Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Exploring for stratigraphic traps

  | chapter = Exploring for stratigraphic traps

  | frompg  = 21-1

  | frompg  = 21-29

  | topg    = 21-68

  | topg    = 21-31

  | author  = John C. Dolson, Mike S. Bahorich, Rick C. Tobin, Edward A. Beaumont, Louis J. Terlikoski, Michael L. Hendricks

  | author  = John C. Dolson, Mike S. Bahorich, Rick C. Tobin, Edward A. Beaumont, Louis J. Terlikoski, Michael L. Hendricks

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch21/ch21.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch21/ch21.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

After seismic sections have been analyzed for sequences, well logs are analyzed for sequences and systems tracts. This involves interpreting depositional lithofacies on logs using cuttings and cores and then identifying sequences and systems tracts from the interpreted logs. Stacking patterns displayed in cross sections and individual logs show accommodation space changes which help us identify sequence and systems tracts.

After seismic sections have been analyzed for sequences, well logs are analyzed for sequences and systems tracts. This involves interpreting depositional [[lithofacies]] on logs using cuttings and cores and then identifying sequences and systems tracts from the interpreted logs. Stacking patterns displayed in [[cross section]]s and individual logs show accommodation space changes which help us identify sequence and systems tracts.

==Procedure==

==Procedure==

The table below, modified from Vail<ref name=ch21r44>Vail, P., R., 1987, Seismic stratigraphy interpretation procedure, in Bally, A., W., ed., Atlas of Seismic Stratigraphy: AAPG Studies in Geology No. 27, p. 2.</ref> outlines a suggested procedure for well log sequence analysis.

The list below, modified from Vail<ref name=ch21r44>Vail, P., R., 1987, [http://archives.datapages.com/data/specpubs/oversiz2/data/a188/a188/0001/0000/0001.htm Seismic stratigraphy interpretation procedure], in Bally, A., W., ed., Atlas of Seismic Stratigraphy: [http://store.aapg.org/detail.aspx?id=478 AAPG Studies in Geology No. 27], p. 2.</ref> outlines a suggested procedure for well log sequence analysis.

# Interpret depositional lithofacies on logs using cores and cuttings to calibrate the log.

# Estimate sequences and systems tracts from the interpreted lithofacies using regional [[cross section]]s with well and [http://www.merriam-webster.com/dictionary/outcrop outcrop] data.

# Determine accommodation space changes from parasequence stacking patterns seen in well log cross sections (see below).

# Check estimates of sequences and systems tracts:

#*  Correlate between wells that have biostratigraphic-time correlations, well log marker-bed correlations, and the global sea cycle chart.

#*  Correlate with seismic profiles.

| Interpret depositional lithofacies on logs using cores and cuttings to calibrate the log.

| Estimate sequences and systems tracts from the interpreted lithofacies using regional cross sections with well and outcrop data.

| Determine accommodation space changes from parasequence stacking patterns seen in well log cross sections (see below).

| Check estimates of sequences and systems tracts:

*  Correlate between wells that have biostratigraphic-time correlations, well log marker-bed correlations, and the global sea cycle chart.

*  Correlate with seismic profiles.

==Parasequence stacking patterns==

==Parasequence stacking patterns==

Parasequences stack into three basic patterns as a result of the interaction of accommodation and rate of sediment supply:

 

 

Parasequences stack into [[Depocenter#Sediment_supply_rate_and_facies_patterns|three basic patterns]] as a result of the interaction of accommodation and rate of sediment supply:

* Progradational

* Progradational

* Retrogradational

* Retrogradational

* Aggradational

* Aggradational

[[:file:exploring-for-stratigraphic-traps_fig21-19.png|Figure 1]] shows these three stacking patterns.

 

[[file:exploring-for-stratigraphic-traps_fig21-19.png|thumb|{{figure number|21-19}}.]]

==Stacking patterns for systems tracts==

==Stacking patterns for systems tracts==

Systems tracts often have characteristic parasequence stacking patterns. Stacking patterns of the basin-floor fan and slope fan, contained within the lowstand systems tract, are difficult to identify. The table below summarizes typical stacking patterns for the three systems tracts.

Systems tracts often have characteristic parasequence stacking patterns. Stacking patterns of the [http://www.sepmstrata.org/TerminologyList.aspx basin-floor fan] and slope fan, contained within the lowstand systems tract, are difficult to identify. The table below summarizes typical stacking patterns for the three systems tracts.

{| class = "wikitable"

{| class = "wikitable"

==Log patterns for systems tracts==

==Log patterns for systems tracts==

[[file:exploring-for-stratigraphic-traps_fig21-20.png|thumb|{{figure number|21-20}}Modified. Copyright: Hyne, 1995; courtesy Tulsa Geological Society.]]

[[file:exploring-for-stratigraphic-traps_fig21-20.png|300px|thumb|{{figure number|2}}Characteristic parasequence stacking patterns for the high-stand (HST), transgressive (TST), and lowstand (LST) systems tracts of a passive margin basin third-order depositional sequence. Modified. Copyright: Hyne;<ref name=Hyne /> courtesy Tulsa Geological Society.]]

 

==LST example==

==LST example==

[[file:exploring-for-stratigraphic-traps_fig21-21.png|thumb|{{figure number|21-21}}.]]

[[file:exploring-for-stratigraphic-traps_fig21-21.png|300px|thumb|{{figure number|3}}Cross section from the Late Cenozoic of the Gulf of Mexico. From Mitchum et al.;<ref>Mitchum, R. M., P. R. Vail, and J. B. Sangree, 1977, [http://archives.datapages.com/data/specpubs/seismic1/data/a165/a165/0001/0100/0117.htm Seismic stratigraphy and global changes in sea level, part 6: stratigraphic interpretations of seismic reflection patterns in depositional sequences], in C. E. Payton, ed., Seismic Stratigraphy and Applications to Hydrocarbon Exploration: [http://store.aapg.org/detail.aspx?id=1157 AAPG Memoir 26], p. 117–133.</ref> courtesy AAPG.]]

 

The cross section in [[:file:exploring-for-stratigraphic-traps_fig21-21.png|Figure 3]] is from the Late [[Cenozoic]] of the [[Gulf of Mexico]]. It shows the well log responses of a lowstand systems tract (labeled as PGC, or prograding complex, on the cross section). Log A is completely basinal with a slope fan overlain by shingled [[turbidite]]s. Logs B and C have deltaic and delta front sands, and midslope turbidite sands. Log D has a “classic” coarsening-upward pattern. Log E has incised valley sands.

==See also==

==See also==

* [[Seismic sequence analysis]]

* [[Seismic sequence analysis]]

* [[Combining well log with seismic sequence analysis]]

* [[Combining well log with seismic sequence analysis]]

==References==

==References==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Exploring for stratigraphic traps]]

[[Category:Exploring for stratigraphic traps]]