Search

The deep geothermal anomalies of the Upper Rhine Graben have long been identified (Haas and Hoffmann, 1929). They are typically attached to oil exploitation (Pechelbronn, Landau) or deep geothermal energy (Cloetingh et al.,2010; Vidal and Genter, 2018). We focus here on the area surrounding of the city of Landau (Germany) where both energies are exploited, on one hand, on the north of the city for the oil field and on the other hand, on the south of the city for the geothermal energy. In 2012, geodetic monitoring in Northern Alsace, France has begun (Heimlich, 2016). SAR acquisitions of TerraSAR-X satellite have been scheduled for a Franco-German border area west of the Rhine including the region of Landau. Direct evidence of significant surface deformation was observed in early 2014 south of the city of Landau, where unexplained cracks appeared on the geothermal power plant area during the production phase.The present work focuses on the results of the PS-InSAR analysis using StaMPS that cover the main period of displacement (2013-2014). The geodetic observations are completed by levelling measurements. These in situ measurements solve phase jump problems due to the high rate of displacement. The results show the time and space evolution of the surface displacements. It evidences also the active geological structures of the area. We developed a hydro-mechanical modelling of the deformation which gives insights into the main origin of displacement at depth related to the deep wells of the geothermal site but also questions the impact of the oil exploitation. [ABSTRACT FROM AUTHOR]

Hydrothermal systems are characterized by multiphase processes, which are responsible for heat transfer and complex chemical reactions involving the surrounding rocks. In active hydrothermal systems, hosted in volcanic, metamorphic or sedimentary settings, the geochemical study of thermal waters is crucial to understanding the features of the geothermal reservoir. In the last decades, a growing number of works have focused on the study of thermal waters with the final aim of evaluating deep temperature of geothermal systems. Solute geothermometers represent one of the major tools for the exploration of the subsurface geothermal resource as well as to estimate deep water temperatures and rock-water equilibrium at deep conditions.In Giggenbach (1988), the thermal-water composition is used to classify groups of water and their origin, and to prove if water-rock equilibrium (i.e the equilibrium of a thermodynamically stable mineral phase with water) is attained (Giggenbach 1981). Under equilibrium conditions, water-rock interaction implies the simultaneous existence of dissolution, precipitation and exchange processes under given temperature, pressure and salinity conditions. If the equilibrium is attained, geo-thermometers can provide a realistic evaluation of the temperature. Alternatively, if the equilibrium is only partially attained or other processes are involved (e.g. seawater, cold brines, connate waters), interpretation of temperatures obtained from geothermometry equations requires to be critically evaluated in order to avoid over-interpretation of the analytical results. Details of methods and some application examples will be discussed. [ABSTRACT FROM AUTHOR]

Fluid injection in rocks is one of the standard ingredients of the underground reservoir development. Productions of shale hydrocarbons or geothermal energy as well as massive disposals of saltwater or carbon dioxide require broad applications of this technology. The fact that a fluid injection causes seismicity has been well-established for several decades. Understanding and monitoring of fluid-induced seismicity is necessary for hydraulic characterization of reservoirs, for assessments of reservoir stimulation and for controlling of the related seismic risk. One can show that a linear pore-pressure relaxation corresponding to distant domains of enhanced geothermal systems and a hydraulic fracturing of shale reservoirs are two asymptotic end members of a set of non-linear diffusional phenomena responsible for seismicity triggering. These are special cases of a rather general non-linear pressure diffusion equation taking into account a strong enhancement of the hydraulic diffusivity tensor. This equation can be considered as a wave equation corresponding to an anisotropic propagation of a non-linear poroelastic Biot slow wave. This formulation provides descriptions of forward- and backward fronts of propagating pressure perturbations. They correspond to the triggering and back fronts of induced seismicity. Also the spacial density of microseismic clouds can be described by this wave. Real induced-seismicity data confirm adequacy of this model. [ABSTRACT FROM AUTHOR]

