Geomechanical properties of the Meletta sandstone - the high-temperature heat storage reservoir rock of DeepStor

The DeepStor project aims at storing excess heat at temperatures up to 140 ◦C in the depleted Leopoldshafen oil
field at a depth of about 1300 m. In order to gain knowledge on the target horizons, the different layers of the
Meletta sandstone, samples cored in a block retrieved in a quarry near Nussloch where the Meletta sandstone
outcrops were studied. Several petrophysical properties were investigated including mineralogy, porosity,
permeability, thermal conductivity, P- and S-wave velocities and quality factor. A mechanical study focused on
compressive strength under uniaxial and triaxial stress conditions, tensile strength, critical pressure and stress-
dependence of physical properties. Our results show that the Meletta sandstone is heterogeneous, anisotropic,
mechanically weak, stress-sensitive and prone to water weakening. Petrophysical measurements on few Meletta
sandstone cores retrieved in boreholes at about 1250 m depth showed that the outcrop samples are significantly
less cohesive and weaker. Therefore, one should consider the Nussloch outcrop as a good reservoir analog only
with great caution. Several models were applied to account for our experimental results on anisotropy, me-
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chanical behavior and stress-dependence of the outcrop samples. Our study provides a valuable data set which
can feed numerical models to simulate the behavior of the host formation during heat exchange operations in the
DeepStor project.