• Review of over 60 deep geothermal case studies related or not to induced seismicity. • Seismic hazard is very low for mass-balanced circulation in porous aquifers. • Fractured and high-temperature reservoirs show moderate-to-high seismic hazard. • Brittle fractured igneous or sedimentary rocks are more prone to felt seismicity. • Seismic hazard assessment based on reservoir properties and operational conditions. This study reviews over 60 deep geothermal case studies to investigate the occurrence or absence of felt induced seismicity, across different reservoir types and exploitation strategies. The review highlights key patterns in seismogenic potential based on reservoir characteristics and operational methods. The potential for felt seismicity is very low for mass-balanced circulations in porous aquifers, low-to-moderate in deeper faulted or karstified sedimentary formations, while it is moderate-to-high for stimulations or circulations in fractured reservoirs and for production and reinjection operations in high-temperature geothermal fields. The presence of pre-existing faults or fractures, in a critical stress state and favorably oriented in the local stress field, constitutes an aggravating factor with respect to the seismic hazard of geothermal operations. The review further reveals that induced seismicity is poorly controlled by depth and lithology of the target formation but rather linked to rock competence and fractures characteristics. Higher seismic hazard is associated with brittle, low-porosity sedimentary or igneous rocks and with operations involving high-pressure stimulations or significant thermal and volumetric perturbations. The review confirms that the largest magnitude events often occur during the shut-in phase, highlighting that this trend is not only observed after reservoir stimulations but also after injection and circulation operations. These results emphasize that induced seismicity is governed by a complex interplay of geological, mechanical, and operational factors. The findings support the development of a framework for seismic hazard assessment tailored to geothermal reservoir characteristics and injection strategies, essential for mitigating risks in current and future geothermal projects.

Reactive transport modelling of CO2-enriched condensate reinjection in andesitic geothermal reservoirs towards the enhancement of carbon mineralisation

• Geothermal reservoirs of the Western Bohemian Massif are low-enthalpy (< 100 °C). • Reservoirs occur in crystalline basement at ∼2–4 km depth. • Thermal water circulation is focused along deep permeable fault systems. • Hydraulic connectivity exerts important controls on thermal water composition. The fault-bound basement-hosted geothermal systems of the Western Bohemian Massif (Germany) remain poorly constrained in terms of reservoir temperatures, circulation depths and recharge. Here, we present some of the first systematic constraints on these parameters based on a geochemical survey of regional thermal water, non-thermal groundwater and surface water, combining isotope techniques, a multi-method geothermometric approach and mixing calculations. Stable isotope ratios (δ 18 O and δ 2 H) indicate that all studied thermal waters are derived from meteoric precipitation. The geothermal reservoirs of the region are identified as low-enthalpy “hot water type” systems with temperatures generally < 100 °C. The occurrence of local warm springs is linked to radiogenic heating in primarily granitic reservoirs at depth and migration of thermal water to the surface along long-lived permeable fault systems. Despite having interacted with similar reservoir lithologies at comparable temperatures, thermal waters exhibit pronounced hydrochemical variability in terms of composition, mineralization and extent of water-rock interaction. These differences primarily reflect structural characteristics of the individual geothermal systems, such as hydraulic openness and fault connectivity, which in turn affect recharge rates, residence times, extent of dilution with non-thermal groundwater and the supply of dissolved CO 2 . Together, these results demonstrate that hydraulic connectivity and permeable fault architecture exert a first-order control on geochemical signatures in the geothermal systems of the Western Bohemian Massif and similar basement-hosted settings.

Heat extraction performance of horizontal wellbores under fracture-seepage coupling in deep geothermal reservoirs

Optimization reinjection strategies in a sandstone geothermal reservoir: Insights from laboratory experiments

Integrated Geothermal Reservoir Modeling with Geological Uncertainty and Well Placement Optimization

Vapor-dominated geothermal systems provide a reliable, low-carbon source of heat and electricity, but optimizing their exploitation requires high-resolution imaging of fracture networks and fluid pathways at the reservoir scale. We analyze a dense microseismic cluster in the northwestern Geysers (California), selecting 1,276 induced earthquakes recorded between 2006 and 2015. Using inter-event interferometry and fast-marching surface-wave tomography, we retrieve Rayleigh wave phase velocities on horizontal layers at 100m spacing and jointly invert them with previously derived local group velocities to obtain a quasi-3D shear-wave (Vs) model at ~ 100 × 100 × 10m blocks. The resulting Vs models reveal three main types of low-velocity anomalies: (I) fault-related zones associated with fracturing and hydrothermal alteration, (II) shallow steam-cap and normal-temperature-reservoir (NTR) boundary transitions spanning depths of ~ 900-1400m, exhibiting sharp Vs contrasts due to thermal and fluid effects, and (III) injection/engineering-related anomalies characterized by localized or vertically elongated low Vs patches. Integrating these results with induced microseismicity provides valuable insights into fracture activity, fluid migration, and stress evolution within the geothermal reservoir.

