Geothermal energy is a green source of power that could play an important role in climate‐conscious energy portfolios; enhanced geothermal systems (EGS) have the potential to scale up exploitation of thermal resources. During hydraulic fracturing, fluids injected under high‐pressure cause the rock mass to fail, stimulating fractures that improve fluid connectivity. However, this increase of pore fluid pressure can also reactivate pre‐existing fault systems, potentially inducing earthquakes of significant size. Induced earthquakes are a significant concern for EGS operations. In some cases, ground shaking nuisance, building damages, or injuries have spurred the early termination of projects (e.g., Basel, Pohang). On the other hand, EGS operations at Soultz‐sous‐Forêts (France), Helsinki (Finland), Blue Mountain (Nevada, USA), and Utah FORGE (USA) have adequately managed induced earthquake risks. The success of an EGS operation depends on economical reservoir enhancements, while maintaining acceptable seismic risk levels. This requires state‐of‐the‐art seismic risk management. This article reviews domains of seismology, earthquake engineering, risk management, and communication. We then synthesize “good practice” recommendations for evaluating, mitigating, and communicating the risk of induced seismicity. We advocate for a modular approach. Recommendations are provided for key technical aspects including (a) a seismic risk management framework, (b) seismic risk pre‐screening, (c) comprehensive seismic hazard and risk evaluation, (d) traffic light protocol designs, (e) seismic monitoring implementation, and (f) step‐by‐step communication plans. Our recommendations adhere to regulatory best practices, to ensure their general applicability. Our guidelines provide a template for effective earthquake risk management and future research directions.

The fundamental objective of earthquake engineering is to protect lives and livelihoods through the reduction of seismic risk. Directly or indirectly, this generally requires quantification of the risk, for which quantification of the seismic hazard is required as a basic input. Over the last several decades, the practice of seismic hazard analysis has evolved enormously, firstly with the introduction of a rational framework for handling the apparent randomness in earthquake processes, which also enabled risk assessments to consider both the severity and likelihood of earthquake effects. The next major evolutionary step was the identification of epistemic uncertainties related to incomplete knowledge, and the formulation of frameworks for both their quantification and their incorporation into hazard assessments. Despite these advances in the practice of seismic hazard analysis, it is not uncommon for the acceptance of seismic hazard estimates to be hindered by invalid comparisons, resistance to new information that challenges prevailing views, and attachment to previous estimates of the hazard. The challenge of achieving impartial acceptance of seismic hazard and risk estimates becomes even more acute in the case of earthquakes attributed to human activities. A more rational evaluation of seismic hazard and risk due to induced earthquakes may be facilitated by adopting, with appropriate adaptations, the advances in risk quantification and risk mitigation developed for natural seismicity. While such practices may provide an impartial starting point for decision making regarding risk mitigation measures, the most promising avenue to achieve broad societal acceptance of the risks associated with induced earthquakes is through effective regulation, which needs to be transparent, independent, and informed by risk considerations based on both sound seismological science and reliable earthquake engineering.

Abstract Two closely spaced geothermal doublets were operated in the Californië geothermal field near Venlo, the Netherlands. The geothermal wells target the Dinantian Zeeland formation below 2 km depth. For several years, hot fluid was produced from the Tegelen fault, a regional fault in the Roer Valley rift system, until a felt M1.7 earthquake led to the suspension of geothermal activities. The Californië showcase provides a rare opportunity to retrospectively evaluate the assessment and the management of induced seismicity risks for a geothermal project. A seismic hazard assessment was conducted at several stages of the project, and seismicity was continuously monitored with a local station network. In this paper, we report on the characteristics of the induced seismicity and evaluate the findings of the seismic hazard assessments conducted prior to the earthquakes. Seismic hazard assessments were based on numerical simulations of subsurface stress changes associated with geothermal operations. A geomechanical analysis indicated that the mapped faults in the subsurface are likely to be critically stressed. The largest hazard was inferred to result from thermo-elastic stresses, originating from cold water injection close to the Tegelen fault. Subsequent earthquakes predominantly occurred near a production well after stopping or reducing production. We attributed this observation to a thermo-elastic stress load caused by cold water injection close to the Tegelen fault, combined with a counter-acting stabilisation of the fault due to pressure depletion during production. This mechanism was consistent with the dominating mechanism considered in the preceeding seismic hazard assessments. Although geothermal operations have not resumed yet, the geomechanical analysis indicates that re-locating one of the injection wells further away from the Tegelen fault could provide an efficient measure for mitigating induced seismicity risks at Californië.

