COMPARATIVE-ANALYSIS OF DIRECT (CORE) AND INDIRECT (BOREHOLE IMAGING TOOLS) COLLECTION OF FRACTURE DATA IN THE HOT-DRY-ROCK-SOULTZ-RESERVOIR (FRANCE)

Attributes of several thousand fractures were collected in three boreh oles of 2.2, 3.6, and 3.8 km depth, penetrating the Soultz Hot Dry Roc k reservoir(France). The fractures were sampled from cores and from se veral high-resolution imaging techniques such as borehole televiewer ( BHTV), ultrasonic borehole imager (UBI), formation microscanner (FMS), formation microimager (FMI), and azimuthal resistivity imaging(ARI). A comparison was made between the data collected on cores and those pr ovided by different imaging techniques. The comparison clearly establi shes that the different wall- images are not as exhaustive as the core data and cannot provide a complete characterization of the fracture n etwork. Discrete fractures thinner than 1 mm are not properly detected . This is also the case for discrete fractures closer than 5 mm, which appear only as single traces. The imaging techniques are, nevertheles s, very powerful for characterizing altered fracture clusters. Whateve r the technique used, the fracture strikes were correctly sampled with the different systems. This comparison allowed us to calibrate the fr acture population data obtained from the imaging system in order to co rrect for the filtering effect introduced by the technique itself and by the alteration of the rock mass.