Changes

  | part    = Critical elements of the petroleum system

  | part    = Critical elements of the petroleum system

  | chapter = Sedimentary basin analysis

  | chapter = Sedimentary basin analysis

  | frompg  = 4-1

  | frompg  = 4-40

  | topg    = 4-123

  | topg    = 4-44

  | author  = John M. Armentrout

  | author  = John M. Armentrout

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm

==Building regional log cross sections==

==Building regional log cross sections==

Regional stratigraphic well-log [[cross section]]s form the foundation for many basin studies. They give a regional view of basin stratigraphy and can be integrated with seismic and biostratigraphic data. The table below outlines the steps for building regional well-log cross sections.

Regional stratigraphic well-log [[cross section]]s form the foundation for many basin studies. They give a regional view of basin stratigraphy and can be integrated with seismic and biostratigraphic data. The list below outlines the steps for building regional well-log cross sections.

# Build a grid of well-log sections that crosses the entire basin, either along depositional [[dip]] or depositional strike. Use as many wells as practical. Where available, add measured sections and [[core description]]s to the grid.

# Correlate cross sections. Look for [[Unconformity|unconformities]] and flooding surfaces.

# Tie the correlations from depositional-dip sections to depositional-strike sections.

# Confirm correlations on seismic reflection profiles.

| Build a grid of well-log sections that crosses the entire basin, either along depositional dip or depositional strike. Use as many wells as practical. Where available, add measured sections and [[core description]]s to the grid.

| Correlate cross sections. Look for [[Unconformity|unconformities]] and flooding surfaces.

| Tie the correlations from depositional-dip sections to depositional-strike sections.

| Confirm correlations on seismic reflection profiles.

==Biostratigraphic patterns==

==Biostratigraphic patterns==

Using chronostratigraphically significant bioevents as defined by microfossil extinction events and abundance patterns, local cycles of transgression and [[Wikipedia:Marine_regression|regression]] can be correlated from well to well, providing a high-resolution calibration of depositional cyclicity. Patterns of relative dilution vs. concentration of fossils that correlate over a significant geographic area, such as a large portion of a basin margin, can be interpreted as reflecting cycles of regional transgression and regression rather than local lateral shifting of sediment input points.

Using chronostratigraphically significant bioevents as defined by microfossil extinction events and abundance patterns, local cycles of transgression and [[regression]] can be correlated from well to well, providing a high-resolution calibration of depositional cyclicity. Patterns of relative dilution vs. concentration of fossils that correlate over a significant geographic area, such as a large portion of a basin margin, can be interpreted as reflecting cycles of regional transgression and regression rather than local [[lateral]] shifting of sediment input points.

Stratigraphic intervals rich in calcareous nannoplankton and foraminiferal fossils and having maximum gamma-ray values are interpreted to correlate with condensed depositional intervals deposited during relative sediment starvation related to transgression.<ref name=ch04r59>Loutit, T., S., Hardenbol, J., Vail, P., R., Baum, G., R., 1988, Condensed sections: the key to age determination and correlation of continental margin sequences: SEPM Special Publication 42, p. 183–213.</ref> Intervals devoid of fossils or having low abundance values, often associated with sandy lithofacies, can be interpreted as deposited during relative high rates of accumulation related to [[Depocenter#Sediment_supply_rate_and_facies_patterns|progradation]] of the sediment supply into the area of the well, marking a phase of regression. Biofacies are interpreted using benthic foraminiferal assemblages indicative of water mass conditions.<ref name=ch04r97>Tipsword, H., L., J., Setzer, F., M., Smith, F., L. Jr., 1966, Interpretation of depositional environment in Gulf Coast exploration from paleoecology and related stratigraphy: Gulf Coast Assoc. of Geological Societies Transactions, vol. 16, p. 119–130.</ref><ref name=ch04r28>Culver, S., J., 1988, New foraminiferal depth zonation of the northwestern Gulf of Mexico: Palaios, vol. 3, p. 69–85., 10., 2307/3514545</ref><ref name=ch04r7>Armentrout, J., M., 1991, Paleontological constraints on depositional [[modeling]]: examples of integration of biostratigraphy and seismic stratigraphy, Pliocene–Pleistocene, Gulf of Mexico, in Weimer, P., Link, M., H., eds., Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems: New York, Springer-Verlag, p. 137–170.</ref>

Stratigraphic intervals rich in calcareous nannoplankton and foraminiferal fossils and having maximum gamma-ray values are interpreted to correlate with condensed depositional intervals deposited during relative sediment starvation related to transgression.<ref name=ch04r59>Loutit, T., S., Hardenbol, J., Vail, P., R., Baum, G., R., 1988, Condensed sections: the key to age determination and correlation of continental margin sequences: SEPM Special Publication 42, p. 183–213.</ref> Intervals devoid of fossils or having low abundance values, often associated with sandy [[lithofacies]], can be interpreted as deposited during relative high rates of accumulation related to [[Depocenter#Sediment_supply_rate_and_facies_patterns|progradation]] of the sediment supply into the area of the well, marking a phase of regression. Biofacies are interpreted using benthic foraminiferal assemblages indicative of water mass conditions.<ref name=ch04r97>Tipsword, H., L., J., Setzer, F., M., Smith, F., L. Jr., 1966, Interpretation of depositional environment in Gulf Coast exploration from paleoecology and related stratigraphy: Gulf Coast Assoc. of Geological Societies Transactions, vol. 16, p. 119–130.</ref><ref name=ch04r28>Culver, S., J., 1988, New foraminiferal depth zonation of the northwestern Gulf of Mexico: Palaios, vol. 3, p. 69–85., 10., 2307/3514545</ref><ref name=ch04r7>Armentrout, J., M., 1991, Paleontological constraints on depositional [[modeling]]: examples of integration of biostratigraphy and seismic stratigraphy, Pliocene–Pleistocene, Gulf of Mexico, in Weimer, P., Link, M., H., eds., Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems: New York, Springer-Verlag, p. 137–170.</ref>

