123 5. Contribution of seismic and acoustic methods to the characterization of karstic formations heterogeneity of the aquifer reservoir in the horizontal and vertical planes. To quantify the porosity variations within this aquifer, the seismic interval velocities were first converted into resistivity values. For this purpose, the empirical relationship between seismic velocity and resistivity proposed by Faust [10] was used. Resistivity values were then converted into porosity values, using Archie’s law [11]. Figure 5.3 (bottom) shows the pseudo velocity and porosity seismic sections for the in-line 21 and cross-line 24. The resulting 3D seismic pseudo-porosity block revealed three high-porosity layers, at depths of 35 to 40 m, 85 to 87 m and 110 to 115 m. The 85 to 87 m layer is the most porous, with porosities higher than 30 %, which represents the karstic part of the reservoir. Figure 5.4 shows the distributions of porous bodies in the 80 to 90 m and 100 to 120 m depth intervals. Figure 5.4 Distribution of karstic bodies. Top: in the 80 to 90 m depth interval. Bottom: in the 100 to 120 m depth interval.
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