Injection-induced seismicity represents a major challenge for the development of Enhanced Geothermal Systems (EGS). To effectively mitigate the associated seismic hazard, a better understanding of the spatiotemporal evolution of induced seismicity and its efficient modeling are required. Towards that end, a stochastic framework within the continuous time random walk (CTRW) theory is used to make inferences regarding the diffusion properties of injection-induced seismicity in three cases of hydraulic stimulations in EGS. The analysis of seismicity within the CTRW context indicates multi-scaling variations in the waiting times distributions and in the evolution of the mean squared distance of seismicity with time, both associated with the co- and post-injection periods, respectively. During fluid-injections, an almost Poissonian waiting times distribution is followed by broad distributions during post-injection, enhancing long-term clustering effects and inter-earthquake interactions. At the same time, the rate of triggered earthquake diffusion drastically drops during the post-injection period for all the studied cases. Such properties may have implications on the main driving mechanisms of injection-induced seismicity in EGS, highlighting the transition from a dominant pressure-driven triggering mechanism during fluid-injections, to a mixed mechanism after termination of injections, where stress transfer effects and inter-earthquake interactions become more important.

The global energy landscape is currently experiencing a significant shift towards non-hydrocarbon, sustainable energy sources, often referred to as 'green energy'. This transition is being driven by the urgent need to address the problem of global warming caused by greenhouse gases, most of which are generated by the burning of fossil fuels. This article provides an overview of the role that subsurface geomechanics will play in this transition, focusing on green energy technologies such as carbon sequestration, geothermal energy production, hydrogen storage and nuclear waste disposal. The article starts with a review of geomechanical properties and structures that will be relevant to the green energy transition, such as <i>in situ</i> stresses, elastic moduli, strength properties, permeability, faults and fractures. This is followed by introductions to the four green energy technologies mentioned above. The next section focuses on the specific geomechanical challenges associated with each of these technologies, such as surface subsidence, induced seismicity and fluid and contaminant leakage. Gaps in existing knowledge, and potential pitfalls to be avoided, are highlighted. The article concludes with a brief discussion of public perception of environmental risks associated with subsurface energy technologies. It is concluded that geomechanics will play a key role in each of these emerging subsurface energy technologies, and the knowledge and tools that have mainly been developed in the context of fossil fuel exploitation will be key to these developments.

ABSTRACT Fracture caging limits hydraulic fracture growth and the activation of faults during high-rate high-pressure fluid injection using pre-drilled boundary wells around the injection well. If successful, this approach could offer a means to limit injection induced seismic magnitudes by preventing the activation of large faults outside of the cage. This concept has many possible applications, but the most relevant should be geothermal energy where caging could enable safe and economic energy production. In this study we explore the validity of caging using experiments and models to identify the well design, flow rate, economic, and engineering limits for deploying caging successfully in the field. Our work shows that the two primary mechanisms for failure of a cage can be attributed to poor well-fracture connectivity due to poor well placement in uncertain stress fields or due to undersized production wells. Ultimately, we find that (1) fracture caging combined with (2) limited entry injection wells, (3) high-temperature directional drilling, and (4) sustained high-pressure high-rate injection could unlock vast reserves of geothermal energy, all without requiring major new technological advancements. INTRODUCTION The concept of fracture caging was initially focused on containing the growth of hydraulic fractures by placing boundary wells around an injection well prior to high-pressure high-rate hydraulic stimulation (Frash et al., 2018). In addition, it appears to be poss

Enhanced geothermal systems (EGSs) expand geothermal energy production in reservoirs with low natural permeability by inducing fractures or exploiting existing fracture networks to improve permeability and fluid circulation. In this context, fault-damage zones (FDZs) are particularly relevant because they control fracture connectivity, govern localized permeability enhancement, and act as critical pathways for fluid migration and stress redistribution. These zones strongly influence the mechanical and hydraulic properties of the reservoir rock mass, thereby affecting stimulation efficiency and long-term system performance. Accurate characterization of these zones is thus necessary for a successful stimulation to avoid unresponsive/disconnected areas or trigger seismic activity. In this study, we focus on OPTV data collected at 11 boreholes strategically positioned to intersect the major fault-damage zones at the Grimsel Test Site (GTS), Switzerland. The OPTV datasets include significant artifacts generated by drilling operations and previous hydraulic stimulation experiments, which must be filtered to isolate the natural fracture network. While structural geology studies have long recognized complex damage-zone architectures (e.g., Kim et al., 2004 ), such architectural detail is not always incorporated into reservoir-scale models. In several site-specific reservoir modeling studies, damage zones have been represented as simplified planar discontinuities without explicit reso

The power to run the heat pump comes from another source. Geothermal energy escapes as hot water at many hot springs or as steam at geysers. In the United States, most geothermal reservoirs of hot water are in the western states, Alaska, and Hawaii. Wells can be drilled into underground reservoirs for the generation of electricity. Some geothermal power plants use the steam from a reservoir to power a turbine / generator, while others use the hot water to boil a working fluid that vaporizes and then turns a turbine. Hot water near the surface of Earth can be used directly for heat. Direct-use applications include heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurizing milk. Hot dry rock resources occur at depths of 3 to 5 miles (5–8 km) everywhere beneath the Earth's surface and at lesser depths in certain areas. Access to these resources involves injecting cold water down one well, circulating it through hot fractured rocks, and drawing off the heated water from another well. Currently, nobody uses this method commercially.