163 8. Hydro-stratigraphic study of the Hydrogeological Experimental Site of Poitiers, France The uppermost porous horizon corresponds to bioturbated Bathonian limestones with bivalve assemblages, attributed to the “Assise à silextite” formation (flint band formation). This level covers the “banc à Ctenostreon,” which marks the base of the Bathonian. This level is difficult to interpret using optical imagery, as most boreholes are cased down to 35 m depth. Only boreholes MP4, M17 and M22 reveal a more porous interval around 35 m. The intermediate porous interval, observed between 85 and 87 m depth, corresponds to the first dolomitized interval within the Oolitic Formation. It is characterized by centimetric vugs and coincides with the top of the “Bioclastic and Pelleted Formation,” underlying the D7bis discontinuity. The coalescence of vugs may account for the formation of meter-scale cavities occasionally observed in optical televiewer images. The lowermost porous horizon is associated with the D6 discontinuity and corresponds to the Lower dolomitized zone. For further details about seismic and acoustic methods, refer to Chapter 5 (Mari, 2026). Figure 11 Comparison of acoustic and optical wall imaging methods in borehole M20. From left to right: acoustic section, velocity log, karst index log, geological log, and optical wall imagery (OPTV).
RkJQdWJsaXNoZXIy NjA3NzQ=