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Line 178: − Note that an equivalent “quick look” solution can be obtained by an overlay technique using logarithmically scaled ''R''<sub>t</sub> and ''R''<sub>xo</sub> logs. If one log is placed over the other and shifted so that the two curves coincide in clean, water-bearing zones, the 1 ohm-m line on the ''R''<sub>xo</sub> log grid will lie on the ''R''<sub>t</sub> grid at a value equal to ''R''<sub>w</sub>/''R''<sub>mf</sub>. Since ''R''<sub>mf</sub> is known, ''R''<sub>w</sub> can then be easily calculated. Figure 4 shows an example of original and shifted logs indicating a ''R''<sub>t</sub>/''R''<sub>mf</sub> ratio of 0.45.+ − − − +
Water resistivity determination (view source)
Revision as of 22:17, 20 January 2014
, 22:17, 20 January 2014→Resistivity ratio method
==Resistivity ratio method==
==Resistivity ratio method==
[[file:determination-of-water-resistivity_fig3.png|left|thumb|{{figure number|3}}Log used in example of calculation of water resistivity. Copyright: the SP method. (From <ref name=pt04r20>Western Atlas International, 1985, Atlas log interpretation charts: Houston, TX.</ref>; courtesy of Atlas Wireline Division of Western Atlas.]]
===Principle===
===Principle===
* Calculate ''R''<sub>w</sub> from Equation 8.
* Calculate ''R''<sub>w</sub> from Equation 8.
[[file:determination-of-water-resistivity_fig4.png|thumb|{{figure number|4}}Example problem showing determination of ''R''<sub>w</sub> from resistivity ratio.]]
[[file:determination-of-water-resistivity_fig3.png|thumb|{{figure number|3}}Log used in example of calculation of water resistivity. Copyright: the SP method. (From <ref name=pt04r20>Western Atlas International, 1985, Atlas log interpretation charts: Houston, TX.</ref>; courtesy of Atlas Wireline Division of Western Atlas.]]
[[file:determination-of-water-resistivity_fig4.png|thumb|{{figure number|4}}Example problem showing determination of ''R''<sub>w</sub> from resistivity ratio.]]
Note that an equivalent “quick look” solution can be obtained by an overlay technique using logarithmically scaled ''R''<sub>t</sub> and ''R''<sub>xo</sub> logs. If one log is placed over the other and shifted so that the two curves coincide in clean, water-bearing zones, the 1 ohm-m line on the ''R''<sub>xo</sub> log grid will lie on the ''R''<sub>t</sub> grid at a value equal to ''R''<sub>w</sub>/''R''<sub>mf</sub>. Since ''R''<sub>mf</sub> is known, ''R''<sub>w</sub> can then be easily calculated. [[:file:determination-of-water-resistivity_fig4.png|Figure 4]] shows an example of original and shifted logs indicating a ''R''<sub>t</sub>/''R''<sub>mf</sub> ratio of 0.45.
===Limitations===
===Limitations===