The Use of Outcrops on the Catalonian Coastal Ranges as Analogue for Deep Geothermal Reservoir Characterization in the Upper Rhine Graben

Abstract

Graben structures are extensively prospected as high enthalpy geothermal targets. The West European rift system started during the Oligocene and stopped their extension during the Miocene. In this graben, the existence of a particularly high thermal gradient spots allow to consider the opportunity to the development of different deep geothermal energy exploitation projects. These projects aim to exploit the graben basement and the interface with their overlapping sediments. Due to the poor matrix permeability of these rocks, the fluid flow in theses reservoirs is mainly controlled by the natural fracture and fault network and associated weathered materials. Unconfortunately, the fracture and fault pattern at reservoir scale in the basement is not well known and is difficult to characterize with the actual geophysical tools. The use of analog rocks at the outcrop is therefore an important tool for helping the reservoir characterization. This study presents a multiscale analysis of the basement outcropping on the Catalonian Coastal Ranges that outcrops at the shoulder of the West European rift in NE of Spain. The first step was to combine satellite pictures, field studies and laboratory measurement in order to define the fault, fracture and cracks network at the largest range of scales as possible with the characterization of structures parameters (lenghts, orientations…). That have lead us to construct a reservoir’s model composed by blocks of different orders depending on their size bounded themselves by faults with decreasing thickness and lengths. Blocks and faults are dressed with their reservoir or matrix porosity. The second step was to compare these geometrical properties acquired on outcrops with data from the well know Soultz-sous-Forêt EGS site and to help the understanding of flow circulation in the basement reservoir on the site and more generally in graben context.