Reliable seismic characterization of geothermal reservoirs requires quantifying the effects of temperature on rock elastic properties. We investigate temperature-dependent seismic velocity evolution in shale through integrated laboratory ultrasonic measurements and finite-element modeling. The P- and S-wave velocities were measured on shale samples from China and the United States with diverse mineralogies over a temperature range from 20 °C to 200 °C, with numerical simulations extending the predictions to 300 °C. Results show a systematic decrease in P-wave velocity with increasing temperature. In contrast, S-wave velocity exhibits enhanced sensitivity to thermally induced micro-fracturing and pore-structure evolution, displaying a biphasic temperature response associated with the competing effects of thermoelastic softening and progressive microcrack development. Temperature-dependent rock-physics models incorporating evolving elastic moduli accurately reproduce the observed velocity trends. These findings establish a quantitative thermo-mechanical framework for interpreting seismic responses in shale-dominated geothermal systems and improve the reliability of seismic monitoring under high-temperature conditions.

Long term simulation of thermal solute transport in enhanced geothermal system reservoirs driven by fractal characterization of fracture morphology and experimental permeability parameters

Long-term hydrothermal evolution and sustainable operation of a deep carbonate geothermal reservoir: A field-calibrated 3D framework for the lower Friulian Plain, Italy

From subsurface data to heat economics: A novel machine-learning seismic workflow for geothermal reservoir delineation, subsurface derisking, and 3D modelling of deep triassic carbonates

Hydraulic fracturing has been prevailingly applied to induce thermal shock in geothermal reservoirs for the utilization of geothermal energy. With natural joints commonly distribute in the reservoirs, the stimulation mechanism of thermal shock on joint system is inevitably investigated at fracturing initiation stage to enlarge heat transfer space. In this paper, the interaction of hydraulic fractures (HFs) and joints was simulated by lattice-spring method (LSM). The factors of fluid viscosities, shock times, approaching angles, and joint sets were analyzed to reveal the stimulation effect of thermal shock. The results present that orthogonal approaching angle, moderate shock times, and low fluid viscosity are beneficial to the creation of heat transfer space. The radius of expansion region of the thermal shock is around 1 m, in which the interaction behavior of HFs mainly consists of arrest and penetration. This research aims at revealing the stimulation mechanism of thermal shock on joints and therefore improving the treatment of hydraulic fracturing in geothermal energy development.

Abstract Multi-perforation fracturing, despite its proven efficiency in unconventional oil and gas formations, remains rarely assessed for geothermal reservoir applications. Here, we systematically compared simultaneous fracturing (SMF) and sequential fracturing (SQF) using our newly established two-dimensional thermo-hydro-mechanical-damage (THMD) coupled numerical platform, quantifying fluid partitioning among multi-perforations and thermal stress effects. The analysis focused on fracture propagation behavior and multi-physical field evolution under varying dimensionless perforation spacings (DPS), defined as the ratio of perforation spacing to perforation length. Results revealed that SMF creates external fractures deviating 9–18° from the maximum principal direction, and the internal fracture requires higher initiation pressures and receives less fluid. In SQF, subsequent fractures deflect toward previous ones at DPS 3.3 but propagate along straight paths at DPS 6.7 and 10, with initiation pressures progressively increasing due to cumulative stress shadowing. Regarding multi-physical field evolution, the minimum principal stress transitions from compression to tension within fractures and near fracture tips. The internal fracture in SMF and subsequent fractures in SQF both exhibit higher pore pressure and lower temperature. Thermal stress primarily facilitates fracture development by reducing initiation pressure by approximately 5–8 MPa under the present conditions, while fluid pressure dominates fracture propagation. These findings provide fundamental insights for fracture network optimization and geothermal reservoir stimulation.

The formation and exploitation of geothermal reservoirs in hot dry rock (HDR) primarily rely on microseismic methods, but seismic techniques lack sufficient sensitivity to fluids. The electromagnetic method, however, demonstrates sensitivity to fluid movements during the monitoring of fracturing processes that form geothermal reservoirs in HDR. This study examines the role of electromagnetic methods in HDR development, taking China’s first Enhanced Geothermal System (EGS) demonstration site in the Qinghai Gonghe Basin as a case study. Based on the Gonghe HDR development site, a frequency-domain 3D borehole-to-surface electromagnetic forward modeling method with unstructured-grid discretization was employed to simulate the complex electromagnetic field responses induced by fracturing fluid injection and dynamic changes in fractures during HDR reservoir development. To enhance computational efficiency, a supercomputer was employed to perform 3D borehole-to-surface electromagnetic data inversion under conditions of massive multi-source and multi-frequency data. This quantitatively revealed the electrical characteristics at different depth intervals within the study area. The research demonstrates the feasibility of borehole-to-surface electromagnetic methods for determining the spatial distribution of fracturing injection, dynamically monitoring fracture development, and tracking fluid migration, thereby providing crucial technical support for monitoring HDR resources development.

