ERE2.5

Geothermal energy is known as a renewable source that has little effect on environment, since no burning process is involved in the producing of thermal and electric energy. Geothermal water is considered an environmentally friendly energy source which is valuable especially in polluted areas. Our study area, the Baia Mare region, is located in the northwestern part of Romania, a region known as one of the most polluted environment in Romania due to its long-lasting local mining and metallurgical activities. Additional quantities of CO2 emissions resulted from the use of various, relatively cheap, heating sources by the local population. The main goals of our study are to evaluate the subsurface geothermal potential of the Baia Mare area and to identify promising geothermal exploitation sites. Heat flow values in this area are among the highest in Romania. We therefore plan to combine geological, geophysical, geochemical and hydrogeological data (geo-data) in order to provide a geoscientific solution for increasing the geothermal energy production in this part of Romania. Our research program contains surface geological mapping, geophysical surveys (active and passive seismic, magnetic, magnetotelluric and geothermal), geochemical analysis, hydrogeological surveys, modeling of geo-data and joint interpretation of geo-data. An initial 3D geothermal model will be built using existent geo-data. This model will help us to identify subsurface structures which show high potential for geothermal exploration. Interpretation of existent active seismic data collected during previous hydrocarbon exploration will provide information about the subsurface structural geology. The results of the new interpretation will be compared and correlated with the existent geological maps and sections for the study area. The magnetic data available in the public domain will be used to identify subsurface igneous bodies. The temperature data available from previous measurements will be used to build temperature-versus-depth distributions. These results will be analysed within a larger geodynamic framework. A pilot site will be selected after the analysis of the initial 3D geothermal model on which we plan to collect and record new geo-data. Data processing, inversion and modeling will be performed in order to create the final geothermal model with locations of promising exploitation wells. 

How to cite: Panea, I., Gaina, C., Mocanu, V., Munteanu, I., Petrescu, L., Matenco, L., Scradeanu, D., Tuluca, F., Scradeanu, M., Nache, F., Zlibut, A., Bouaru, C.-F., Minakov, A., and Magni, V.: A multidisciplinary study for geothermal energy sources identification in the Baia Mare area (Romania), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-549, https://doi.org/10.5194/egusphere-egu21-549, 2021.

In the fast-growing economies around the world, the demand for energy as well as environmental concerns make geothermal energy a potential renewable energy source. Most geothermal provinces across the world have the capacity to generate enormous amounts of hydrothermal energy, and hot springs in these areas are generally associated with active volcanic or tectonic activity. With modern technical advancement, low enthalpy geothermal systems (< 100°C) are also being considered for geothermal energy production. In non-volcanic hot springs, the water temperature remains low compared to volcanic hot springs. We study two such hot springs located within Neoproterozoic granulites of the tectonically stable Eastern Ghats Belt (EGB) of the Indian shield. The source of heat for these amagmatic hot springs may either be deep-seated fracture zones, or alternative heat sources at shallow crustal levels. A combination of geological, geochemical, hydrological and geophysical techniques has been applied to characterize non-volcanic hot springs in India. The hot springs at Atri and Tarbalo are located to the south of the Mahanadi Shear Zone within the EGB. Penetrative granulite facies planar structural fabrics in rocks of the northern EGB are reoriented within an E-W striking, northerly dipping ductile shear zone that is subsequently dissected by WNW-ESE trending, sub-vertical pseudotachylite-bearing faults and fractures. Tube and dug wells around the shear zone yield both hot (~ 60°C) and cold (~ 28°C) water, sometimes spatially only 20 metres apart. Chemical analyses indicate both have distinct compositions, with hot waters rich in Na⁺, K⁺ and Cl^- while cold-waters have higher Ca²⁺ and HCO₃^- concentration. Stable isotope analyses (δ²H and δ¹⁸O) of both waters indicate that both are meteoric in origin. Tritium (³H) and ¹⁴C analyses indicate that hot spring waters are much older than the non-thermal groundwater. The hot water is 17714 years old, while the non-thermal groundwater indicates modern day recharge. This suggests that both waters come from different reservoirs. VLF-electromagnetic studies indicate that water exists in isolated pockets beneath the crystalline country rocks, but also circulated through WNW-ESE trending fracture systems. Heat production studies reveal that the EGB is a high radiation zone, and some host rocks have exceptionally high heat producing element (HPE) concentrations (primarily thorium) within the minerals monazite and thorite. Hence, meteoric water is entrapped in those “perched aquifers” near HPE-rich pockets for a long duration and has sufficient time to undergo radiogenic heating, shielded from the non-thermal groundwater circulating within the fracture system. These isolated pockets act as sources for the hot springs,with HPE being the source of heat. The high HPE distribution in the crust resulting from Neoproterozoic geological events has, thus, elevated the present-day equilibrium geotherm in the EGB, forming sources for shallow-level, non-volcanic hot springs within a tectonically inactive terrane. Therefore, the hot springs in these regions, as well as the hot dry rocks of these areas can be considered as potential geothermal resources.

How to cite: Maitra, A., Gupta, S., Singh, A., and Kessari, T.: Geological, geochemical and geophysical studies on the non-volcanic hot springs, Atri and Tarbalo in the Indian shield: potential unconventional renewable energy sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2783, https://doi.org/10.5194/egusphere-egu21-2783, 2021.

Fluid, as an elemental component of a geothermal system, transports and distributes underground heat according to the topographic driving force within a groundwater basin. As the water table configuration has diverse and distinct forms in real-life basins, asymmetric hydraulic head variation may occur from basin to basin in accordance with real physiographic characteristics. Therefore, the effects of an asymmetric water table distribution in groundwater basins were investigated in several model sets with special emphasis on the temperature field and with the help of five response parameters: maximum temperature of outflowing water, average temperature, the portion of the thermal water reservoir, Péclet number and location and extent of thermal water discharge.

Our simulation results showed that in the absence of thermal springs, the extent of the thermal water reservoir might be larger and the temperatures might be higher. Sedimentary basin fill fosters the formation of heat accumulation under and within this unit. As a new “parameter” in the basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus it controls the location of basin parts bearing the highest geothermal potential. So if thermal water can reach the ground surface, the discharge might not take place exactly above the thermal water reservoir due to the asymmetric driving forces of groundwater flow. Furthermore, the extent and temperature of thermal water reservoirs are also influenced by local-scale anisotropy, heterogeneities, i.e. faults, fault zones and fractures, and, of course, basal heat flux.

