Elaboration of Multi-Scale Fluid Flow Modeling System in Fractured Rocks for Exploitation of Geothermal Energy

Abstract

The Pannonian Basin of Hungary represents one of the areas of highest geothermal energy potential in Europe. The basin is a deep Neogene depression, surrounded by the Carpathian mountains, filled by more than 6000 m of Miocene – Pliocene sediments. These are underlain by pre-Neogene metamorphic crystalline basement rocks of granitoid composition.

In order to efficiently and sustainably exploit this geothermal resource, both water and heat balances need to be fully understood. One component of this understanding is a knowledge of the geothermal fluid (i.e. hot groundwater) flow regime in the fracture systems of the underlying basement. This, in turn, requires information on the tectonic framework that has shaped these fracture systems and controls their permeability distribution. Unfortunately, direct study of the crystalline basement (beneath 6000 m of sediments) is impractical and glimpses of the basement can only be caught in deep exploration boreholes.

However, in other parts of the world, similarly fractured bedrock aquifers, shaped by analogous extensional tectonic regimes, can be observed in the shallow subsurface. In particular, study of the rocks of the Oslo palaeograben (Norway) offer insight into the fracture systems likely to be found in the sub-Pannonian basement. Fortunately, the granitoid basement rocks of south-east Norway are found at the surface, exposed by glacial activity and post-Tertiary erosion, and may be examined in detail and used an analogue for understanding of deep rocks.