Enhanced geothermal systems (EGS) is an environmentally friendly technology to effectively extract geothermal energy from hot dry rock (HDR). The fracture geometry of EGS is crucial for the utilization of geothermal reservoirs. This paper proposed a multiple stage fracturing wells (MSFW) EGS and evaluated its geothermal energy extraction performance by three-dimensional thermal-hydraulic-mechanic (THM) coupled numerical modeling. The MSFW EGS increases heat exchange area, and thus enhances heat extraction. The temperature and flow fields in MSFW EGS are compared with the multiple fracturing horizontal wells (MFHW) EGS, showing a higher temperature and power outputs. The effect of fracturing parameters (including fracture spacing, number of fractures, fracture width, fracture permeability and distribution) on heat extraction was investigated. The MSFW significantly improves the efficiency of EGS thermal extraction, thus opening up new perspectives for geothermal energy utilization.

Shear wear effect on cross-fracture: coupled seepage and heat transfer evolution and prediction of unstable slip risk in geothermal reservoirs

A study on cave compensation mechanism in heat extraction of fractured karst geothermal reservoirs

• The analytical model for the interpretation of a Harmonic Pulse Test (HPT) in naturally fractured geothermal reservoirs is derived. • The radial composite effect due to the thermal front is also considered. • Differently from Pressure Transient Analysis, neither a preliminary well closure nor the closure of neighbor wells is required. • Synthetic validation is provided against established analytical and numerical models. • The HPT is suitable for thermal front monitoring during ongoing operations in naturally fractured geothermal reservoirs. Well testing and conventional Pressure Transient Analysis (PTA) are fundamental and well-established methodologies for characterizing well and reservoir parameters. However, the applicability of PTA is limited during production or injection operations, since it requires a shut-in of the tested well, and it is significantly affected by interferences from neighboring wells. In previous works, we proposed, implemented, and validated against real data a methodology called Harmonic Pulse Testing (HPT). HPT is complementary to PTA. By specifically deploying the periodicity of rate and pressure signals, it has been designed to be applied during ongoing field operations. In this work, we present a new analytical solution for HPT in naturally fractured reservoirs. The proposed solution is also applied to geothermal systems, as it is coupled with a radial composite model capable of approximating the thermal front. The model has been validated against well-established analytical and numerical models under different scenarios. The calculation steps for converting the numerical dual-porosity model into storativity ratio and inter-porosity flow coefficient are also provided. The results of a validation exercise demonstrate that our model is robust against potential interference from other wells and allows the detection of the thermal front. The methodology can therefore be successfully applied during ongoing operations in naturally fractured geothermal reservoirs.

Robust optimization of fully coupled geothermal reservoir and power plant system based on deep learning

Qapqal Xibe Autonomous County is located in the central Yili Basin of Xinjiang. It possesses significant potential for geothermal resource development, but the lack of in-depth research on deep geothermal genetic mechanisms and refined resource evaluation restricts its large-scale utilization. Therefore, this paper integrates regional geological surveys, borehole thermometry, geophysical exploration, and hydrochemical and isotopic tracing to reveal the formation mechanism of the geothermal field. Furthermore, it quantitatively evaluates the resource potential and analyzes uncertainties by combining the volumetric method, analytical method, and Monte Carlo simulations. The results indicate that the shallow geothermal gradient is 2.2 °C/100 m, while the deep gradient increases to 3.8 °C/100 m. The Gagestai Fault and its secondary faults serve as dominant channels for deep thermal fluid migration. The Cretaceous Donggou Formation and the Jurassic Badaowan Formation constitute a dual-layer high-quality reservoir, with measured reservoir temperatures of 42.50 °C and 91.25 °C, respectively. Isotopic and hydrochemical analyses infer that the geothermal water mainly originates from atmospheric precipitation and snowmelt in mountainous areas. After long-distance deep circulation, cation exchange, and heating by the basement heat source, the fluid upwells along the faults to accumulate, forming a typical layered confined fault-controlled geothermal system. Resource evaluation, verified by Monte Carlo simulations, demonstrates that the volumetric method exhibits higher robustness at the current exploration stage. The total recoverable heat in the study area is 8.19 × 1016 J, classifying it as a medium-sized geothermal field. Rational development of these resources could save approximately 2.75 × 106 tons of standard coal and reduce CO2 emissions by about 7.315 × 106 tons. This study provides key parameters and a scientific basis for geothermal resource development in the Yili Basin, holding significant practical value for promoting the clean energy industry in Xinjiang and achieving the “dual carbon” goals.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-026-50632-w.