Therefore, the application of asymmetric basin-scale models in preliminary geothermal potential assessment would be beneficial for understanding heat distribution. The results also have further implications on the identification of prospective areas and planning of shallow and deep geothermal energy utilization, the interplay between basin-parts and rejuvenation of geothermal resources.

This research is part of the ENeRAG project that has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 810980.

How to cite: Tóth, Á., Galsa, A., and Mádl-Szőnyi, J.: Regional groundwater flow conditions and preliminary geothermal potential in asymmetric basins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8657, https://doi.org/10.5194/egusphere-egu21-8657, 2021.

The geothermal hot water reservoir underlying the coastal township of Waiwera, northern Auckland Region, New Zealand, has been commercially utilized since 1863. The reservoir is complex in nature, as it is controlled by several coupled processes, namely flow, heat transfer and species transport. At the base of the aquifer, geothermal water of around 50°C enters. Meanwhile, freshwater percolates from the west and saltwater penetrates from the sea in the east. Understanding of the system’s dynamics is vital, as decades of unregulated, excessive abstraction resulted in the loss of previously artesian conditions. To protect the reservoir and secure the livelihoods of businesses, a Water Management Plan by The Auckland Regional Council was declared in the 1980s [1]. In attempts to describe the complex dynamics of the reservoir system with the goal of supplementing sustainable decision-making, studies in the past decades have brought forth several predictive models [2]. These models ranged from being purely data driven statistical [3] to fully coupled process simulations [1].

Our objective was to improve upon previous numerical models by introducing an updated geological model, in which the findings of a recently undertaken field campaign were integrated [4]. A static 2D Model was firstly reconstructed and verified to earlier multivariate regression model results. Furthermore, the model was expanded spatially into the third dimension. In difference to previous models, the influence of basic geologic structures and the sea water level onto the geothermal system are accounted for. Notably, the orientation of dipped horizontal layers as well as major regional faults are implemented from updated field data [4]. Additionally, the model now includes the regional topography extracted from a digital elevation model and further combined with the coastal bathymetry. Parameters relating to the hydrogeological properties of the strata along with the thermophysical properties of water with respect to depth were applied. Lastly, the catchment area and water balance of the study region are considered.

The simulation results provide new insights on the geothermal reservoir’s natural state. Numerical simulations considering coupled fluid flow as well as heat and species transport have been carried out using the in-house TRANSport Simulation Environment [5], which has been previously verified against different density-driven flow benchmarks [1]. The revised geological model improves the agreement between observations and simulations in view of the timely and spatial development of water level, temperature and species concentrations, and thus enables more reliable predictions required for water management planning.

[1] Kühn M., Stöfen H. (2005):
      Hydrogeology Journal, 13, 606–626,
      https://doi.org/10.1007/s10040-004-0377-6

[2] Kühn M., Altmannsberger C. (2016):
      Energy Procedia, 97, 403-410,
      https://doi.org/10.1016/j.egypro.2016.10.034

[3] Kühn M., Schöne T. (2017):
      Energy Procedia, 125, 571-579,
      https://doi.org/10.1016/j.egypro.2017.08.196

[4] Präg M., Becker I., Hilgers C., Walter T.R., Kühn M. (2020):
      Advances in Geosciences, 54, 165-171,
      https://doi.org/10.5194/adgeo-54-165-2020

[5] Kempka T. (2020):
      Adv. Geosci., 54, 67–77,
      https://doi.org/10.5194/adgeo-54-67-2020

How to cite: Grafe, A., Kempka, T., Schneider, M., and Kühn, M.: Revised hydrogeological model of the hydrothermal system Waiwera (New Zealand), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12196, https://doi.org/10.5194/egusphere-egu21-12196, 2021.

Drilling boreholes during exploration and development of geothermal reservoirs not only involves high cost, but also bears significant risks of failure. In geothermal reservoir engineering, techniques of optimal experimental design (OED) have the potential to improve the decision making process. Previous publications explained the formulation and implementation of this mathematical optimization problem and demonstrated its feasibility for finding borehole locations in two- and three-dimensional reservoir models that minimize the uncertainty of estimating hydraulic permeability of a model unit from temperature measurements. Subsequently, minimizing the uncertainty of the parameter estimation results in a more reliable parametrization of the reservoir simulation, improving the overall process in geothermal reservoir engineering.

Various OED techniques are implemented in the Environment for Combining Optimization and Simulation Software (EFCOSS). To address problems arising from geothermal modeling, this software framework links mathematical optimization software with SHEMAT-Suite, a geothermal simulation code for fluid flow and heat transport through porous media. This contribution shows how to determine experimental conditions such that the uncertainty when estimating different parameters of model units from temperature measurements in the borehole is minimized. Numerical simulations of synthetic geothermal reservoir scenarios are presented to demonstrate the OED workflow and its applicability to geothermal reservoir modeling

How to cite: Fink, J. and Seidler, R.: Predicting Optimal Borehole Locations for Parameter Estimation in Geothermal Reservoirs Using Optimal Experimental Design, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12419, https://doi.org/10.5194/egusphere-egu21-12419, 2021.

To the welfare of both economy and communities, our society widely exploits geo-resources. Nevertheless, with benefits come risks and even impacts. Understanding how a given project intrinsically bares such risks and impacts is of critical importance for both industry and society. In particular, it is fundamental to distinguish between the specific impacts related to exploiting a given energy resource and those shared with the exploitation of other energy resources. In order to do so, it is useful to differentiate impacts in two categories: routine impacts – caused by ordinary routine operations, investigated by Life-cycle assessment with a deterministic approach – and risk impacts – caused by incidents due to system failure or external events, investigated by risk assessments with a probabilistic approach. The latter category is extremely interesting because it includes low probability/high consequences events, which may not be completely independent or unrelated, causing the most disastrous and unexpected damages. For this reason, it is becoming more and more crucial to develop a strategy to assess not only the single risks but also their possible interaction and to harmonize the result obtained for different risk sources. Of particular interest for this purpose is the Multi-Hazard/Multi-Risk Assessment.

