Geological risk analysis of geothermal developments in a sedimentary basin, Hungary

In our research, we develop a novel methodology to evaluate the geological uncertainties of geothermal exploration in order to quantify them. The outcomes can be used as inputs when deciding on new geothermal investments. Adapted from the hydrocarbon industry probability of success is evaluated by estimating potential geological risk factors which can hinder geothermal production and reinjection, following the risk assessment scheme of petroleum play analysis. As a case study in a clastic geological environment, we test the methodology on the Zala Basin, a sedimentary subbasin of the Pannonian Basin, Hungary. Here, the Neogene (so-called Pannonian) sediments form one of the principal thermal water-reservoirs. Although the preliminary geothermal potential of the Zala region (SW Hungary) is assessed to be good, there is a need for more thorough analysis before starting new developments. As an example, heterogeneity of the deltaic and fluvial deposits poses geological risk. In our case study, we consider the risk of insufficient temperature, the absence of the appropriate aquifer formations, the bad quality of the aquifer i.e., the unfavourable distribution of the high permeable sandstone bodies, the insufficient permeability and flow rate as well as the potential risk of unsuccessful reinjection. This is done by combining and evaluating datasets from well data (lithology, well logs, well tests) and 3D seismic measurements. The goal of the assessment is to decide whether a future geothermal system can provide sufficient capacity, in the current case, for industrial or agricultural heat utilisation. The first author was supported, and the research was financed through the KDP-2021 Cooperative Doctoral Programme of the Ministry of Innovation and Technology (Hungary) from the source of the National Research, Development and Innovation Fund, grant number: KDP_2021_ELTE_C1789026. The study was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21- 2022-00014 project.