Environmental Engineering Reference
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attributed the phenomenon to the presence of metallic mineralization, but
claimed that background effects often masked metallic mineral PP (IP)
anomalies, to the extent that they were difficult to identify. Later studies
identified the source of these anomalies as due to Membrane Polarization
in clay mineral sand mixtures (Hill, 1999; Komarov and Shmarova, 1961;
Mayper, 1959a & 1959b; and Sumner, 1976). Faced with the polarization pro-
voquee signal/noise problem, Conrad Schlumberger concentrated on using
surface equal potential and resistivity mapping to locate ore bodies and later
gravitated to making wireline measurements in oil wells, co-founding the
oilfield services firm, Schlumberger, which bears the family name.
3.6.1
Mesoscopic Polarization Model
If one imagines that the subsurface rocks can be thought to host a meso-
scopic (i.e., pore scale and larger) distribution of polarization sites, then in
the absence of an electrical field, these polarization sites remain unpolar-
ized (see figure 3.5). In the presence of an electric field, however, these sites
become polarized over time, as shown in figure 3.6, resulting in a volume
polarization field, in opposition to the electrical field. If the electrical field
is removed, the polarization sites gradually decay, resulting in a current in
opposition to the charging current. This discussion, as well as figures 3.5
and 3.6, provide a qualitative explanation of the observations, shown sche-
matically, in figures 3.3 and 3.4.
Note: The current discussion and the schematic models of figures 3.5
and 3.6 are mechanism independent.
Figure 3.5 Schematic representation of polarizable rock/soil as a mesoscopic distribution
of unpolarized polarization sites (after Hill, 1999)
 
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