The aim of our work is to present an approach for a comprehensive analysis of impacts of geo-resource development projects. Routine operations as well as risks related to extreme events (as e.g.,seismic or meteorological) are linked using a Multi-Hazard Risk (MHR) approach built upon a Life-Cycle analysis (LCA). Given the complexity of the analysis, it is useful to adopt a multi-level approach: (a) an analysis of routine operations, (b) a qualitative identification of risk scenarios and (c) a quantitative multi-risk analysis performed adopting a bow-tie approach. In particular, after studying the two tools, i.e. LCA and MRA, we have implemented a protocol to interface them and to evaluate certain and potential impacts.

The performance of the proposed approach is illustrated on a virtual site (based on a real one) for geothermal energy production. As a result, we analyse the outcome of the LCA, identify risk-bearing elements and events, to finally obtain harmonised risk matrices for the case study. Such approach, on the one hand, can be used to assess both deterministic and stochastic impacts, on the other hand, can also open new perspective in harmonizing them. Using the LCA outputs as inputs of the MRA can allow the analyst to focus on particular risk pathways that could otherwise seem less relevant but can open new perspective in the risk/impact evaluation of single elements, as we show in this case study.

This work has been supported by S4CE ("Science for Clean Energy") project, funded from the European Union’s Horizon 2020 - R&I Framework Programme, under grant agreement No 764810 and by PRIN-MATISSE (20177EPPN2) project funded by Italian Ministry of Education and Research.

How to cite: Gargiulo, M. V., Garcia, A., Amoroso, O., and Capuano, P.: An integrated approach to assess both risk and impacts related with geo-resources exploration and exploitation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2216, https://doi.org/10.5194/egusphere-egu21-2216, 2021.

We investigated the relationship between the geothermal fluids and the fracture networks that control the storage and fluid pathways of geothermal systems in the northern part of the Malawi Rifted Zone (MRZ). The MRZ is a magma-poor rift located in the Western Branch, where potential geothermal energy is postulated from elevated heat flow and the emergence of hot springs through fracture zones. However, there is a lack of knowledge about the fracture networks that control fluid pathways and storage of the geothermal systems in the region.

Preliminary geothermometer calculation studies of hot springs in the MRZ suggested that the highest geothermal reservoir temperatures (200 °C) are found in the northern region. Additionally, the hot springs are associated with the local meteoric water that seeps through deep fracture zones. These structurally-controlled geothermal systems are characterized by geothermal fluids stored in fracture zones with vertical fluid rise (upflows) and/or in shallow sedimentary rocks with  horizontal geothermal circulation (outflows) deposited in basins along the MRZ. 

The guiding hypothesis is that interconnected regional joints, inherited reactivated structures, and Quaternary faults comprise a complex fracture network that controls the geothermal fluid transport and storage of geothermal systems in the northern part of the MRZ. Therefore, this study aims to quantify the relationship between complex fracture networks and geothermal fluids in this region. Here the term “complexity” means fracture networks that show a wider range of orientations and higher intensity than other areas. We use digital elevation models to map structures, density maps of fracture intensity, and topology characterization to identify surface level connectivity. Additionally, we use high-resolution aeromagnetic data to identify possible conductive structures at depth and the relationship between Precambrian structures and geothermal systems. 

The preliminary results show that most of the hot springs in the Karonga area are located in Permian-Triassic and Quaternary basins with ~NNW-SSE fault trends. Also, the hot springs are focused on a region of higher fracture intensity with a favorable setting related to terminations of ~NNW-SSE faults and intersections with reactivated Precambrian foliations (NW-SE). The Chiweta hot spring, the highest reservoir temperature in Malawi, is located at an intersection between NE-SW, N-S, and NW-SE fault systems. Aeromagnetic data shows that most of the hot springs are aligned with the deep conductive structures ~NW-SE oriented of the Karonga Fault Zone (KFZ). The KFZ has been associated with the reactivation of the Precambrian Mughese Shear Zone.

The expectations of this research are: 1) to provide a better understanding of the fracture networks that transport the geothermal fluids, 2) to identify permeable areas to mitigate the high-risk of drilling non-productive wells, and 4) the low-cost methodology used in this study can be applied in similar areas of the Western Branch.

How to cite: Davalos-Elizondo, E. and Lao Davila, D.: Assessment of the fracture networks controlling geothermal fluids in the northern part of the Malawi Rifted Zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-977, https://doi.org/10.5194/egusphere-egu21-977, 2021.

The geochemical characteristics of the Calabrian thermal waters have already been investigated in several studies which adopted a sort of ‘‘regional’’ approach.  On the other hand, the recent works by Vespasiano et al., 2014 and Apollaro et al. 2019 were focused to specific thermal sites with the aim to investigate the geochemistry and to reconstruct the local geothermal conceptual model. In this study, was adopted the same ‘‘local’’ approach to investigate the geochemistry of the warm and cold-water discharges from the Cotronei and Caccuri thermal area. Bruciarello, Cotronei (Ponte Coniglio) and Repole thermal areas fall in the proximity of the western side of the Crotone Basin made up of terrains structured between the middle Miocene and Holocene, transgressive on the crystalline basement belonging to the Sila massif. The Basin, located on the Ionian side of the PCO (Peloritan Calabrian Orogen), was interpreted like a forearc basin in the inner portion of the Calabrian accretion wedge.

Geochemical and hydrogeological data allow to identify the presence of (i) a deep primary geothermal endmember hosted into the crystalline basement (Cotronei system), and (ii) secondary shallow systems developed in the Miocene sedimentary successions (Bruciarello and Repole). All thermal waters have shown different composition: Na(Ca)-Cl composition for Ponte Coniglio-Cotronei (EC 3.57 ± 0.22 mS/cm), Na(Ca)-Cl(SO₄) composition for Bruciarello (EC 8.17 ± 0.76 mS/cm) and Na-SO₄(Cl) composition for Repole (EC 4.15 mS/cm). The water-rock interaction between primary fluids and evaporitic succession leads to the formation of the secondary Bruciarello and Repole systems. In these sites, the thermal endmember, hosted in the crystalline basement, infiltrates within Miocene evaporitic successions and undergone important compositional changes due to Anhydrite (or gypsum) and sodium Al-silicates dissolution (e.g. Albite) followed by precipitation of phases such as calcite and clay minerals (e.g. Caolinite).

