The induced seismicity in the Groningen gas field, The Netherlands, presents contrasted spatio-temporal patterns between the central area and the south west area. Understanding the origin of this contrast requires a thorough assessment of two factors: (1) the stress development on the Groningen faults and (2) the frictional response of the faults to induced stresses. Both factors have large uncertainties that must be honoured and then reduced with the observational constraints. Ensembles of induced stress realizations are built by varying the Poisson's ratio in a poro-elastic model incorporating the 3-D complexities of the geometries of the Groningen gas reservoir and its faults, and the historical pore pressure distribution. The a priori uncertainties in the frictional response are mapped by varying the parameters of a seismicity model based on rate-and-state friction. The uncertainties of each component of this complex physics-based model are honoured through an efficient data assimilation algorithm. By assimilating the seismicity data with an Ensemble-Smoother, the prior uncertainties of each model parameter are effectively reduced, and the posterior seismicity rate predictions are consistent with the observations. Our integrated workflow allows us to disentangle the contributions of the main two factors controlling the induced seismicity at Groningen, induced stress development and fault frictional response. Posterior distributions of the model parameters of each modelling component are contrasted between the central and south west area at Groningen. We find that, even after honouring the spatial heterogeneity in stress development across the Groningen gas field, the spatial variability of the observed induced seismicity rate still requires spatial heterogeneity in the fault frictional response. This work is enabled by the unprecedented deployment of an Ensemble-Smoother combined with physics-based modelling over a complex case of reservoir induced seismicity.

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Surface deformation can be detected with satellite-based geodetic sensors, providing important insights on subsurface geomechanical properties. In this study, we use Interferometric Synthetic Aperture Radar (InSAR) observations to measure ground deformation due to fluid extraction and due to an induced seismic event at the Los Humeros Geothermal Field (Puebla, Mexico). The result of the PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) analysis shows that the subsidence at the LHGF was up to 8 mm/year between April 2003 - March 2007, which is small relative to the produced volume of 5x106 m3/year. The subsidence pattern indicates that the geothermal field is controlled by sealing faults separating the reservoir into several blocks. Our models imply small volume changes in the reservoir and the different nuclei of strain solutions differ only slightly. These findings suggest that the pressure within the reservoir is well supported and that reservoir recharge is taking place. The occurrence of induced seismicity is independent evidence for the development of effective stresses. The inversion of the coseismic deformation due to the 8 February 2016, Mw 4.2 earthquake showed activation of a shallow normal fault in a reverse manner. Even with the limited compaction observed from the subsidence, the stress development was enough to induce seismicity. Pore pressure contrasts over a fault will increase the stress development. However, the fault structure will be more complex than assumed in the present study, because an acceptable joint match of ascending and descending surface movement data was not possible. An integrated study into the complex reservoir behaviour and the associated stress development over complex faults is therefore warranted.@en

We investigate ground movements induced by the 8 February 2016, Mw=4.2 earthquake at the Los Humeros Geothermal Field (Mexico) using Sentinel-1 radar interferometry. Previous estimated focal mechanism solution based on seismic data with a hypocentral depth of 1900 m could not resolve the measured coseismic surface deformation pattern. In this study, we applied inverse elastic dislocation models to estimate the source parameters of the seismic event. Our models suggest the reverse reactivation of the Los Humeros normal fault at a shallower depth (<1000 m), with a more significant left lateral component below ~400 m depth. The occurrence of such shallow events at Los Humeros pose increased risks for the neighboring communities and infrastructure. Therefore, continuous monitoring of seismicity and cautious planning of field operations are crucial.

A NNW-SSE striking fault swarm, including the Los Humeros fault, acts as a major boundary of the subsiding area observed by InSAR time-series between February 2016 and May 2019. A potential explanation of the reverse reactivation of the Los Humeros fault and following downward movement of the eastern fault block is the depressurization of the whole hydrothermal system. Such depressurization can occur due to the exploitation of the geothermal field and/or due to natural pressure/temperature changes related to magmatic activity.@en

In February and March 2020 most European countries were confronted with the outbreak of the coronavirus disease 2019 (COVID-19). The Dutch Outbreak Management Team (OMT) and hospitals were in urgent need of forecasts that could help prepare for the increasing number of patients requiring ICU beds and that could also assess the effect of government measures to limit virus transmission. In the early stages of the outbreak, earth scientists from TNO and TU Delft both recognised the possibilities to apply Earth-science-based modelling expertise for these challenges. The two teams, working independently, both developed models to forecast the outbreak in different countries and to assess the effectiveness of social distancing measures@en

Surface deformation due to fluid extraction can be detected by satellite-based geodetic sensors, providing important insights on subsurface geomechanical properties. In this study, we use Differential Interferometric Synthetic Aperture Radar (DInSAR) observations to measure ground deformation due to fluid extraction at the Los Humeros Geothermal Field (Puebla, Mexico). Our main goal is to reveal the pressure distribution in the reservoir and to identify reservoir compartmentalization, which can be important aspects for optimizing the production of the field. The result of the PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) analysis shows that the subsidence at the LHGF was up to 8 mm/year between April 2003 and March 2007, which is small relative to the produced volume of 5×106 m3/year. The subsidence pattern indicates that the geothermal field is controlled by sealing faults separating the reservoir into several blocks. To assess if this is the case, we relate surface movements with volume changes in the reservoir through analytical solutions for different types of nuclei of strain. We constrain our models with the movements of the PS points as target observations. Our models imply small volume changes in the reservoir, and the different nuclei of strain solutions differ only slightly. These findings suggest that the pressure within the reservoir is well supported and that reservoir recharge is taking place.

