Converting Abandoned Hungarian Oil and Gas Wells Into Geothermal Sources

Abstract

Hungary’s excellent geothermal potential is well-known. Based on the Geothermal Atlas of Hungary, published in 2016, 1622 thermal wells produce hot water for direct heat utilization. In addition, it was shown that many abandoned oil and gas wells were good possible sources for geothermal energy production. This paper investigates the suitability of abandoned wells in Hungary for possible hydrothermal or Enhanced Geothermal Systems (EGS) applications. The study identifies 70 of the abandoned wells, characterized by medium to high terrestrial heat flows (75-100 mW/m2), located for the most part in sedimentary layers and having to a lesser extent fractured geology. At a depth of 1000 m, the bottom hole temperatures are 40 to 69 C. These rock temperatures are sufficient for low-temperature direct use such as district heating, greenhouse heating, and aqua-culture, all using either hydrothermal or EGS systems. The mitigation of drilling costs and the documented lithology can obviously and significantly reduce the risk associated with EGS. The feasibility of using these wells as deep BHE applications within abandoned hydrocarbon wells is demonstrated here with analytical and numerical models.