The terrestrial heat flow is the only observable geophysical quantity that in principle can reflect the thermal effects of deep-seated geodynamic processes. On the other hand, this parameter is particularly difficult to measure. Most of the available heat flow information derives from thermal measurements in the uppermost layers of the crust and thus may include both transient components, related to the tectonic history, and geological noise. Especially in young and active deformation areas, processes such as basin formation and sedimentation, groundwater circulation and thrusting may drastically change the temperature distribution in the shallow crust and hide the deep conductive thermal regime of the lithosphere. Temperature and petrophysical data obtained in hydrocarbon and geothermal exploratory wells, as well as scientific drillings, may help to unravel the deep undisturbed thermal regime. However, temperature measurements must be treated with appropriate techniques to remove the thermal perturbation due to the drilling operations, and the thermophysical properties of rocks must be evaluated by taking into account the effects of the overburden pressure, temperature, anisotropy and fluids filling the pores. Moreover, the radiogenic heat production, which in shallow boreholes can be neglected, should be taken into account when processing data from several kilometres deep wells. In this paper, we analyse deep thermal data to unravel the lithosphere thermal regime in the central-northern Apennines chain and the surrounding sedimentary basins. Besides groundwater flow, the several kilometres thick sedimentary formations are still affected by thermo-tectonic perturbations (sedimentation and overthrusting), whereas the underlying crystalline basement should be in an undisturbed, conductive thermal regime. Unfortunately, few thermal data were recorded in the metamorphic basement and most of the available temperature values were measured in the permeable carbonate Palaeogene-Mesozoic formations, which represent the major and widespread tectono-stratigraphic unit of the study area. First, we corrected for the drilling disturbance the available temperatures from hydrocarbon and geothermal wells by means of a technique specifically calibrated for the Apennines foreland basins. Subsequently, we estimated the thermal conductivity profiles on the basis of detailed litho-stratigraphic information derived from deep wells and by taking into account the pressure and temperature effects. Finally, the thermal resistance approach, including also the effect of radiogenic heat production, was used to determine the terrestrial heat flow. In each well, an optimum surface heat-flow value was found by minimising the differences between the calculated and corrected temperatures. We noticed that only a few boreholes close to recharge areas show a mismatch between calculated and observed temperatures, thus arguing for deep groundwater flow in the permeable carbonate unit, whereas most of the obtained heat-flow data may reflect the deep thermal regime. [ABSTRACT FROM AUTHOR]

We show that near-realtime seismic monitoring of fluid injection allowed control of inducedearthquakes during the stimulation of a geothermal well near Helsinki, Finland. The injectionwell, OTN3, was drilled down to 6.1 km-depth into Precambrian crystalline rocks. WellOTN3 was deviated 45∘ from vertical and an open hole section at the bottom was divided intoseveral injection intervals. A total of 18,159 m3 of fresh water was pumped into crystallinerocks during 49 days in June- and July, 2018. The stimulation was monitored in near-realtime using (1) a 12-level seismometer array at 2.20-2.65 km depth in an observation welllocated 10 m from OTN3 and (2) a 12-station network installed in 0.3-1.15 km deepboreholes surrounding the project site. Earthquakes were processed within a fewminutes and results informed a Traffic Light System (TLS). Using near-realtimeinformation on induced-earthquake rates, lo-cations, magnitudes, and evolutionof seismic and hydraulic energy, pumping was either stopped or varied betweenwellhead-pressures of 60-90 MPa and flow rates of 400-800 l/min. This procedure avoidedthe nucleation of a project-stopping red alert at magnitude M2.1 induced earthquake, alimit set by the TLS and local authorities. The stimulation resulted in detection of>43,000 earthquakes with -1.2<ML<1.9. The original catalog was relocated usingdouble-difference technique to improve hypocenter precision. The 4032 relocatedearthquakes were used to investigate the spatio-temporal evolution of seismicity, seismicenergy release, and maximum magnitude in response to injection. We found hypocenterdistribution, Gutenberg-Richter (GR) distribution and relation between hydraulic andradiated energy suggest (re-)activation of size limited network of distributed fractures.The temporal behavior of G-R b-value, as well as a lack of temporal (Omori-type)correlations in a presence of spatial localization of earthquakes suggest very limitedearthquake triggering and stress transfer at low level of ambient stress. The maximumobserved magnitudes scale with stored elastic (=hydraulic) energy, following afracture-mechanics based model of Galis et al. (2017). Our results suggest a possiblephysics-based approach to controlling stimu-lation induced seismicity in geothermalprojects. [ABSTRACT FROM AUTHOR]

