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  = 21-27

  | topg    = 21-68

  | topg    = 21-28

  | 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

==Objective==

==Objective==

The objective of seismic sequence analysis is to identify [[depositional sequence]]s and [[Systems tracts identification|systems tracts]] on [[Seismic data|seismic sections]] by interpreting the location of their boundaries. Boundaries are manifested as discontinuities in seismic sections and are located mainly by finding [http://wiki.seg.org/wiki/Dictionary:Reflection reflection] terminations.<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>

The objective of seismic sequence analysis is to identify [[Depositional sequence identification|depositional sequence]]s and [[Systems tracts identification|systems tracts]] on [[Seismic data|seismic sections]] by interpreting the location of their boundaries. Boundaries are manifested as discontinuities in seismic sections and are located mainly by finding [http://wiki.seg.org/wiki/Dictionary:Reflection reflection] terminations.<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 A. W. Bally, ed., Atlas of seismic stratigraphy: [http://store.aapg.org/detail.aspx?id=478 AAPG Studies in Geology 27], p. 1-10.</ref>

==Procedure==

==Procedure==

Follow the steps listed in the table below to perform a sequence analysis of a seismic section (adapted from Vail<ref name=ch21r44 />).

Follow the steps listed below to perform a sequence analysis of a seismic section (adapted from Vail<ref name=ch21r44 />).

# Look for places where two [http://wiki.seg.org/wiki/Dictionary:Reflector reflectors] converge. Where reflectors converge, there will be terminations.

# Mark the [http://wiki.seg.org/wiki/Dictionary:Reflection reflection] terminations with arrows.

# Draw in the discontinuity surface between the [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=onlap onlapping] and [http://www.glossary.oilfield.slb.com/en/Terms/d/downlap.aspx downlapping] reflections above, and the truncating and [http://homepage.ufp.pt/biblioteca/Seismic/Pages/Page22.htm toplapping] reflectors above. If the discontinuity surface becomes conformable, trace its position across the section by reflection correlation.

# Continue the process described in steps 1, 2, and 3 for all the seismic lines in the grid.

# Close all seismic grid loops by checking the loop ties for each discontinuity or its correlative equivalent.

# Categorize each discontinuity.

| Look for places where two [http://wiki.seg.org/wiki/Dictionary:Reflector reflectors] converge. Where reflectors converge, there will be terminations.

#* '''If''' it is characterized by regional onlap above and truncation below '''then''' it is probably a [[Definitions_of_depositional_system_elements#Sequence_boundaries|sequence boundary]]

#* '''If''' it is characterized by regional downlap '''then''' it is most likely a downlap surface

| Mark the [http://wiki.seg.org/wiki/Dictionary:Reflection reflection] terminations with arrows.

| Draw in the discontinuity surface between the [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=onlap onlapping] and [http://www.glossary.oilfield.slb.com/en/Terms/d/downlap.aspx downlapping] reflections above, and the truncating and [http://homepage.ufp.pt/biblioteca/Seismic/Pages/Page22.htm toplapping] reflectors above. If the discontinuity surface becomes conformable, trace its position across the section by reflection correlation.

| Continue the process described in steps 1, 2, and 3 for all the seismic lines in the grid.

| Close all seismic grid loops by checking the loop ties for each discontinuity or its correlative equivalent.

| Categorize each discontinuity.

* '''If''' it is characterized by regional onlap above and truncation below '''then''' it is probably a [[Definitions_of_depositional_system_elements#Sequence_boundaries|sequence boundary]]

* '''If''' it is characterized by regional downlap '''then''' it is most likely a downlap surface

==Marking a seismic section, marking==

==Marking a seismic section, marking==

{| class = "wikitable"

{| class = "wikitable"

|-

|-

! Feature

! Feature || Color

! Color

|-

|-

| Reflection terminations and reflection patterns

| Reflection terminations and reflection patterns || Red

| Red

|-

|-

| Downlap surfaces

| Downlap surfaces || Green

| Green

|-

|-

| Transgressive surfaces

| Transgressive surfaces || Blue

| Blue

|-

|-

| Sequence boundaries

| Sequence boundaries || Miscellaneous

| Miscellaneous

|}

|}

{| class = "wikitable"

{| class = "wikitable"

|-

|-

! Reflection termination point

! Reflection termination point || Pattern || Associated discontinuity

! Pattern

! Associated discontinuity

|-

|-

| rowspan=2 | Above a discontinuity

| rowspan=2 | Above a discontinuity || [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=onlap Onlap] || [[Definitions_of_depositional_system_elements#Sequence_boundaries|Sequence boundary]] ([[unconformity]])

| Onlap

| Sequence boundary ([[unconformity]])

|-

|-

| Downlap

| [http://www.glossary.oilfield.slb.com/en/Terms/d/downlap.aspx Downlap] || Downlap surface (condensed section)

| Downlap surface (condensed section)

|-

|-

| rowspan=3 | Below a discontinuity

| rowspan=3 | Below a discontinuity || Truncation || Sequence boundary

| Truncation

| Sequence boundary

|-

|-

| Toplap

| [http://homepage.ufp.pt/biblioteca/Seismic/Pages/Page22.htm Toplap] || Sequence boundary

| Sequence boundary

|-

|-

| Apparent truncation

| Apparent truncation || Downlap surface

| Downlap surface

|}

|}

==Locating reflection terminations==

==Locating reflection terminations==

Locating reflection termination is a matter of finding the patterns described in the table above. [[:file:exploring-for-stratigraphic-traps_fig21-18.png|Figure 1]] shows these patterns and the associated discontinuity surfaces.

Locating reflection termination is a matter of finding the patterns described in the table above. [[:file:exploring-for-stratigraphic-traps_fig21-18.png|Figure 1]] shows these patterns and the associated discontinuity surfaces.

==See also==

==See also==

[[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]]