The Evaluation of Complex Borehole Geophysics and Corescanning: for Detailed Characterization of Oriented Fracture Sets, Zones, and Hydraulic Flow on Different Scales. A Case Study: Moragy Granite, Mecsek Mts., Hungary

Our presentation outlines the methodology to determine the relationship between fractures and flow systems, and it tries to homogenize the results deriving from methods of different resolutions in a geological model. The granite suffered multi-phase brittle deformation during the Alpine orogene, the fractures renewed several times and were filled with multi-generation infillings. The cores were scanned with the ImaGeo system, the fractures were oriented, characterized in detail from geological and geophysical point of views, and structurally evaluated. A structural model was sketched (Maros et al 2004). The results were refined by the information received from geophysical data, primarily from well-logging (Zilahi-Sebess et al 2003), but radar measurements, crosshole velocity tomography were also used (Toros et al 2004). Transmissivity in granite: 10-6-10-12, main fractures: 10-6-10-5 m2/s. Porous and fracture flow models were set up (Benedek et al 2003, Balla et al 2004). Correlations were found between the core-logging and the well-logging: acoustic openness, density, acoustic velocity, resistivity versus fracture frequency, fracture zones versus HPF influx places. The complex evaluation made the determination of the size and dip of fracture zones more precise. The flow characteristics of individual fractures and fracture zones, however, are influenced by their unique features; no parameter-group can be selected that definitely produces permeable or impermeable fractures. The interpretation of the observations carried out on different scales can be done in several ways. One method is to use methods of different resolutions densely enough to be representative. We examined the relation of information deriving from high resolution methods and the well-logging. On the basis of the depth-trends it is possible to extrapolate the information around the borehole. The relationship with the geophysical surveys is possible through the resistivity and acoustic measurements. An important agent is the VSP, which provides a direct comparison between the surface and the well-logging measurements. Another method is the scaling of the fractal distribution of fractures, since, apparently, the permeability on core-scale can be deduced from the large-scale tectonics. But the uncertainty of this cannot be predicted due to the numerous infilling events. Besides, the same infilling event acts differently on different scales. Similarly, the permeability of the blocks cannot be deduced from the porosity of the cores, because the fracture system is pressure-sensitive due to the unevenness of the fracture surfaces, and is also influenced by the mineralization and the ion concentration of the water. So core examinations, permeability measurements (BHTV, HPF), and their comparison to hydrodynamic testing are essential. Balla, Z. et al 2004: Hydrogeological pattern of the Bataapati Site - Ann. Rep. of the Geol. Inst. of Hung. pp. 449-472. Benedek, K. et al 2003: Hydrodynamical modelling for safety assessment - Manuscript, Batatom kft, Hungary Maros, Gy. et al 2004: Tectonics and structural evolution of the NE part of the Moragy Hills - Ann. Rep. of the Geol. Inst. of Hung. pp. 371-401. Toros, E. et al 2004: Complementary ground-based and borehole seismic and radar survey at the Bataapati site - Ann. Rep. of the Geol. Inst. of Hung. pp. 265-284. Zilahi-Sebess, L 2003: Well-logging methods to investigate a granitic site for radioactive waste deposition,- Geoph. Trans. 44/ 2. pp. 51-93.