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Line 14: − + − During the drilling process, filtrate water from the drilling fluid invades the formation. Its resistivity (R<sub>mf</sub>) is either greater than, less than, or equal to R<sub>t</sub> and can distort deep resistivities. Distortions to resistivities due to invasion must be corrected to get a valid R<sub>t</sub> value. The diagram below shows resistivity profiles of formations with fresh and saltwater mud filtrate invasion. − + + + − Use the table below to obtain an uninvaded zone resistivity (R<sub>t</sub>).+ − − {| class = "wikitable" − |- − ! Step − ! Action − |- − | 1 − | Read the resistivity of the log with deepest investigation (ILD, LLD, etc.). − |- − | 2 − | Use the table below to determine how to make corrections. − − * <table-wrap id="ch09utbl21a" position="float"> <table frame="hsides"> <colgroup> <col align="left"></col> <col align="left"></col> </colgroup> <thead> <tr> <th align="left"> If… </th> <th align="left"> Then… </th> </tr> </thead> <tbody> <tr> <td align="left"> Bed is Correct for this bed using appropriate service company chart </td></tr> <tr> Shallow, medium, and deep investigating tools measure, different resistivities (i.e., log has step profile) Correct for invasion using appropriate service company tornado chart </tr> </tbody> </table> </table-wrap> + + + − + − − + − − + − − + − + + Line 61:
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True resistivity determination (view source)
Revision as of 16:16, 5 April 2022
, 16:16, 5 April 2022added Category:Treatise Handbook 3 using HotCat
| part = Predicting the occurrence of oil and gas traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting reservoir system quality and performance
| chapter = Predicting reservoir system quality and performance
| frompg = 9-1
| frompg = 9-48
| topg = 9-156
| topg = 9-48
| author = Dan J. Hartmann, Edward A. Beaumont
| author = Dan J. Hartmann, Edward A. Beaumont
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| isbn = 0-89181-602-X
| isbn = 0-89181-602-X
}}
}}
The true resistivity (R<sub>t</sub>) of a formation is its resistivity when not contaminated by [[drilling fluid]]s. It may contain formation water only (S<sub>w</sub> = 100%) or formation water and hydrocarbons (S<sub>w</sub> t is fundamental when analyzing well logs for the presence of hydrocarbons. For a discussion of resistivity concepts see Asquith, 1982.
The true resistivity (R<sub>t</sub>) of a formation is its resistivity when not contaminated by [[drilling fluid]]s. It may contain formation water only ([[water saturation]] [S<sub>w</sub>] = 100%) or [[formation water]] and hydrocarbons (S<sub>w</sub> < 100%). Using a valid R<sub>t</sub> is fundamental when analyzing well logs for the presence of hydrocarbons. For a discussion of resistivity concepts see Asquith, 1982.
==How invasion affects r<sub>t</sub> measurement==
==How invasion affects r<sub>t</sub> measurement==
[[file:predicting-reservoir-system-quality-and-performance_fig9-29.png|thumb|{{figure number|9-29}}See text for explanation.]]
[[file:predicting-reservoir-system-quality-and-performance_fig9-29.png|500px|thumb|{{figure number|1}}Resistivity profiles of formations with fresh and saltwater mud filtrate invasion.]]
During the drilling process, filtrate water from the drilling fluid invades the formation. Its [[Resistivity of mud filtrate|resistivity (R<sub>mf</sub>)]] is either greater than, less than, or equal to R<sub>t</sub> and can distort deep resistivities. Distortions to resistivities due to invasion must be corrected to get a valid R<sub>t</sub> value. The diagram in [[:file:predicting-reservoir-system-quality-and-performance_fig9-29.png|Figure 1]] shows resistivity profiles of formations with fresh and saltwater mud filtrate invasion.
==Obtaining a valid r<sub>t</sub> value==
==Obtaining a valid r<sub>t</sub> value==
To obtain an uninvaded zone resistivity (R<sub>t</sub>)
# Read the [[Basic_open_hole_tools#Resistivity|resistivity]] of the log with deepest investigation (deep induction log [ILD], deep laterolog [LLD], etc.).
#Use the table below to determine how to make corrections.
{| class="wikitable"
|-
|-
| <th align="left"> If…</th>
! If… || Then…
| <th align="left"> Then…</th>
|-
|-
| Bed is
| Bed is < 20 ft thick for an [[Basic open hole tools#Induction|induction log]] or < 4 ft thick for a [[Basic open hole tools#Laterologs|laterolog]] || Correct for this bed using appropriate service company chart
| Correct for this bed using appropriate service company chart
|-
|-
| Shallow, medium, and deep investigating tools measure, different resistivities (i.e., log has step profile)
| Shallow, medium, and deep investigating tools measure different resistivities (i.e., log has step profile) || Correct for invasion using appropriate service company tornado chart
| Correct for invasion using appropriate service company tornado chart
|}
|}
==See also==
==See also==
* [[Determining water saturation]]
* [[Determining water saturation]]
* [[Calculating Sw from the Archie equation]]
* [[Archie equation]]
* [[Calculating Rw from SP logs]]
* [[Calculating Rw from SP logs]]
* [[Constructing a Pickett plot]]
* [[Pickett plot construction]]
* [[Basic open hole tools]]
==External links==
==External links==
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting reservoir system quality and performance]]
[[Category:Predicting reservoir system quality and performance]]
[[Category:Treatise Handbook 3]]