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Line 23: + + + − {| class = "wikitable"+ − |-+ − ! Step+ − ! Action − |- − | 1 − | Find the purest shale intervals on the GR or SP base line. They must be reasonably thick to allow valid responses of the other logs and free of sand or lime stringers. (See points a–e, [[:file:formation-fluid-pressure-and-its-application_fig5-20.png|Figure 1]].) − |- − | 2 − | At the same depth, mark the value of resistivity, conductivity, sonic travel time, or density. − |- − | 3 − | Note any series of these best shale values vs. depth. These define a normal shale trend (NST) line for each of the log curves to be used. − |} − − [[file:formation-fluid-pressure-and-its-application_fig5-20.png|thumb|{{figure number|1}}An illustration of how overpressures are interpreted from different types of well logs.]] Line 48:
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Pressure prediction: analysis of well-log and seismic data (view source)
Revision as of 17:57, 17 February 2022
, 17:57, 17 February 2022added Category:Treatise Handbook 3 using HotCat
{{Merge|Pressure prediction}}
{{publication
{{publication
| image = exploring-for-oil-and-gas-traps.png
| image = exploring-for-oil-and-gas-traps.png
| part = Critical elements of the petroleum system
| part = Critical elements of the petroleum system
| chapter = Formation fluid pressure and its application
| chapter = Formation fluid pressure and its application
| frompg = 5-1
| frompg = 5-41
| topg = 5-64
| topg = 5-43
| author = Edward A. Beaumont, Forrest Fiedler
| author = Edward A. Beaumont, Forrest Fiedler
| link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm
| link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm
==Procedure: analyzing well logs==
==Procedure: analyzing well logs==
[[file:formation-fluid-pressure-and-its-application_fig5-20.png|thumb|300px|{{figure number|1}}How overpressures are interpreted from different types of well logs.]]
To locate intervals with potentially abnormal fluid pressure, use the following procedure.
To locate intervals with potentially abnormal fluid pressure, use the following procedure.
# Find the purest shale intervals on the GR or SP base line. They must be reasonably thick to allow valid responses of the other logs and free of sand or lime stringers. (See points a–e, [[:file:formation-fluid-pressure-and-its-application_fig5-20.png|Figure 1]].)
# At the same depth, mark the value of resistivity, conductivity, sonic travel time, or density.
# Note any series of these best shale values vs. depth. These define a normal shale trend (NST) line for each of the log curves to be used.<br>
''' Note: ''' Departure from the NST line indicates abnormal microporosity due to abnormal pore pressure.
''' Note: ''' Departure from the NST line indicates abnormal microporosity due to abnormal pore pressure.
==Diagram of log response to overpressure==
==Diagram of log response to overpressure==
[[:file:formation-fluid-pressure-and-its-application_fig5-20.png|Figure 1]] illustrates how overpressures are interpreted from different types of well logs, as explained in the previous table.
[[:file:formation-fluid-pressure-and-its-application_fig5-20.png|Figure 1]] illustrates how overpressures are interpreted from different types of well logs, as explained in the previous table.
==Travel time from sonic logs==
==Travel time from sonic logs==
[[file:formation-fluid-pressure-and-its-application_fig5-21.png|thumb|{{figure number|2}}Sonic travel time varies with measured pressure. Copyright: Powley, 1990; courtesy Earth Science Reviews.]]
[[file:formation-fluid-pressure-and-its-application_fig5-21.png|thumb|300px|{{figure number|2}}Sonic travel time varies with measured pressure. From Powley;<ref name=ch05r14>Powley, D. E., 1990, Pressures and hydrogeology in petroleum basins: Earth Science Reviews, vol. 29, p. 215–226.</ref> courtesy Earth Science Reviews.]]
In some places, an empirical relation can be established to predict pore pressure from well logs. [[:file:formation-fluid-pressure-and-its-application_fig5-21.png|Figure 2]] shows sonic travel time varying with measured pressure.
In some places, an empirical relation can be established to predict pore pressure from well logs. [[:file:formation-fluid-pressure-and-its-application_fig5-21.png|Figure 2]] shows sonic travel time varying with measured pressure.
==[[Synthetic seismogram]]s==
==Synthetic seismograms==
Resistivity, sonic, and density logs can be used to construct [[synthetic seismogram]]s which, in turn, can be used to calibrate and refine seismic profiles. Hence, there is a tie-in with geophysical [[modeling]] (directly in the case of sonic–density transforms, indirectly in the case of resistivity transforms).
Resistivity, sonic, and density logs can be used to construct [[synthetic seismogram]]s which, in turn, can be used to calibrate and refine seismic profiles. Hence, there is a tie-in with geophysical [[modeling]] (directly in the case of sonic–density transforms, indirectly in the case of resistivity transforms).
{| class = "wikitable"
{| class = "wikitable"
|-
|-
! Log type
! Log type || Overpressure || Underpressure
|-
|-
| Drilling rate
| Drilling rate || Faster || Slower
| Faster
| Slower
|-
|-
| SP
| SP || May shift to negative || May shift to positive
| May shift to negative
| May shift to positive
|-
|-
| Gamma ray
| Gamma ray || May decrease slightly || May increase slightly
| May decrease slightly
| May increase slightly
|-
|-
| Resistivity
| Resistivity || Lower || Higher
| Lower
| Higher
|-
|-
| Conductivity
| Conductivity || Higher || Lower
| Higher
| Lower
|-
|-
| Density
| Density || Lower || Higher
| Lower
| Higher
|-
|-
| Travel time
| Travel time || Slower || Faster
| Slower
| Faster
|-
|-
| Seismic interval velocity
| Seismic interval velocity || Low || High
| Low
| High
|}
|}
==See also==
==See also==
* [[Predicting abnormal pressures]]
* [[Abnormal pressure prediction]]
* [[Reconstructing burial history]]
* [[Pressure prediction: reconstructing burial history]]
* [[Analysis of mud weights]]
* [[Pressure prediction: analysis of mud weights]]
* [[Pressure prediction: analysis of cuttings]]
* [[Pressure prediction: analysis of cuttings]]
==References==
{{reflist}}
==External links==
==External links==
[[Category:Critical elements of the petroleum system]]
[[Category:Critical elements of the petroleum system]]
[[Category:Formation fluid pressure and its application]]
[[Category:Formation fluid pressure and its application]]
[[Category:Treatise Handbook 3]]