Model review and sensitivity analysis of the Sárospatak reservoir model, NE-Hungary

Abstract

Hungary’s favourable natural conditions for geothermal energy production and utilization are well known. The anomalously high thermal gradient and the significant expanse of deep aquifers make Hungary one of the most notable European countries regarding low-temperature geothermal resources. Among other cities, Sárospatak in northeast Hungary has utilized its deep carbonate geothermal reservoir for bathing purposes since the 1960s. In recent years, a 7-layer, threedimensional numerical model with two proposed wells for district heating was constructed by the Icelandic company Vatnaskil Consulting Engineers. The main objective was to predict the impact of the planned well duplet on the geothermal reservoir at Sárospatak with a special focus on the existing geothermal wells associated with the thermal spa of the city. In this study, after a model and literature review, a detailed sensitivity analysis with 11 different scenarios was performed. Results of the analysis show that 1) the model is not sensitive to input parameters in its lower layers, 2) the model is not sensitive to the porosity and 3) the model is very sensitive to the hydraulic conductivity in the top model layers, especially the producing layer. It has also been shown that the proposed wells are not likely to have any negative impact on the existing thermal wells. On the other hand, the study shows that the existing thermal wells could have a significant impact on the reservoir pressure at the proposed well duplet. Lack of data related to the existing thermal wells (their actual production and the exact thickness and extent of the tuff layer from which they are producing) are crucial factors preventing their actual impacts from being known. These impacts could be the key in determining the success of the Sárospatak geothermal project.