THE EVIDENCE OF A POTENTIAL GEOTHERMAL RESERVOIR COULD LEAD TO AN ENERGY SAVING OF ABOUT 750 TOE/YEAR.
The northeastern Spanish border is structurally affected by the extensive European rift system of the Mio Pliocene age. The Valles basin, though more than 200 km long, is limited a symmetrically by 2 faults 3000 m and 1000 m deep respectively with granite edges and arcose filling. In 1979 a series of investigations were begun into geothermal prospecting, with the objective of using the potential geothermal resources in the future. The following studies have been carried out in Valles in the period 1979 to 1983: general and detailed geology; determination of the geometry of the graben by means of gravimetry and seismic geophysics; hydrogeological survey of the basin; determination of teh geothermal anomalies by geochemical and geophysical methods such as electrical vertical soundings, simulation pumping (SP), magnetotellurgy (MT), audio MT and seismic noise.

The first test well was drilled in 1983 on 1 of anomalies detected, Sant Cugar. It ended at 400 m and roughly 60 C with a high degree of permeability. The geothermal reservoir consists of a highly fractured granite with excellent secondary permeability due to the present seismic activity in the graben and the hydrothermal alteration. This first drilling has indicated that a low enthalpy geothermal resource in the fractured granite.

The following aspects of the work have been carried out: hydrogeological study of the area of the thermal anomaly of Sant Cugat del Valles (covering geological mapping, climatology, inventory of water sources, surface hydrology, underground hydrology involving extractions and balance):
short duration production test with 4 variations of flow rate (the parameters obtained in this test were load losses in the production well PE-3, transmissivity and storage coefficient);
long duration production test with a constant flow of 80 ls{-1} over 50 days (giving transmissivity, storage coefficient and simulation of the behaviour of the water during an exploitation of 1 year with flow rat es of 30, 50 and 70 ls{- 1} according both to a specific model of simulation pumping barriers (SPB) for this case and to the semiautomatic interpretation of pumping test (ISAPE) model as well);
determination of the bubble point pressure (measurement of the gas/liquid volumetric ratio at atmospheric pressure and measurement of filtration with characterization of particles and bacteriological sampling);
geochemical follow up of the 2 production tests (including variations in the chemical composition of the water produced during both short and long tests and their duration in time).
PUMPING TESTS IN EXISTING BEREHOLES WILL BE CARRIED OUT TO DEFINE A GEOTHERMAL RESERVOIR SITUATED IN THE VALLES GRABEN IN CATALONIA, SPAIN, AND A MARKET STUDY WILL INVESTIGATE THE DEMAND FOR GREENHOUSE OR INDUSTRY HEATING.