Specifications

University of Pretoria etd – Combrinck, M (2006)
assumption made in this method that cumulative conductance will always increase with
increasing depth and the standard algorithm only calculates the derivatives for points until
the depths start decreasing. For this specific case the slope of the curve was calculated in
an alternate manner to investigate the conductivity behaviour.
The negative “conductivity” values and dramatic overshoot of the last positive slopes
(Figure 4-28) show no relation to the true conductivities and does not add much value to
the process. At first sight this might seem as a failure of the S-layer method, but the very
distinctive pattern can easily be recognised on the cumulative conductance curves and will
indicate the existence of a very conductive layer. The exact position of the boundary is not
well defined, but can best be described from the conductivity curves as the first rise in
conductivity. This transition is easier distinguished on graphs with linear scale (Figure 4-
30).
1
10
100
0 50 100 150 200 250 300 350
Depth [m]
Cumulative Conductance [S]
Two Layers: Layer 1, 0.02 S/m, 200 m;
Layer 2, 0.2 S/m
Two Layers: Layer 1, 0.02 S/m, 200 m;
Layer 2, 2 S/m
Figure 4-28: Cumulative conductance versus depth for two layers of increasing conductivity;
first layer thickness 200m.
72