Today, increasing energy consumption, tightening environmental requirements and, in some cases, countries’ energy‑security exposure, particularly in the Central‑Eastern European region, present serious challenges. Under the support of the INTERREG Central Europe programme, the TRANSGEO project has launched an investigation into an innovative solution to this problem, evaluating the opportunity of converting abandoned hydrocarbon wells into geothermal energy sources.
The project examines abandoned hydrocarbon wells in five countries—Germany, Austria, Croatia, Slovenia and Hungary—according to the criteria of five different geothermal technologies (BHE/DBHE, ATES, BTES, HE, EGS). The Hungarian database contains 177 pre‑qualified, abandoned hydrocarbon wells, only a few of which meet the strict criteria system for geothermal utilization.
Within the project, the Hungarian partners (CROST Regional Development Nonprofit Ltd. in Pécs, Bányavagyon-hasznosító Nonprofit Közhasznú Kft., which also has a site in Baranya County, and the University of Pécs) developed a decision‑support tool and catalog of criteria that enable the uniform and structured evaluation of the wells’ reuse potential. As one of the project’s results, a previously untapped utilization opportunity is now outlined for the town of Biharkeresztes. A feasibility study prepared within the TRANSGEO project draws attention to the fact that the sedimentary rocks forming the Pannonian Basin hide vast geothermal resources. These geothermal reservoirs, located deep within hydrocarbon wells from the 1970s and 1980s that have since fallen into disuse, await rediscovery and utilization. This is not merely a fantasy, as with the right technology and a systematic approach, these wells could become a source of green energy for the city.
The site selection was based on a detailed technical analysis and a structured selection process taking multiple aspects into account. It is not enough for a well to have suitable geological conditions; real success can be achieved only if all parameters of the given site, including technological and market conditions, are in harmony. On the basis of experience, experts developed a strict set of criteria: the ideal well must produce from Upper‑Pannonian formations, its temperature may even be below 50 °C (since heat pumps can extract thermal energy from thermal water even at lower temperatures), and it must have a flow rate of at least 500–700 litres per minute. Integrity is more than a technical concept—the well, which has been dormant for decades, must be undamaged. This, incidentally, must be verified before the well is used for geothermal purposes!
In addition, for geothermal projects that rely on water extracted from an aquifer, it is necessary to have a well nearby where the water used for energy purposes can be reinjected; this ensures the sustainability of the geothermal system and is also required by the regulatory authority. However, the technological and geological conditions only become truly relevant if there is a clearly identifiable local heat market, meaning there are industrial, agricultural, or municipal entities that can use the extracted heat to reduce their own operating costs. Buildings must also meet strict criteria. They must be located close to the well—no more than 3–4 km away to keep infrastructure costs reasonable—and have a substantial heating demand. In addition, a heating system is needed that can operate harmoniously with heat pumps and, where appropriate, can be used in combination with fossil energy sources: the buildings must have a central heating system and the heat‑pump‑based heating can be connected to the existing, typically natural‑gas‑fired boiler heating (bivalent systems).
The geological structure of the Biharkeresztes area meets the requirements. The Ártánd‑2 (Ár‑2) well, drilled in 1975, reached a depth of 2392 metres and revealed a producible quantity of water at the appropriate temperature. Near it, the Biharkeresztes‑31 (Bike‑31) well, drilled in 1988 and reaching a depth of 1950 metres with a similar geological stratigraphy, can be a suitable reinjection well. The Ár‑2 well is a real technical challenge. The well is currently registered as a water well that was converted in the 1970s after the well proved unsuitable for hydrocarbon production. The well is practically vertical and four cement plugs (at 2122, 1900, 1743 and 1016 metres) ensure the isolation of different formations from one another. Above the upper cement plug, a casing section with the appropriate diameter is in place. From the 717–955 metre interval, composed of Upper‑Pannonian sandstones, thermal water can be produced with a flow rate of 700 litres per minute and a surface water temperature of 47 °C, and with special water‑to‑water heat pumps used for energetic utilization a total heating capacity of 1239 kW can be achieved.
Biharkeresztes lies only 20 km from Oradea (Nagyvárad), its area is 49.26 km², and its population is 3921. The feasibility study proposes the inclusion of the town’s central public buildings in the geothermal system, namely schools, kindergartens, the mayor’s office, a medical clinic, the library, and the cultural centre, altogether 11 institutions. These buildings have a nearly continuous heating demand for most of the year. The total annual amount of natural gas used for heating currently stands at approximately 2,889 MWh, which, at current prices, represents an annual energy cost of 126 million forints for the municipality.
The proposed geothermal system was designed with a combined focus on sustainability and cost-effectiveness, as follows. Water at 47 °C is extracted from Well Ár-2 and delivered via insulated piping (3,600 meters in length) to the 11 public buildings. Special water-to-water heat pumps are installed in each building, operating within a temperature range of 42 °C to 25 °C (based on the 47 °C thermal water exiting the well, taking into account heat loss during transport and the temperature-reducing effects of the heat exchangers installed upstream of the heat pumps, hot water with a calculated maximum temperature of 42 °C and a calculated minimum temperature of 25 °C enters the heat pump evaporator) and produce heating water with a supply temperature of 60 °C, which is the temperature required by conventional radiator systems.
Based on the above temperature range and calculated with an average water temperature of 33.5 °C, the seasonal efficiency (SCOP) is 5.9, which means that for every 1 kilowatt-hour of electricity consumed, the heat pumps produce 5.9 kilowatt-hours of thermal energy—naturally, the difference, i.e., the 4.9 kilowatt-hours of thermal energy, is extracted from the thermal water by the heat pumps.
The system was designed to be cost-effective: heat pumps provide all the necessary heat for 95% of the heating season, while gas boilers only come online on the coldest days—accounting for no more than 5% of the heating season—to supplement the heat generated by the heat pumps. This bivalent heating system solution reduces investment costs (since lower-capacity heat pumps are sufficient) and retains the gas boilers as a safety backup. Finally, the cooled thermal water (with a minimum calculated temperature of 21 °C) does not leave the circulation but is reinjected into the well designated Bike-31, ensuring sustainable operation and the preservation of the thermal water supply.
As a result of the planned system, the buildings’ annual natural gas consumption will decrease by 95%, or 2,744 MWh, reducing annual primary energy consumption by 1,949 MWh. The environmental impact of this is also significant, with greenhouse gas emissions decreasing by 603 metric tons of CO₂ equivalent per year. This is equivalent to the annual emissions of approximately 130 cars. If private entities join the project, its implementation will require the establishment of a new district heating company, in which investors, alongside the municipality, can acquire shares. Operations can be carried out with just two part-time technicians.
If Biharkeresztes implements this project, it will not only reduce its own dependence on external energy sources but also set an example for other municipalities to follow. Hungary still has numerous potential hydrocarbon wells, most of which are located in the Great Plain. The methodology and tools developed here can be applied anywhere in the country’s other municipalities.
The feasibility study prepared for the Ártánd‑2 well clearly shows what opportunities the reuse of abandoned deep wells can hold for geothermal energy utilization. Similar potential is also available in Baranya County, since several state‑owned, abandoned deep wells are located in the region, of which the well denoted Szig‑1 appears, on the basis of available data, to be potentially suitable for geothermal energy production. Thermal‑water utilization can offer opportunities especially in agriculture, for example for heating greenhouses and foil tunnels, for drying fruits and vegetables, and for supplying energy for heating and cooling systems of agricultural buildings.
