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  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

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Water resistivity or R_w, is a critical component of log analysis in calculating water saturation using the Archie equation. R_w can be measured from a sample of formation water taken from the zone of interest at the well site or a nearby well, or it can be calculated using spontaneous potential (SP) log data.

Water resistivity or R_w, is a critical component of log analysis in calculating [[water saturation]] using the Archie equation. R_w can be measured from a sample of formation water taken from the zone of interest at the well site or a nearby well, or it can be calculated using spontaneous potential (SP) log data.

==Data required==

==Data required==

==Converting r_m to r_mf==

==Converting r_m to r_mf==

[[file:predicting-reservoir-system-quality-and-performance_fig9-32.png|thumb|{{figure number|1}}. Copyright: Schlumberger.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-32.png|thumb|{{figure number|1}} Copyright: Schlumberger.]]

If the log header gives R_m only, then R_m must be converted to R_mf using this procedure:

If the log header gives R_m only, then R_m must be converted to R_mf using this procedure:

==Step 2: convert r_mf to r_mf at formation temperature==

==Step 2: convert r_mf to r_mf at formation temperature==

[[file:predicting-reservoir-system-quality-and-performance_fig9-33.png|thumb|{{figure number|2}}. Copyright: Schlumberger.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-33.png|thumb|{{figure number|2}} Copyright: Schlumberger.]]

Follow this procedure to convert R_mf (measured at surface temperature) to R_mf at formation temperature.

Follow this procedure to convert R_mf (measured at surface temperature) to R_mf at formation temperature.

==Step 3: convert r_mf to r_{mf eq}==

==Step 3: convert r_mf to r_{mf eq}==

[[file:predicting-reservoir-system-quality-and-performance_fig9-34.png|thumb|{{figure number|3}}. Copyright: Schlumberger.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-34.png|thumb|{{figure number|3}} Copyright: Schlumberger.]]

Use the R_mf at formation temperature obtained above and follow the procedure below to convert R_mf to equivalent mud filtrate resistivity (R_mf _eq).

Use the R_mf at formation temperature obtained above and follow the procedure below to convert R_mf to equivalent mud filtrate resistivity (R_mf _eq).

==Step 4: convert SP to r_we==

==Step 4: convert SP to r_we==

[[file:predicting-reservoir-system-quality-and-performance_fig9-35.png|thumb|{{figure number|4}}. Copyright: Schlumberger.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-35.png|thumb|{{figure number|4}} Copyright: Schlumberger.]]

Follow the procedure below to convert SP from the zone of interest to equivalent formation water resistivity (R_we).

Follow the procedure below to convert SP from the zone of interest to equivalent formation water resistivity (R_we).