The purpose of this research is to evaluate the potential of geothermal resources and heat flow characteristics as well as scheme of Enhanced Geothermal System(EGS) and Complex Energy Extraction from Geothermal resource, (CEEG) in Zhi-Ben area, Taiwan. A three-dimensional conceptual model has been developed based on the site information including lithological character, hydrogeological data, etc. Then the simulator, TOUGH2, has been carried out to construct a comprehensive hydrothermal model of the study area. In this research, we firstly assess groundwater potential zone of Zhi-Ben river watershed integrating with lithology, land cover/land use, drainage, slope and lineaments. The field investigations and collections of data including surface geological survey, geo-structure, geophysical methods (self- potential, nature radio-activities, electrical resistivity tomography), geochemical data, groundwater level and temperature of wells as well as geothermal gradient are performed to establish hydrogeological conceptual model. The model can be used to describe the groundwater characteristics in Zhi-Ben area. Furthermore, the model accompanying with TOUGH2 will use to evaluate the potential of geothermal resources and observe heat flow behaviors of heat reservoir under the consideration that the geothermal potential zone is defined. Finally, the sensitive analysis of heat production of geothermal wells in terms of geological variables of potential zone will be calculated by numerical model TOUGH2 in EGS and CEEG, respectively. Computational results indicate that the geothermal energy produced from abandoned wells depends largely on the geothermal gradient. The research can be the reference in development in management of geothermal areas. [ABSTRACT FROM AUTHOR]

Volcanic islands commonly testify the strict relation between volcano-tectonic activity and slope instability as very recently testified by the flank collapse of the Anak Krakatau active volcano which induced the destructive tsunami on 23 December 2018. The island of Ischia (Italy), which is part of the Phlegrean Volcanic District, has experienced since the Holocene several slope scale instabilities (i.e. debris- and rock avalanches). The latter occurred as direct consequence or feedback of a rapid caldera resurgence and associated seismicity and/or renewal of hydrothermal and magmatic systems. An ongoing slope-scale gravitational deformation process still affects large volumes of a thick greenish alkali-trachytic tuff sequence (the Mt. Epomeo Green Tuff - MEGT -) cropping out on the western flank of Mt. Epomeo (Mt. Nuovo), that represents the remnant of the caldera's most uplifted sector. The rock mass affected by ongoing deformation mobilized along a structurally controlled biplanar compound shear zone.In order to assess the relations and the possible interactions between the ongoing gravitational deformation and the hydrothermal system beneath the island, thermal and thermo-mechanical models of deep geothermal and slope systems were respectively reconstructed. Based on available geomechanical and petrophysical characterization under relevant temperature and pressure conditions, as well as on literature wells' geothermal profiles, a 2D thermo-mechanical model of the Mt. Nuovo slope was designed. A numerical model was computed along a section crossing the Mt. Nuovo slope, where ongoing deformation is testified by geomorphic evidence. The model was validated adopting an uncoupled thermal and mechanical numerical solution, back-analyzing the ongoing slope-scale gravitational process.The outcomes highlight the main role of Mass Rock Creep (MRC) in the onset of the slope instability, suggesting the interactions with the geothermal field in modifying the stress-strain response of the slope, which is able to alter its short- and long-term gravitational equilibrium.Thermo-baric field induced by hydrothermal rejuvenation can interact with the slope equilibrium causing the mechanical weakening of the compactant (i.e. ductile) MEGT tuff as consequence of transient exposure to high thermal perturbations, therefore increasing the rate of slope deformation. The thermo-mechanical numerical models, once constrained by geomorphic evidence and monitoring data, can be adopted for defining future scenarios (i.e. forward modelling) resulting by variation of physical conditions and/or mechanical parameters of the rock masses involved in the gravity-induced slope deformations. Through these forward analyses is possible to depict the worst physical conditions leading to ultimate paroxysmal events consisting in a generalised and catastrophic slope failure. [ABSTRACT FROM AUTHOR]

Obtaining qualitative information about the stress state in the Earth's crust is a challenging task. Typically, direct measurements of crustal stresses are not included in logging programs of geothermal wells, especially while drilling in high enthalpy reservoirs in which temperature conditions often exceed operational limits of the conventional logging equipment. There are a number of methods for assessing stress state of the reservoir, all of which adhered to the petroleum industry, and include sonic logging, hydraulic fracturing, leak-off tests, borehole breakouts analysis and stress indications from core samples studies. Unfortunately, only in a few geothermal wells, these methods are being applied. This is often due to either high investment costs, challenges during core recovery or extremely high reservoir temperatures. Obtaining reliable estimates of parameters such as minimum and maximum horizontal, vertical stresses and pore pressure is vital for ensuring safe drilling operations and increasing the learning curve for the future drilling operations. This study proposes a method for the assessment of crustal stresses using non-direct stress measurements such as circulation losses, multi-arm mechanical caliper logs, and analysis of continuously measured drilling parameters. A MATLAB-based software for assessing minimum and maximum horizontal stresses and breakout orientation from multi-arm mechanical caliper recordings was developed. The proposed methods do not require additional equipment or costs and can be simply extracted from already recorded parameters during drilling. The analysis carried out in this study was based on the results from deep drilling in the Los Humeros Geothermal Field, the third largest field in Mexico, located at the border of Veracruz and Puebla states in the central-eastern part of the country, where the highest recorded temperature recorded was 395°C and hostile reservoir fluids were produced. Throughout almost 40 years of drilling operations in the field, issues related to wellbore instability have been observed. Such complications might be prevented or mitigated in future operations once solid knowledge about reservoir geomechanics is assessed prior to the drilling activity. Additionally, this study proposes an approach for computing the base data needed for the geomechanical modeling on the example of the central part of the Los Humeros Geothermal Field. [ABSTRACT FROM AUTHOR]

