fault friction, while remaining poorly constrained at the site scale, represents a first-order control on induced seismicity and stress interpretation. Integrating high-quality source mechanisms with sensitivity-based constraints on stress magnitudes and fault properties is essential for the reliable forecasting and long-term risk assessment of large-scale geological CO2 storage.
How to cite: Guo, T., Wu, H., Eisner, L., Jechumtalova, Z., and Vilarrasa, V.: Optimizing stress tensors and friction coefficient from stress inversion of microseismicity at the Decatur CO2 storage site, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12961, https://doi.org/10.5194/egusphere-egu26-12961, 2026.