The silica geothermometers indicated temperatures of 55 ± 2 °C for the endmember and slightly lower temperatures for the remaining two systems. Furthermore, δ¹⁸O and δ²H values highlight a meteoric origin for all thermal systems and provide infiltration altitude of about 1650 – 1850 m a.s.l. that agree with the Sila plateau heights.

Assuming a geothermal gradient of about 33°C/km, a temperature for the deep thermal reservoir of ⁓55 °C and an average atmospheric temperature of 6°C in the recharge area (Sila plateau), it can be assumed that the meteoric waters descend to depths of 1500 m, where the thermal aquifer is located. This data would confirm the location of the primary geothermal reservoir within the crystalline basement.

Apollaro C., Tripodi V., Vespasiano G., De Rosa R., Dotsika E., Fuoco I., Critelli S., Muto F. 2019. Chemical, isotopic and geotectonic relations of the warm and cold waters of the Galatro and Antonimina thermal areas, southern Calabria, Italy. Marine and Petroleum Geology. 109, 469–483. https://doi.org/10.1016/j.marpetgeo.2019.06.020

Vespasiano G., Apollaro C., Muto F., Dotsika E., De Rosa R., Marini L. 2014 - Chemical and isotopic characteristics of the warm and cold waters of the Luigiane Spa near Guardia Piemontese (Calabria, Italy) in a complex faulted geological framework. Applied Geochemistry, 41, 73-88.

How to cite: Vespasiano, G., Muto, F., De Rosa, R., Cipriani, M., Dotsika, E., and Apollaro, C.: Preliminary geochemical and isotopic characterization of the warm and cold waters of the Cotronei (Ponte Coniglio), Bruciarello and Repole thermal areas, (Calabria - Southern Italy)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8715, https://doi.org/10.5194/egusphere-egu21-8715, 2021.

Non-magmatic, orogenic geothermal systems are recognized as significant energy resources for electricity production or direct uses. This study focuses on the non-magmatic geothermal system hosted by the Agua Blanca fault, Ensenada, Mexico. The Agua Blanca fault is a 140 km long transtensional structure with segments recording up to 11 km of dextral strike-slip displacement and normal throws of up to 0.65 km. We have identified at least seven geothermal areas manifested by hot springs discharging at temperatures ranging from 38 °C to 107 °C. These systems involve topography-driven infiltration of meteoric water deep into the Agua Blanca fault and exfiltration of the heated water at valley floors and along a local beach known as La Jolla.

For this contribution, we present recent and ongoing exploration activities aiming to (i) obtain a fundamental understanding of the governing thermal-hydraulic-chemical processes controlling the circulation of meteoric water in the hydrothermally active fault system and (ii) quantify the natural discharge rate and its respective advective heat output. Chemical and isotopic analyses of thermal springs and seismic epicenters' location reveal that meteoric water penetrates between 5 to 10 km deep into the brittle orogenic crystalline basement and thereby attains temperatures between 105 and 215 °C. Interestingly, the deepest circulation and hottest reservoir temperatures occur where the extensional displacement along the fault shows maximum values. However, our data provide no evidence that meteoric water infiltrates beyond the brittle-ductile zone in the crust (12-18 km).

For the La Jolla beach thermal area, we have quantified the advective heat output from thermal images acquired with an unmanned aerial vehicle equipped with a thermal camera and from water flow and direct temperature measurements. The total thermal water discharge is 330 ± 44 L s^-1 and occurs over a surface area of 2804 m² at temperatures up to 52 °C. At 20 cm depth, the temperature is as high as 93 °C. These observations collectively imply a current heat output of 40.5 ± 5.2 MW_t (Carbajal-Martínez et al., 2020). We are currently estimating the shape and magnitude of the subsurface thermal anomaly at La Jolla beach by performing coupled thermal-hydraulic-chemical simulations using the code Toughreact.

We conclude that meteoric water circulation through the Agua Blanca fault system reflects the interplay between the permeability distribution along the fault system and the rugged regional topography. Under ideal conditions such as at La Jolla beach, such circulation generates rather large thermal outputs that could supply the thermal energy for a multi-effect distillation desalinization plant and contribute to cover the shortage of fresh water in Ensenada.

How to cite: Daniel, C.-M., Peiffer, L., Diamond, L. W., Fletcher, J. M., Inguaggiato, C., and Wanner, C.: Exploration of orogenic, fault-hosted geothermal systems using an integrated, multi-disciplinary approach., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13261, https://doi.org/10.5194/egusphere-egu21-13261, 2021.

There is no evidence of hydrothermal fluid discharges in the surficial environment of the Canary Islands, the only Spanish territory with potential high enthalpy geothermal resource, with the exception of the Teide fumaroles.

In 2011 and 2014 several geochemical and geophysical studies were carried out across 4 mining licenses on the island of Tenerife (Abeque, Berolo, Guayafanta, Garehagua) for geothermal exploration purposes. The geothermal exploration licenses known as Garehagua and Abeque, located on the south ridge and on the northwest ridge of the island of Tenerife respectively, showed the highest geothermal potential of the studied areas. It was decided to carry out several more detailed studies in the areas with the most significant anomalies to better characterize the potential for economic exploitation.

Three surface geochemical surveys each with an average measurement spacing of ~40 m were conducted, and allowed for a mesh resolution of 10 m x 10 m: a mesh size of a much higher spatial resolution than typical grids for surveys of potentially prospective or known geothermal areas. An area called ‘’Madre del Agua’’, located in the northern zone of the Gareagua mining license was prioritised for attention due to i) observed geochemical anomalies at the soil surface; ii) the prominent low-resistivity structure interpreted as a clay alteration cap, and; iii) the positive correlation between thickness of clay alteration cap and helium emission. This study area covers ~0.7 km². The second area selected for detailed study is located inside the Abeque mining license. The spatial correlation between the helium enrichment and the endogenous CO₂ component of Abeque motivated the selection of this study area called ‘’Abeque Detalle’’, which covers ⁓0.8 km². The third study area called ‘’Fuente del Valle’’ (⁓0.6 km²) was motivated by the observation of significant values ​​of helium anomalies in the Garehagua study area that were measured on the surface in the vertical of a bubbling of endogenous gases at depth, ~2,850 m from the entrance of the Fuente del Valle gallery.

