European Geologist Journal 56

Science-based data service to accelerate geothermal developments in Hungary

 

by Annamária Nádor ¹

¹ Senior Geologist; Supervisory Authority for Regulatory Affairs

Contact: annamaria.nador@sztfh.hu

Abstract

Hungary’s rich geothermal resources provide a real option to tackle the present energy crisis, decrease the country’s high gas dependency and decarbonise its heating sector. Nevertheless, geothermal project development faces some barriers, one of the most important ones is the geological risk of the unknown reservoir properties. One powerful tool to mitigate this risk is to increase the knowledge of the subsurface and provide geoscientific data availability to project designers. The presented Hungarian case study shows a systematic development of such data service, comprising a public web-map based geothermal information system (OGRE) and tailor-data packages developed on the basis of an indicator system that considers the 3 most important factors: reservoir types (R), heat market conditions (H) and the rate of exploration (S).

This work is licensed under a Creative Commons Attribution 4.0 International License.

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1. Introduction

Hungary’s excellent geothermal potential – due to its favourable geological setting, including high heat flux and an above average geothermal gradient, coupled with extensive and deep-lying aquifers – is well known. Despite the fact that Hungary is among the top 5 countries in Europe in direct use (1,02 GW_th installed capacity, 2508,26 GWh/yr annual production in 2021 [1]), there are still a lot of untapped opportunities especially in the heating sector. The current energy crisis urged to take this chance, as 82% of Hungary’s annual gas consumption (9,4 BCM) is imported from Russia, and the share of gas in heating buildings is about 50%. Recent analyses [2] revealed, that even with current technologies the present 6,5 % share of geothermal (3090 TJ) in the heating sector could be increased to 25-30% within 5-10 years, thus geothermal could replace about 1 BCM gas, primarily in the residential heating sector.

Numerous barriers of deep geothermal project development have been identified, but it is commonly agreed that one of the most important hurdles is the high geological risk at the exploration phases due to uncertainties in the geological knowledge of the subsurface, coupled with significant capital expenditures resulting from the high drilling costs. This unfortunate matching of high risks and high costs often discourage investors and impedes project development. One way to deal with this problem is the establishment of geological risk mitigation schemes [3] which successfully operate in a few European countries, however, requires significant public and/or private funds to function. The other alternative is to increase the knowledge of the subsurface and make geoscientific data publicly available, thus minimising the risks that a borehole does not discover the suitable reservoir. Collecting, assessing, storing, and making geoscientific data openly available is generally the role of National Geological Surveys, therefore their role in supporting the development of successful geothermal projects is inevitable. This paper presents a showcase of a systematic approach of building and making geoscientific data accessible to assist geothermal project development in Hungary. This organised work followed the FAIR database principles as much as possible (Findable, Accessible, Interoperable, Re-usable).

2. Public data service to de-risk geothermal projects

2.1. Online geothermal information platform (“OGRE”)

Hungary’s first online Geothermal Information System (OGRE) aims to provide up-to-date and reliable geological, hydrogeological and geophysical data and information about the country’s geothermal energy resources via a user-friendly  website with public access. The GIS based web-map system is available in Hungarian and English. It was developed by the Hungarian Geological Survey from state funds and was launched in 2020. The system is a thematic arrangement and update of already existing geological, geophysical, and hydrogeological databases relevant to geothermal energy. It was established with the aim to help the preparatory work of national and international consortia aiming to invest into new geothermal projects in Hungary, as well as the every-day work of policy makers. Furthermore, it aims to assist higher level education and also provide useful information to the public interested in geothermal energy. Maps presented on the portal are based on regional geoscientific models, therefore they provide a large-scale overview about the geothermal conditions of a certain territory; however, they do not replace detailed exploration and pre-feasibility studies necessary for a concrete project at local scale.

The web-map system is comprised of a set of maps edited for the territory of the entire country (e.g. geological horizons bounding the most important geothermal aquifers, isotherm maps characterising the subsurface temperature conditions, maps showing the 3D spatial distribution of the most important geothermal reservoirs, etc.); point features (e.g. thermal water wells, boreholes, locations of geothermal projects, etc.) and polygons (e.g. thermal groundwater bodies, concessional areas, etc.). These are arranged into various thematic groups, which can be visualised up to request and can be combined with each other. The different thematic groups and their specific layers generally show metadata. An exception is the group of thermal water wells, where the system provides detailed data of 1720 wells (e.g. depth of screened intervals, aquifer lithology, groundwater level, yield, temperature, hydrogeochemical character, utilisation type, etc.).

With a detailed map series of geophysical coverage, as well as maps showing the location of deep boreholes (including hydrocarbon exploration wells), OGRE provides a unique opportunity to search for data of a certain territory for a detailed prospection. Data themselves are not provided through the portal, but are available at the Sate Geological, Geophysical and Mining Data Store.

