## 1 Introduction  
Recently, the role of naturally fractured reservoirs has become increasingly important in numerous fields of applied geology. In this unique type of reservoirs, the complex network of fractures inside a rock body acts exclusively as a space for the migration and storage of lithospheric fluids, such as water and hydrocarbons [1]. Whether or not such a fracture network can transport fluids depends on several factors determined by the tectonic and post-tectonic evolution of the area in question. First, the hydrodynamic behaviour of the network is determined by how the individual fractures are spatially organised (e.g., [2; 3; 4; 5]). The most essential geometric parameters related to this pattern include the density of the fracture system and the orientation and size of the individual fractures. In numerous cases, structural evolution results in mutual connectivity throughout the fracture network, while in other cases, a compartmentalised network may develop, with the fracture system containing sub-systems that do not communicate with each other [6; 7; 8]. In addition to geometrical influences, other factors may also reliably modify the behaviour of the fracture system. For example, certain fractures may close due to increasing lithostatic pressure (depth; [4]). In addition, recent anisotropic stress fieldshave had a significant effect on the opening and closure of fractures with different orientations [4]. In addition to these factors, the conditions of the fractured rock body can be modified by various water-rock interaction processes, such as the dissolution of the host rock and the precipitation of new mineral phases, leading to the formation of mineralised veins.  
In Hungary, the most productive hydrocarbon reservoirs can be found in the Neogene basin-filling sedimentary sequences of the Pannonian Basin [9; 10; 11]. Excellent fractured reservoirs also exist in the pre-Neogene basement, being related to Mesozoic carbonates [12] and Variscan metamorphic rock bodies (e.g., [13]). The hydrodynamic behaviour of these reservoirs differs significantly from that exhibited by typical porous systems. In most cases, impermeable blocks of rocks are separated by highly fractured zones with good reservoir conditions, while elsewhere, rock bodies themselves may contain mutually connected fracture systems. In some localities, the productive intervals communicate with each other, resulting in an entirely connected hydrodynamic system. In addition, there are other basement hydrocarbon fields in the Pannonian Basin in which hydrocarbons of various chemical compositions are produced, suggesting the co-existence of several reservoirs that do not communicate with each other hydrodynamically [14]. In the most extreme situation, 12 wells produce seven types of immiscible oils in a small area on the order of 10 km\({}^{2}\), indicating the existence of a highly compartmentalised fractured basement reservoir [15].  
In this study, we focus on one of the most productive basement hydrocarbon fields in the Pannonian Basin. Over 100 wells penetrate the metamorphic basement in the Szeghalom Dome, most of which produce hydrocarbons [16; 17; 18; 19]. Nevertheless, until now, less than 10% of the total estimated amount has been produced, essentially because of the rather complicated internal structure of the reservoir. The present paper aims to locate possible paleo-migration pathways and the most productive intervals along a single well in the Szeghalom Dome by using a combined approach involving well-log data evaluation, fracture network modelling, and ancient fluid composition analysis.