The studies were completed from July to September 2018 (Madre del Agua and Abeque Detalle) and from January to March 2019 (Fuente del Valle). During the survey 1065 sampling sites were made, distributed among the three surveys: 362 points in Madre del Agua, 377 in Abeque Detalle and 326 in Fuente del Valle. At each sampling site the soil CO₂ efflux and ²²²Rn activity were measured in-situ and He and H₂ were sampled at 40 cm depth and analysed in the lab. The spatial distribution of soil gases of the three study areas confirm the presence of relative enrichment of non-reactive and/or highly mobile gases in the soil gas atmosphere such as He and CO₂, that suggests the existence of a significant contribution of deep-seated gases.

How to cite: Martín-Lorenzo, A., Rodríguez, F., Alonso, M., Amonte, C., Melián, G. V., Asensio-Ramos, M., Padrón, E., Hernández, P. A., and Pérez, N. M.: A detailed soil gas physical-chemical survey for geothermal exploration at Tenerife, Canary Islands., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15066, https://doi.org/10.5194/egusphere-egu21-15066, 2021.

SW England is the most prospective region in the UK for the development of deep geothermal energy as it has highest heat flow values (c. 120 mW m^-2) and predicted temperatures greater than 190 ^oC at 5 km depth. The United Downs Deep Geothermal Project (UDDGP), situated near Redruth in Cornwall, is the first deep geothermal power project to commence in the UK. Two deviated geothermal wells, UD-1 (5058 m TVD) and UD-2 (2214 m TVD), were completed in 2019 and intersect the NNW-SSE-trending Porthtowan Fault Zone (PTFZ) within the Early Permian Cornubian Batholith.

The Cornubian Batholith is composite and can be divided into five granite types that were formed by variable source melting and fractionation [1]. These processes were the primary control on the heterogeneous distribution of U, Th and K that underpins heat production in the granite. Previous high resolution airborne gamma-ray data has demonstrated the spatial variation of near-surface granite heat production [2], and the CSM Hot Dry Rock Project (1977-1991) provided U, Th and K distributions to depths of 2600 m in the Carnmenellis Granite [3]. However, uncertainties in: (i) U, Th and K content in the deeper batholith, (ii) thermal conductivity are still challenges to modelling the high heat flow.

Preliminary evaluation of UD-1 downhole spectral gamma data (900-5057 m) indicates the presence of three major granite types on the basis of contrasting U and Th characteristics. QEMSCAN mineralogical analysis of cuttings (720 – 5057 m) demonstrates the overwhelming dominance of two mica (G1) and muscovite (G2) granites and little expression of biotite (G3) granites. U- and Th- bearing accessory minerals include monazite, zircon and apatite, with the appearance of allanite and titanite in the deeper granites. Representivity analysis between various cutting fractions show no systematic bias in the major mineral components.

There is a substantial increase in Th below 3000 m that indicates the deeper parts of the batholith are likely to contribute substantially to overall heat production. Monazite is the primary source for Th and has a close association with micas. Mineralogical, mineral chemical, whole-rock geochemical and coupled thermal conductivity analysis is ongoing to improve understanding of the construction of this part of the Cornubian Batholith and its implications for the regional thermal resource and sub-surface temperature evaluation.

References:
[1]Simons B et al. (2016) Lithos, 260: 76-94
[2]Beamish D and Busby J (2016) Geothermal Energy, 4.1:4
[3]Parker R (1989) Pergamon, 621.44

How to cite: Dalby, C., Shail, R., Batchelor, T., Cotton, L., Gutmanis, J., Rollinson, G., Wall, F., and Hickey, J.: Deep geothermal energy from the Cornubian Batholith: preliminary lithological and heat flow insights from the United Downs Deep Geothermal Power Project., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15875, https://doi.org/10.5194/egusphere-egu21-15875, 2021.

For successful exploitation of geothermal reservoirs, temperature and transmissibility are key factors. The Molasse Basin in Germany is a region in which these requirements are frequently fulfilled. In particular, the Upper Jurassic Malm aquifer, which benefits from high permeability due to locally intense karstification, hosts a large number of successful geothermal projects. Most of these are located close to Munich and the “Stadtwerke München (SWM)” intends to use this potential to generate most of the district heating demands from geothermal plants by 2040.

We use geophysical logging data and sidewall cores to analyse the spatial distribution of reservoir properties that determine porosity, permeability, and temperature distribution. The data are derived from six deviated wells drilled from one well site. The reservoir rocks are separated by faults and lie in three different tectonic blocks. The datasets include image logs, GR, sonic velocities, temperature, flowmeter- and mud logs. We not only focus on correlations between rock porosity and matrix permeability, but also on how permeability provided by fractures and karstification correlate with inflow zones and reservoir temperature. In addition, we correlate individual parameters with respect to their lithology, dolomitisation and the rock’s image fabric type, adapted from Steiner and Böhm (2011).  

Our results show that fracture intensity and orientations vary strongly, between and within individual wells. However, we observed local trends between fracture systems and rock properties. For instance fracture intensities and v_p velocities (implying lower porosities) are higher in rock sections classified as dolomites without bedding contacts. As these homogeneous-appearing dolomites increase, from N to S, the mean fracture intensities and v_p velocities also increase. Furthermore, we observed most frequently substantial karstification in dolomites and dolomitic limestones. Nevertheless, an opposing trend for the percentage of substantial karstification can be also found, i.e., the amount of massive karstification is higher in the northern wells. The interpretation of flowmeter measurements show that the main inflow zones concentrate in those Upper Malm sections that are characterised by karstification and/or intense fracturing.