2.2. Planning geothermal data packages

Whilst OGRE provides an exclusive opportunity to get an in-depth overview of Hungary’s geothermal conditions and the most prosperous areas, it does not make data available. Nevertheless, with the growing interest to develop deep geothermal projects – which boomed after the amendment of the Mining Law in March 2023 – the need to get data available in a quick and effective way became evident. To meet this demand, it was decided to prepare different types of data packages that project developers can use via a data room service.

As the greening of district heating and residential heat is one of the top priorities of Hungary’s energy strategy, the compilation of data packages focused on potential areas suitable for such developments. To get an objective and comprehensive list of potential sites, first an independent indicator system has been established. To have a successful (direct use) geothermal project, the most important, yet not the only requirement is to discover a suitable reservoir that provides the necessary temperature and yield to feed the future heating plant. As heat cannot be transported on long distances, it is of ultimate importance to have an adequate heat market nearby to the source as well. This factor is unfortunately often neglected or underestimated, leading to situations where a successful well drilled at excessive costs discharges large amounts of hot water in the middle of uninhabited areas for no use. Finally, the level of geological knowledge of a future exploration area matters a lot. Dense data coverage minimizes the geological risk and only reinterpretation of some old data might be necessary, whilst a wildcat drilling holds significant risks, which can be reduced by pre-drilling surface exploration (e.g. new seismic measurements).

To encompass all these factors that have primary role on a successful geothermal project development, a numerical indicator system has been established that typifies future project sites (in the Hungarian case these are cities and their 15 km radius) assessing the type of geothermal reservoirs that defines the basic geological parameters of a future project (R), the heat market conditions (H), and the rate of surveillance (S). Using this system, each future project site can be characterised by a numerical code of 3 digits (Rx, Hx, Sx) (Fig 1).

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R classes -Reservoir types

Given the geology and geothermal conditions of Hungary [4] [5], there are 2 main types of geothermal reservoirs with different characteristics (Fig. 2).

The majority and most well-known porous geothermal aquifers are represented by few tens to hundred m thick regionally extended and hydraulically interconnected sand bodies that deposited during shelf progradation, which represents the latest stages of the filling up of the Pannonian basin during the Late Miocene and Pliocene [6]. The best reservoirs are found at depths from 500 to 2000 m, where the temperature ranges from 40 to 110 °C [7], [8]. These porous “basin fill” reservoirs are widely used for direct use purposes, mostly in agriculture (greenhouse heating) and space / district heating. As these geothermal aquifers are widespread and explored by hundreds of active thermal water wells, the exploration risk is relatively low. Nevertheless, many of these reservoirs are already overexploited, characterized by decreasing piezometric levels due to high abstraction rates and insufficient reinjection.

The other major type of geothermal reservoirs is represented by different types of carbonates and crystalline rocks, such as limestones, dolomites, granites of Palaeozoic and Mesozoic age that form the basement of the Pannonian basin beneath the thick Neogene sedimentary sequences. They have an extremely complex structural pattern, arranged into nappes along thrust sheets, dissected by strike-slip and normal faults, associated with the multi-phase tectonic development of the Pannonian basin [9], [10]. These tectonic zones are important targets of geothermal exploration, as they represent regions with significantly increased permeability. The other valuable exploration target comprises basement carbonates that karstified during their geological evolution, thus possessed an increased secondary porosity as well. At the basement depth (around -2000 m or more) temperature can exceed 100–150 °C [11]. The coupled high temperature and high permeability makes these basement rocks excellent and prosperous reservoirs for larger scale district heating, or even combined heat and power projects which require higher capacities. Nevertheless, the exploration risks are much higher compared to the above lying porous basin fill reservoirs, as the discovery of the spatially limited fracture/karstic zones requires sophisticated subsurface models and geophysical exploration methods (mostly 2-3D seismic reflections).

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Considering the above brief reservoir characterisation, the following classes have been identified:

• R1 – porous;
• R2 – karstic;
• R3 – fractured crystalline;
• R4 – not suitable (uplifted areas).

H classes – Heat market conditions

As it was highlighted before, matching the source with demand is the key for a successful geothermal project. Assessing heat market conditions, the following categories were defined:

• H1 – Cities with existing district heating infrastructure (sub-categories defined according to installed capacity: above, and below 10MW_th);
• H2 – Significant industrial heat market;
• H3 – Settlements with considerable residential heat market (sub-categories defined according to population: above 15 000 and between 10 000 and 15 000);
• H4 – No / insignificant heat market.

S classes – Surveillance

The probability of success of a drilling (i.e., that it hits the target reservoir rock with expected temperature and yield) can be significantly increased by raising the level of geological knowledge of the subsurface. Thus, the rate of exploration pre-determines the success of the project. Therefore, the following categories were defined:

• S1 – A well explored area, no additional data is necessary; the future drilling site can be located based on existing data and knowledge;
• S2 – A well explored area, however reinterpretation of old data is necessary to increase the consistency of the geological model;
• S3 – Underexplored area, new measurements are necessary to set up a trustworthy geological model.

