PHYSICAL ROCK PROPERTIES OF THE BOREHOLE EYREVILLE — MEASUREMENTS AND PRELIMINARY INTERPRETATION

The projects aims to contribute to the physical characterization of the cored lithology in the borehole Eyreville and a better understanding of correlation between petrophysical properties and the mineralogical composition as well as the texture, and by this the possible influence of the impact on the petrophysical properties.

Approx. 330 samples with equidistant sampling, covering the complete cored depth interval (127-1765 m) were chosen for the determination of thermal parameters, density and porosity (cf. Popov et al. this session). On a representative subgroup of samples ultrasonic P- and S-wave velocity was measured. For mechanically stable samples (all granites and some selected suevites, breccia, schists and pegmatites) the measurements were performed under dry and fully saturated conditions considering pressure dependence. For mechanically unstable sandstone samples the velocities under fully saturated conditions will be estimated using measurements on dry and wet samples by physical modeling.

P-wave velocities in high porosity (27% - 67%) sediments above 1100m lie between 1.2 and 2.8 km/s (dry rocks). In the granite megablock section P-velocities between 5.8 and 6.5 km/s are found (saturated rocks), typical for low porosity granite. For these rocks the physical properties reflect the varying mineralogical content. The velocity is also influenced by texture (e.g. micro-cracks). In the suevite - lithic breccia section and the shist – pegmatite section the P-velocities are significantly lower (2.8 - 5.8 km/s) whereas density of solid material is partly higher than in the granites due to different mineral content. The velocity values can be explained by both, higher porosity (up to 22 %) and higher amount of micro-cracks in the rocks.

The internal surface measured by BET reflects the different type of rocks with different micro-morphology. Internal surface of clay is significantly higher than that of sandstone due to lamelar structure of clay minerals. Internal surface of granite is in general lower than of rocks of the suevite and the schist - pegmatite section. The differences will be further investigated by analysis of SEM-images. Hydraulic bulk permeability will be estimated with various physical models using internal surface for the different rock types.