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Within the Netherlands, 24 geothermal systems have been realized of which 16 are operational, together producing 3.4 PJ of heat in 2018 (status date 1-1-2019). The main application domain is horticulture. The ambition of the Dutch government is to see production of geothermal energy increase in the Netherlands to 50 PJ in 2030, subsequently 200 PJ in 2050 and also to expand the application domain to district heating and industry. A state of the art resource assessment can support the Dutch government policy to realize its ambition. By classifying the resources based on project maturity including reference to the obstructing issues in the maturation of projects such as technical, financing, licensing and or social and environmental complexities targeted policy can be drafted. As of January 2019, 51 exploration licenses have been granted, and 31 more have been applied for (MEA2019). At least one geothermal project is defined in each of these exploration licenses, at different levels of advancement. Outside the boundaries of existing licenses and licenses under application, the Netherlands provides ample space for geothermal development. At the moment, there are no tools or practical methodologies to integrate all available information in a coherent and automated manner. As such, a method to quantify the geothermal energy resources of projects ‘not yet realized’ using the United Nations Framework Classification (UNFC) resource classification system would help policymakers to decide upon the most appropriate measures to remove obstructions for reaching the 2030-2050 geothermal ambitions. In this study, we show the initial results of a resource assessment and classification system for geothermal energy while incorporating environmental and social issues in the classification, as required by the UNFC2009. As basis for this resource assessment, we use the web tool ThermoGIS-v2.1 (Vrijlandt et al. 2019). ThermoGIS-v2.1 using information on the Dutch subsurface derived from the regional mapping by the Geological Survey. It is updated through incorporation of newly gained insights and data and provides a comprehensive overview of the geothermal potential for a selected set of aquifers. The resource estimates, including the uncertainty range related to these figures, at the status date 1-1-2019 of the Dutch geothermal “project portfolio” are classified using UNFC, resulting in a set of resource figures per resource class according to project maturity: commercial, potentially commercial, non-commercial and exploration projects. @en

On the 8th of February 2016, a Mw 4.2 earthquake was detected inside the Los Humeros caldera, located in the eastern sector of the Trans-Mexican Volcanic Belt. The event occurred after a sharp increase in the injection rate at the Los Humeros Geothermal Field and it was recorded by the seismic monitoring network of the power plant. The earthquake was felt by the local population and it caused damage in the power plant infrastructure. The focal mechanism solution of a previous study based on seismological data shows a reverse movement with a minor left-lateral component: Mw=4.2, depth=1500m, strike=169°, dip=61°, rake=42°. We have performed a geodetic and geomechanical analysis of the seismic source event based on ground deformation inferred from DInSAR. We used ascending and descending Sentinel-1 differential interferograms to retrieve the horizontal and vertical components of the co-seismic deformation. Subsequently, we inverted the estimated deformation to obtain the solution of an activated fault using the Okada model. These results shed light on the geomechanical aspects of the event and can help to understand the effects of field operations interacting with pre-existing structural features and active tectonic processes in the Los Humeros caldera.@en

In this paper we present results of a global resource assessment for geothermal energy within deep aquifers for direct heat utilization. Greenhouse heating, spatial heating, and spatial cooling are considered in this assessment. We derive subsurface temperatures from geophysical data and apply a volumetric heat-in-place method to improve current global geothermal resource base estimates for direct heat applications. The amount of thermal energy stored within aquifers depends on the Earth's heat flow, aquifer volume, and thermal properties. We assess the thermal energy available by estimating subsurface temperatures up to a depth of three kilometer depending on aquifer thickness. The distribution of geothermal resources is displayed in a series of maps and the depth of the minimum production temperature is used as an indicator of performance and technical feasibility. Suitable aquifers underlay 16% of the Earth's land surface and store an estimated 4·10⁵ to 5·10⁶ EJ that could theoretically be used for direct heat applications. Even with a conservative recovery factor of 1% and an assumed lifetime of 30 years, the annual recoverable geothermal energy is in the same order as the world final energy consumption of 363.5 EJ yr⁻¹. Although the amount of geothermal energy stored in aquifers is vast, geothermal direct heat applications are currently underdeveloped with less than one thousandth of their technical potential used.

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We present first results of PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) time-series over the eastern sector of the Trans-Mexican Volcanic Belt including several volcanic systems. The study area covers the Los Humeros and Acoculco geothermal fields. Los Humeros is one of the largest geothermal fields in Mexico connected to a caldera system that has been active from 0.46 Ma until recent. We performed PS time series analysis using the StaMPS method on Sentinel-1 images acquired between October 2016 and December 2017 to resolve ongoing ground deformation. The Sentinel-1 satellite provides regular observations with fine temporal resolution over large areas, which facilitates detection of satellite line-of-sight surface movements important for monitoring geothermal exploration activities. Generally, the interferograms are of good quality with high coherence even on long time scales. Most of the study area is located at high altitudes (above 2000 m) with strong relief. Asa result, the interferograms seem to be influenced by topography-related atmospheric phase delays, identified by the high correlation between phase and elevation. We correct the topography-related atmospheric phase delays and compare the InSAR estimated displacements with the available GPS data. Our goal is to obtain the deformation associated with ongoing geothermal activities over the Los Humeros geothermal field and other tectonic processes that might be present in the area. Here we present our first results, which will be further extended to estimate volume changes related with the geothermal exploration by inversion methods.@en