Although geothermal energy has shown to be a low pollution energy source; air, soils and water next to geothermal plants may be affected by their operation. One of the largest geothermal energy source of the world, "Cerro Prieto" with a capacity of 720 MW, is located northwest Mexico within an agricultural area. The abstracted geothermal fluids enriched in As, B, Pb, Cd, and other heavy metals, are either reinjected to the aquifer or send to an evaporation pond located in the geothermal plant. However, since spills have occurred at other geothermal zones, it is important to evaluate the effect of those contaminants on soils of the surrounding area and their possible infiltration to shallow groundwaters. To that aim, soils (one chromic vertisol and two calcic regosols) from three sites close to the Cerro Prieto plant were sampled to evaluate their behavior regarding As, Pb and B retention. Batch experiments were carried out using the soils as the sorbent and geothermal water from three geothermal wells as the sorbate. Raw water concentrations were: As 0.2442 mg/L, 0.2774 mg/L and 0.738 mg/L, B 18.409 mg/L, 13.5075 mg/L and 16.646 mg/L, Pb 0.27mg/L, 0.16mg/L and 0.3 mg/L. Physico-chemical characteristics of the soils were determined and related to the experimental results. A good adjustment of the chromic vertisol sample to Freundlich isotherms was observed for As (r2>0.9), followed by Pb (r2=0.61), and B (r2>0.5); besides, As retention also showed a good adjustment to the Langmuir model (r2>0.9). The retention followed the order Pb>As>>B in one of the two calcic regosols, while the other only retained Pb>>As. Cationic exchange capacity, and clay minerals, carbonate, organic matter, Fe, Al and Mn amorphous and crystalline oxides contents influenced the soils retention capacity. Irrigation with the geothermal water would not imply a toxicity risk to plants raised in the chromic regosol due to its high Pb and As sorption capacity. Lead concentration would not be a toxicity problem in one of the calcic regosols for the same reason but As and boron would be more available. Boron would be a hazard to vegetables and water due to its low or lack of retention in the three soils, and also for its possible infiltration to shallow groundwater that is used for irrigation in the area. This study highlights the importance of maintaining a good and controlled operation of the geothermal plant. [ABSTRACT FROM AUTHOR]

In order to determine suitable locations for geothermal exploration, reliable predictions of theearth’s subsurface temperature field are essential. For these predictions, it is necessary toconsider the uncertainties of the involved parameters. However, with the currentstate-of-the-art simulations standard uncertainty quantification methods, such as MarkovChain Monte Carlo are computationally intractable for basin-scale models at high resolution.We thus require numerical methods that considerably accelerate the forward simulation toenable the use of uncertainty quantification approaches that can easily require up to a millionforward simulations. For this purpose, we introduce the reduced basis method, a physics-based machinelearning approach. Our previous studies show that we obtain speed-ups of four to six ordersof magnitude in comparison to standard finite element simulations. One main advantage of the reduced basis method in contrast to other surrogate modelsis that we obtain temperature values at every point in the model and not only atthe observation points. Consequently, we can generate uncertainty maps of thetemperatures at the target depth of the geothermal wells for the entire extent of thebasin. We use the Brandenburg (Germany) model to illustrate the application and benefits of thereduced basis method for large-scale geological models. The numerical simulations arerealized within the DwarfElephant package, an open-source high-performance applicationbased on the Multiphysics Object Oriented Simulation Environment (MOOSE)developed by the Idaho National Laboratory. The DwarfElephant package offers aphysics-independent and user-friendly access to the reduced basis method within ahigh-performance finite element library, allowing computations of spatially highdimensional models. In addition, we present how the method can be used for other inverseprocesses, such as automated model calibrations. Inverse problems are becoming rapidlyextremely expensive computationally even without including all major sources ofuncertainty. In that regard, the reduced basis method is very promising because it allows asignificant reduction in computation time without introducing additional physicaluncertainties. [ABSTRACT FROM AUTHOR]