HYDROLOGICAL ASPECTS OF GEOPHYSICAL BOREHOLE MEASUREMENTS IN CRYSTALLINE ROCKS OF THE BLACK-FOREST

One of six wells drilled into the crystalline rock of the Black Forest basement during the German Continental Deep Drilling Project (KTB) si te survey has been used to detect hydraulically active fractures and t o identify their character by a variety of logging tools such as calip er and televiewer logging, vertical seismic profiling (VSP) and electr ical and thermal measurements in addition to standard logging recordin gs. In the 265 m Moosengrund well drilled into the Triberg granite bod y these methods were applied successfully to discriminate between frac tures and breakouts and to identify open and closed fractures and wate r-consuming or water-expelling fractures, respectively. Fracture strik e, dip and width were determined from televiewer data. VSP measurement s were used to determine the seismic velocities in the unfractured roc k and the fracture zones. Estimates of permeability (10-55 Darcy) and transmissivity (0.1-1.0 cm2 s-1) of the fracture zones were obtained b y the analysis of P waves and tube waves in the VSP records. The summe d values of the transmissivity yield an upper estimate of the overall transmissivity determined by a pumping test.