 

3. Discussion

It is important to note that the different R-H-S classes do not imply any “quality” assessment, simply they characterize the given settlement and its surroundings as a future project site. Thus, the list of settlements can be adaptably modified at any time by applying different screening categories according to different strategic priorities. The numerical coding makes easy to list settlements in an objective way to answer multiple questions, e.g.:

1. Which are the cities, where the switching of district heating to geothermal is feasible with potentials for high yields and temperatures and moderate exploration costs (H1, R2, S2);
2. Where are significant industrial heat demands, whereas the project developer is ready to take higher risks and invest into exploration (H2, R1-3, S3);
3. Where are smaller settlements suitable for lower temperature town heating systems, where no extra survey is necessary (H3, F1, S1);

Applying the above-described classification scheme in Hungary, altogether 158 settlements and their surroundings were classified as potential targets for geothermal developments. Some screening results as examples are shown on Figures 3. and 4.

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The classification system also allows for the identification of potential areas with existing heat demand, where additional research is needed to increase the knowledge of the subsurface, in other words to reduce the risk of unsuccessful drilling. In many cases the potential investors (e.g., smaller municipalities) do not have adequate resources to perform this pre-drilling exploration, which impedes project development. Nevertheless, if such focussed research is considered as a geological responsibility of the state, and exploration survey data are available for the public, it increases the willingness to invest into geothermal. This has happened in Hungary, where state financed seismic campaigns are ongoing (field surveys and interpretation) on areas where little/no data is available (S3) to increase the knowledge of the subsurface, thus make the areas stimulating future project developments.

The above discussed classification system also provided the basis for determining the list of settlements, for which so called data packages are being compiled that will be available through a Geothermal Data Room opening in 2023 Q4. There are 2 types of data packages:

1. Basic data packages compiled for all prosperous 158 areas that contain a systematically arranged geological, hydrogeological, and geothermal data.
2. Advanced data packages that also contain reinterpreted data and expert assessments.

The content of the different types of data packages, as well as data available through OGRE are summarized in Table 1.

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Table 1: Content and data type of OGRE and the data packages. Y/N refers to data availability: Y- such data included and N- such data not included.

	OGRE	Basic data package	Advanced data package
Basic info
Location, basic topo map	N	Y	Y
Nature protection areas	N	Y	Y
Exploration (metdata)
Hydrocarbonexploration area, mining plot	N	Y	Y
Geothermal protection zone	Y	Y	Y
Reports	N	Y	Y
CH well documentation	N	Y	Y
Borehole locations	Y	Y	Y
Geophysical exploration (2-3D seismic, magnetolellurics, gravimetry)	Y	Y	Y
Geology, geophysics
Boreholes (lithostratigraphy)	N	Y	Y
Hydrogeological well documentattion	N	Y	Y
Hydrocarbon well book	N	Y	Y
Well logs	N	Y	Y
Geological horizons	Y	Y	Y
Geological 3D model, reinterpreted geological horizons	N	N	Y
Other thematic maps (e.g. tectonics)	N	N	Y
2-3D seismics (measured and interpreted)	N	Y	Y
Geological cross sections	N	Y	Y
Subsurface temperature maps	Y	Y	Y
Geothermal data (heatflux, heat conductivity, geothermal gradient, etc.)	N	Y	Y
3D subsurface temperature model	N	N	Y
List of relevant publications	N	Y	Y
Hydrogeology
Thermal water well basic data (yield, temperature, screened intervals, utilization)	Y	Y	Y
Thermal water well hydrgeochemisrty (TDS, water type, CH4 content)	Y	Y	Y
Water level in wells (basic and operational)	N	Y	Y
Characterisation of thermal aquifers	N	N	Y

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4. Conclusions

Making reliable and up-to-date geoscientific data publicly available is considered a geological responsibility of the state in many European countries and is often a decisive task of national geological surveys. Tailor-made databases of basic and reinterpreted data make possible to better delineate potential geothermal reservoirs and understand their properties, thus it is an important tool to de-risk geothermal project development. The presented Hungarian case introduced successive steps of public data service. The web-map based online geothermal information system (OGRE) provides a large-scale overview about the geothermal conditions of the country. Based on a set of geological and geothermal maps, it is possible to delineate prosperous areas for future exploration, where metadata of the available boreholes, geophysical measurements, hydrogeological data, etc. are also available. As a subsequent step, potential locations within these favourable areas have been categorised according to 3 criteria (reservoir type, heat market and rate of surveillance) and data themselves have been organised into data packages, which will be available through a data room service in the near future.

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References

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This article has been published in European Geologist Journal 56 – Geoscience in policy making: Past experience, current practice and future opportunities

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