In the next step, we will correlate laboratory measurements of outcrop- and reservoir samples (e.g. porosity, permeability, and mechanical rock properties) with the logging data. The aim is to test the degree to which analogue samples can contribute to reservoir characterization in the Upper Jurassic Malm Aquifer (Bauer et al., 2017).

This work is carried out in the research project REgine "Geophysical-geological based reservoir engineering for deep-seated carbonates" and is financed by the German Federal Ministry for Economic Affairs and Energy (FKZ: 0324332B).

Bauer, J. F., Krumbholz, M., Meier, S., and Tanner, D. C.: Predictability of properties of a fractured geothermal reservoir: The opportunities and limitations of an outcrop analogue study, Geothermal Energy, 5, 24, https://doi.org/10.1186/s40517-017-0081-0, 2017.

Steiner, U., Böhm, F.: Lithofacies and Structure in Imagelogs of Carbonates and their Reservoir Implications in Southern Germany. Extended Abstract 1st Sustainable Earth Sciences Conference & Exhibition – Technologies for Sustainable Use of the Deep Sub-surface, Valencia, Spain, 8-11 November, 2011.

How to cite: Bauer, J., Pfrang, D., and Krumbholz, M.: Characterisation of a highly heterogeneous geothermal reservoir based on geophysical well logs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2205, https://doi.org/10.5194/egusphere-egu21-2205, 2021.

The Molasse Basin is one of the most promising areas for deep geothermal exploration in Germany and a very ambitious project in this region is to power the entire district heating system of the city of Munich with renewable energies by 2040; a major part of this will consist of geothermal energy. As part of a joint project (financed by the German Federal Ministry For Economic Affairs And Energy; FKZ 0324332B) the Leibniz Institute for Applied Geophysics (LIAG) works together with the Munich City Utilities (Stadtwerke München), to improve reservoir characterization and sustainable reservoir exploration within the German Molasse Basin. The target horizon for hydrothermal exploration is the aquifer in the Upper Jurassic carbonates. A major problem is the strong heterogeneity of the carbonates. Compared to quantity and quality of the structural data of the reservoir, the database of reservoir properties such as density, porosity and permeability, which describe the geothermal potential, is insufficient. Therefore, it is necessary to generate such data in order to improve the value of the structural information. A 3D seismic survey cannot only provide structural information, but also important reservoir properties such as elastic parameters and seismic attributes. One of the most important attributes is the acoustic impedance, which can be determined with a seismic inversion and used to estimate a porosity volume.

The data basis for this study was the 170km² GRAME-3D seismic survey measured in Munich, a structural geological model, and drilling and logging data from the geothermal site “Schäftlarnstraße”.

The inversion results show low impedance values at the top of the reservoir, but also at the middle part. Spatially, the intermediate block of the Munich fault shows low values but also the eastern part of the hanging wall block and the western part of the footwall block. Based on a well correlation a relationship between acoustic impedance and porosity could be determined and a 3D porosity volume was calculated. In the upper part but also in the middle part of the reservoir areas with increased porosity (>10%) are shown, which might indicate a high geothermal potential.

For a better classification, an attribute analysis was performed. The intermediate block and the eastern part of the hanging wall block show strongly fractured rocks. In contrast, there are hardly any conspicuous features in the western part of the footwall block, although high porosities are also expected here. This suggests that the presence of faults is not the only factor favoring high porosities in carbonates. More likely is a combination with karstification processes, which is why even areas that do not show enhanced tectonic deformation have high porosities.

How to cite: Wadas, S. and von Hartmann, H.: Porosity estimation and characterization of a geothermal carbonate reservoir in the South German Molasse Basin based on seismic inversion and attribute analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7028, https://doi.org/10.5194/egusphere-egu21-7028, 2021.

New heat flow measurements collected throughout the Auka and JaichMaa Ja' ag' hydrothermal vent fields in the central graben of the Southern Pescadero Basin, southern Gulf of California, indicate that upflow of hydrothermal fluids associated with active rifting dissipate heat in excess of 10 W/m² around faults that have a few tens-of-meters of displacement. Heat flow anomalies slowly decay to background values of ~2 W/m² at distances of ~1 km from these faults following an inverse square-root distance law. We develop a physical model of the Auka vent field based on the fundamental Green's function solution of the heat equation. The model includes the effects of circulation in the porous networks of faults and the lateral seepage of geothermal brines through the fault walls to surrounding hemipelagic sediments.  We use an optimal fitting method to estimate the reservoir depth, permeability, and circulation rate. Our model indicates the heat source is at a depth of ~5.7 km; permeability and flow rates in the fracture system are ~10^-14 m² and 10^-7 m/s, respectively, and ~10^-16 m² and 10^-8 m/s in the basin aquitards, respectively. Model scaling laws point to the importance of faults in controlling sediment-hosted vent fields and slow circulation throughout low permeability sediments in controlling the brine's chemistry. Although the fault model seems appropriate and straightforward for the Pescadero vents, it does seem to be the exception to the other known sediment-hosted vent fields in the Pacific.

How to cite: Negrete-Aranda, R., Neumann, F., Contreras, J., Harris, R. N., Spelz, R. M., Zierenberg, R., and Caress, D. W.: Transport of Heat by Hydrothermal Circulation in a Young Rift Setting:  Observations from the Auka and JaichMaa Ja'ag' vent Field in the Pescadero Basin, Southern Gulf of California., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3525, https://doi.org/10.5194/egusphere-egu21-3525, 2021.

Most recently, energy consumption around the world steps into a new situation divided by petroleum, natural gas, coal and new energy. Fossil fuels are disputed for pollution and CO₂ emission, and geothermal energy is popular as a clean, ecofriendly and renewable new energy, which can be used for power generation or direct application (e.g. bathing, building heating).

Gonghe Basin, located in the western part of China, has been thought as a potential geothermal field since 1989. To investigate geothermal distribution in Gonghe Basin and adjacent area, magnetic data is used in this paper. Firstly, we proposed an improved magnetic interface inversion method based on traditional Park-Oldenburg method. This improved method introduces dual geological interfaces instead of one interface, variable magnetic susceptibility instead of constant magnetic susceptibility and upward continuation in a form equivalent to inversion iteration in the Fourier domain instead of the divergent, downward continuation term, to improve suitability and precision of the inversion method. Then Curie point depth (CPD) map and heat flow map could be deduced from magnetic data through the improved Park-Oldenburg method.

