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True resistivity determination (view source)
Revision as of 20:32, 31 January 2014
, 20:32, 31 January 2014Initial import
{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting reservoir system quality and performance
| frompg = 9-1
| topg = 9-156
| author = Dan J. Hartmann, Edward A. Beaumont
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| 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.
==How invasion affects r<sub>t</sub> measurement==
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.
[[file:predicting-reservoir-system-quality-and-performance_fig9-29.png|thumb|{{figure number|9-29}}See text for explanation.]]
==Obtaining a valid r<sub>t</sub> value==
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>
|-
| <th align="left"> If…</th>
| <th align="left"> Then…</th>
|-
| Bed is
| Correct for this bed using appropriate service company chart
|-
| Shallow, medium, and deep investigating tools measure, different resistivities (i.e., log has step profile)
| Correct for invasion using appropriate service company tornado chart
|}
==See also==
* [[Determining water saturation]]
* [[Calculating Sw from the Archie equation]]
* [[Calculating Rw from SP logs]]
* [[Constructing a Pickett plot]]
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting reservoir system quality and performance]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting reservoir system quality and performance
| frompg = 9-1
| topg = 9-156
| author = Dan J. Hartmann, Edward A. Beaumont
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| 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.
==How invasion affects r<sub>t</sub> measurement==
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.
[[file:predicting-reservoir-system-quality-and-performance_fig9-29.png|thumb|{{figure number|9-29}}See text for explanation.]]
==Obtaining a valid r<sub>t</sub> value==
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>
|-
| <th align="left"> If…</th>
| <th align="left"> Then…</th>
|-
| Bed is
| Correct for this bed using appropriate service company chart
|-
| Shallow, medium, and deep investigating tools measure, different resistivities (i.e., log has step profile)
| Correct for invasion using appropriate service company tornado chart
|}
==See also==
* [[Determining water saturation]]
* [[Calculating Sw from the Archie equation]]
* [[Calculating Rw from SP logs]]
* [[Constructing a Pickett plot]]
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting reservoir system quality and performance]]