f Convective heat transfer at the Soultz geothermal site - Implication to oil potentialities

The Soultz-sous-Forêts, situated at the western limit of the upper Rhine Graben (Eastern France), has been selected by the European Hot Dry Rock (HDR) geothermal project as a pilot zone for exploiting low enthalpy energy. The northwestern part of the Rhinegraben is characterized by an asymmetric sedimentary cover (1400m compared to 3500m on the eastern part), a granitic fractured bed rock and a high surface heat flow (up to 150mW m-² on the western part compared to 70-80mW m-² on the east). The temperature gradient encountered during drilling decreased from values of 0.04 - 0.08 °C m-¹, in the sediment to an unexpectedly low value of 0.01-0.02 °Cm-¹ in the granitic bedrock at depths of 1700-2000m. Horizontal and vertical thermal conductivities of 13 rocks, sampled regularly from depths of 1400 to 2200m along the EPS 1 drill hole, show that the granitic basement at Soultz is homogeneous and isotropic with a mean values of 2.88 ± 0.17 w.m-¹ .K-¹ at 25°C and 2.5 ± 0.15 w.m-¹ .K-¹ at in situ temperatures.