The CPDs range from 16 to 25.5 km and heat flow values range from 61 to 91 mW/m². What's more, we take faults and seismic activities into account, we find that study area has greater geothermal potential in eastern part with shallower CPD, higher heat flow values and more active subsurface structure. Considering with known geothermal value in actual measurement, the results indicate high heat flow value in Gonghe Basin is coaction of high thermal background, radiogenic heat and partial geothermal anomalous heat source. 

How to cite: Wang, Z. and Zeng, Z.: Curie point depth and heat flow maps deduced from magnetic data of Gonghe Basin, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4140, https://doi.org/10.5194/egusphere-egu21-4140, 2021.

The Theistareykir geothermal field is located at the intersection between the active Northern Rift Zone and the active Tjörnes Fracture Zone in NE Iceland, and its study is of vital importance for further development of local and regional geothermal resources. Since autumn 2017, a seismic network consisting of 21 stations was deployed to monitor the high temperature Theistareykir geothermal field (Iceland). This seismic network belongs to a set of multiparameter networks installed to better understand the underlying structure and behavior of the geothermal reservoir under exploitation.

In this framework, we use the continuous ambient noise seismic records between October 2017 and October 2019 to compute a 3D shear wave velocity model of the geothermal field and to detect possible stress changes due to the injection and production activities. We compute the phase auto- and cross-correlations of the vertical component recordings, measure the Rayleigh wave group velocity dispersion curves, and obtain 2D group velocity maps between 1 and 5 s.  The 2D group-velocity maps are used to construct regionalized dispersion curves which are then inverted using a Neighborhood Algorithm to retrieve the 3D Vs model of Theistareykir. We observe various underground structures and identify the locations of possible magmatic or hydrothermal bodies in light of available and newly acquired geological and geophysical data. In addition, we analyze the short and long term temporal evolution of the phase auto-correlations using coda wave interferometry and discuss their relationship to the geothermal field operations. We notice a slightly stronger velocity reduction around the production site in comparison to the surrounding regions.

How to cite: Toledo, T., Obermann, A., Jousset, P., Verdel, A., Martins, J., Erbas, K., Júlíusson, E., Mortensen, A., and Krawczyk, C.: Ambient seismic noise monitoring and imaging at the Theistareykir geothermal field (Iceland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12741, https://doi.org/10.5194/egusphere-egu21-12741, 2021.

Geophysical process simulations pose several challenges including the determination of i) the rock properties, ii) the underlying physical process, and iii) the spatial and temporal domain that needs to be considered.

Often it is not feasible or impossible to include the entire complexity of the given application. Hence, we need to evaluate the consequences of neglecting certain processes, properties, etc. by using, for instance, sensitivity analyses. However, this evaluation is for basin-scale application non-trivial due to the high computational costs associated with them. These high costs arise from the high-dimensional character of basin-scale applications in the parameter, spatial, and temporal domain.

Therefore, this evaluation is often not performed or via computationally fast algorithms as, for example, the local sensitivity analysis. The problem with local sensitivity analyses is that they cannot account for parameter correlations. Thus, a global sensitivity analysis is preferential. Unfortunately, global sensitivity analyses are computationally demanding.

To allow the usage of global sensitivity analysis for a better evaluation of the changes in the influencing parameters, we construct in this work a surrogate model via the reduced basis method.

The reduced basis method is a model order reduction technique that is physics-preserving.  Hence, we are able to retrieve the entire state variable (i.e. temperature) instead of being restricted to the observation space.

To showcase the benefits of this methodology, we demonstrate with the Central European Basin System how the influences of the thermal rock properties change when moving from a steady-state to a transient system.

Furthermore, we use the case study of the Alpine Region to highlight the influences of the spatial distribution of measurements on the model response. This latter aspect is especially important since measurements are often used to calibrate and validate a given geological model. Thus, it is crucial to determine which amount of bias is introduced through our commonly unequal data distribution.

How to cite: Degen, D., Cacace, M., Spooner, C., Scheck-Wenderoth, M., and Wellmann, F.: Benefits of Global Sensitivity Analysis and Reduced Order Modeling for Basin-Scale Process Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7036, https://doi.org/10.5194/egusphere-egu21-7036, 2021.

Chemical stimulation of geothermal wells to remove drilling mud and to increase the connection to the reservoir are state of the art. There is hardly any deep geothermal well in the carbonates of the upper jurassic in the pre alpine foreland basin which was not developed using one or more pulses of acid. Several tons of acid are injected into the borehole and followed by a chaser to push the acid into the reservoir. Given the wide use of chemical stimulation measures, mass balance data for the stimulation is rare. This might be due to a rather simple reaction mechanism and the assumption that there is a full stoichiometric reaction and all injected acid is recovered. The efficiency of the stimulation is assessed based on the hydraulic properties derived from the short-term pumping tests following the stimulation. This project compares the full mass balance for chemical stimulation measures and the temporal development of the concentration of relevant ions during the pumping test after stimulation. The data was collected at several sites with a temporal resolution of down to 30 mins. The data includes multiple stimulations as well as stimulation with varying acids and different setup. Using this data set we want to answer the questions whether the acid is fully recovered, whether the assumption of full stochiometric reaction is valid, whether there is a difference in the transport of reactive and conservative ions, what additional value a hydrochemical analysis could add and whether on-site measurements could substitute costly measurements. The evaluation shows a distinct behaviour of the temporal development of the chloride concentration (after stimulation with hydrochloric acid) which can be described by a bi-exponential fit. The fitting parameters of the two exponential terms are getting closer with each stimulation indicating a reduced heterogeneity along the accessible flow paths around the borehole. A comparison of the full scale analysis with on-site sensors was sometimes not possible because the sensors showed a drift during the experiment or were poorly calibrated. As calcium, magnesium, and chloride ion concentrations showed different behaviour, electrical conductivity is not able to cover the full development. The mass balance indicates that a full recovery of the injected acid might take significantly longer than the short term pumping tests. Hydrochemical monitoring provides additional and relevant data about the reservoir in the surrounding of the borehole and allows important predictions about the long-term behaviour, especially if the borehole is used as injection well. For routine applications improved sensors and fast (and cheap) on-site analysis is required.

How to cite: Kaplar, F. and Baumann, T.: Comparative study of chemical stimulation at geothermal wells in the carbonates of the upper jurassic in the Bavarian Molasse Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13172, https://doi.org/10.5194/egusphere-egu21-13172, 2021.

The geothermal environment is an assembly of heterogeneous geological settings and complex interactions among different phases of rock and fluid medium. The artificial activities of energy production could further interplay with the on-going natural processes within volcanos, hotspots, and other geothermal areas to result in spatiotemporal signatures of displacements near the surface. Here, we study the temporal ground deformation near a geothermal site through processing Interferometric Synthetic Aperture Radar (InSAR) time-series data obtained over the past decades, as reconciled with the nearby GPS station. To interpret these signals and potentially reveal the reservoir’s temporal activity, we employ state-of-art finite element models (FEMs) to simulate a more realistic crustal domain near the energy-production zone with irregular reservoir geometry, distributed rock materials, and surface topography. Linear Bayesian geodetic inversion and Green’s function library area were adopted to quantify the cause of surface subsidence, as compared to the documented production history. Our study demonstrates an unprecedented approach to precisely simulate the elastic deformation caused by geothermal energy extraction and pumping, providing an important platform to further explore the in-depth evolving stress state and its relation to surrounding induced and natural seismicity.

How to cite: Tung, S. and Feigl, K.: Modeling surface deformation of geothermal environments with high-fidelity finite element models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13413, https://doi.org/10.5194/egusphere-egu21-13413, 2021.

The Los Humeros Volcanic Complex (LHVC) is an active Quaternary caldera system in the Trans Mexican Volcanic Belt, characterized by two major caldera-forming events, Los Humeros (164 000 years ago) and Los Potreros (69 000 years ago). This site is also subjected to numerous episodes of post-caldera bi-modal volcanism during Holocene period (8 000 years – 3 000 years old). The volcanic complex hosts an active geothermal field which has been under commercial exploitation for the last 30 years. Latest geochemical, petrological and geochronological investigations consider the geothermal activity in the LHVC to be the result of an underlying complex magma plumbing system, characterized by numerous short-lived, shallow magma storage zones. Geothermal wells in the LHVC have encountered variable temperatures within depths of 2000 m, ranging from 170 °C at some areas to above 350 °C in the neighboring areas. To explain this anomalous temperature distribution and evaluate the thermal footprint of different volcanic episodes, we reconstructed the thermal history of the LHVC for a period of 182 000 years considering the spatially and temporally-varying nature of the heat sources. Our numerical model is constrained by information of depths, ages and volumes of the magma reservoirs, obtained from the geochemical and thermo-barometric modeling of the erupted material. The simulated present-day temperature state agrees well with the measured temperature data in the Los Humeros geothermal wells and can be used for identifying locations with anomalous temperature distribution. This integrated modeling approach, whereby numerical model is constrained by field-based geochemical information is essential in exploration geothermal fields, where limited borehole data is available, and promising for identifying potential locations of super-hot geothermal fluids.

How to cite: Deb, P., Giordano, G., Shi, X., Lucci, F., Clauser, C., and Calcagno, P.: Thermal modeling in active poly-phased calderas: case study of Los Humeros, Mexico, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15793, https://doi.org/10.5194/egusphere-egu21-15793, 2021.

              When producing heat from a geothermal well, the produced water cools down in the heat exchanger, and experiencing a lower pressure in the surface processing-facility (1 – 10 bar) than in the reservoir (100 – 300 bar). The decrease in pressure may cause gas to come out of solution. This decrease in temperature and degassing of the produced water may cause precipitation and dissolution (mineralization) to occur. After the produced water is cooled down, it is reinjected into the reservoir through an injection well. Mineralization in the reservoir restricts the flow path of the injected water, resulting in reduced injectivity. Consequently, more energy is required by the injection pump, which results in additional costs, and thereby reduces the project’s economic return.            
              When numerically modeling mineralization in a geothermal reservoir, accounting for the reaction kinetics can be computationally expensive. The simulations can be made less expensive by assuming local equilibrium between the reactants and reaction-products; but using this approach might give results that are not in agreement with experimental findings.
              Here we present an analytical model for mineral precipitation in a low-enthalpy geothermal reservoir. We compare the kinetics of the relevant reaction terms with respect to the transport terms (heat and flow) to determine whether the local equilibrium approach (LEA) or kinetics approach (KA) is appropriate for modeling a specific reaction. We focus on the near-wellbore region in the reservoir, where precipitation can behave as a ‘skin’; when assuming radial-flow, precipitation in the near-wellbore region has a more dramatic impact on the injectivity than precipitation further downstream in the reservoir.      
              Using numerical simulations we validate the approach to use different methods of geochemical modelling based on the reaction speed and its potential impact on computation time.
              Based on our analysis on mineralization in the near-wellbore-region, the three different reaction regimes can be distinguished when comparing the time-scale of reaction to the time-scale of transport, viz.: (1) fast reactions (mineralization can be considered instantaneous and modelling these reactions using LEA or KA does not lead to significantly different simulation results); (2) very slow reactions (no significant change in ion concentrations in the region of interest, whether these reactions are modelled using LEA or KA); (3) reaction/transport intermediate zone (using LEA leads to significantly different simulation results compared to KA).
              Accounting for these classifications allows simplification of the current numerical geochemical-models, while still accounting for relevant kinetics of mineralization. This approach was tested using a numerical model of precipitation in a geothermal reservoir.              

How to cite: Hussain, A., Khoshnevis, N., Meulenbroek, B., Van der Star, W., Bruining, H., Claringbould, J., Reerink, A., and Wolf, K.-H.: Modelling Mineral-Scaling in Geothermal Reservoirs Using Both a Local Equilibrium and a Kinetics Approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16033, https://doi.org/10.5194/egusphere-egu21-16033, 2021.