==GOM basin example==

==GOM basin example==

In the GOM basin, variations in well-log response and [[Fossil assemblage|biofacies]] distribution are analyzed for recognition of stacked depositional sequences. The [[Basic open hole tools#Gamma ray|gamma-ray]] log display provides a measure of sediment type, with curve deflections to the left suggesting increased sand content while high values to the right indicate increases in clay content. Use of multiple logs, especially [[Basic open hole tools#Spontaneous potential|spontaneous potential]], [[Basic open hole tools#Resistivity|resistivity]], density, and velocity logs calibrated by well-cutting descriptions and formation microscanner displays, provides a data set for reliable rock type identification. The figure below illustrates an interpretation template for log motif analysis.

In the GOM basin, variations in well-log response and [[Fossil assemblage|biofacies]] distribution are analyzed for recognition of stacked depositional sequences. The [[Basic open hole tools#Gamma ray|gamma-ray]] log display provides a measure of sediment type, with curve deflections to the left suggesting increased sand content while high values to the right indicate increases in clay content. Use of multiple logs, especially [[Basic open hole tools#Spontaneous potential|spontaneous potential]], [[Basic open hole tools#Resistivity|resistivity]], density, and velocity logs calibrated by well-cutting descriptions and formation microscanner displays, provides a data set for reliable rock type identification. The figure below illustrates an interpretation template for log motif analysis.

Patterns of forestepping vs. backstepping log-motif funnels can define transgressive vs. regressive depositional trends and candidate systems tracts and sequences. Vail and Wornardt<ref name=ch04r101>Vail, P., R., Wornardt, W., W., 1990, Well log seismic stratigraphy: a new tool for exploration in the '90s: Proceedings, Gulf Coast Section SEPM 11th Annual Research conference, p. 379–388.</ref> and Armentrout et al.<ref name=ch04r8>Armentrout, J. M., S. J. Malacek, L. B. Fearn, C. E. Sheppard, P. H. Naylor, A. W. Miles, R. J. Desmarais, and R. E. Dunay, 1993, Log-motive analysis of Paleogene depositional systems tracts, central and northern North Sea: Defined by sequence stratigraphic analysis ''in'' J. R. Parker, ed., Petroleum Geology of Northwest Europe: Proceedings of the 4th Conference, The Geological Society of London, p. 45-57.</ref> detail the process.

Patterns of forestepping vs. backstepping log-motif funnels can define transgressive vs. [[Regression|regressive]] depositional trends and candidate systems tracts and sequences. Vail and Wornardt<ref name=ch04r101>Vail, P., R., Wornardt, W., W., 1990, Well log seismic stratigraphy: a new tool for exploration in the '90s: Proceedings, Gulf Coast Section SEPM 11th Annual Research conference, p. 379–388.</ref> and Armentrout et al.<ref name=ch04r8>Armentrout, J. M., S. J. Malacek, L. B. Fearn, C. E. Sheppard, P. H. Naylor, A. W. Miles, R. J. Desmarais, and R. E. Dunay, 1993, Log-motive analysis of Paleogene depositional systems tracts, central and northern North Sea: Defined by sequence stratigraphic analysis ''in'' J. R. Parker, ed., Petroleum Geology of Northwest Europe: Proceedings of the 4th Conference, The Geological Society of London, p. 45-57.</ref> detail the process.

==GOM basin example chart==

==GOM basin example chart==

</gallery>

</gallery>

The histogram patterns of foraminiferal and calcareous nannoplankton abundance for the South Galveston Mobil A-158 #3 well are shown in [[:file:sedimentary-basin-analysis_fig4-23.png|Figure 3]]. The histogram is based on a detailed checklist of the relative abundance of each species of fossil in each well-cutting sample.<ref name=ch04r10>Armentrout, J., M., Clement, J., F., 1990, Biostratigraphic calibration of depositional cycles: a case study in High Island–Galveston–East Breaks areas, offshore Texas: Proceedings, Gulf Coast Section SEPM 11th Annual Research Conference, p. 21–51.</ref> Display of this data in two-way time facilitates integration with seismic reflection profiles using the [[synthetic seismogram]] to match the well data with the seismic reflection profile at the well site. Patterns of shallow vs. deep [[Fossil assemblage|biofacies]] and fossil abundance (i.e., concentration vs. dilution) can be correlated with [[Depocenter#Sediment_supply_rate_and_facies_patterns|progradation]] of sandstone vs. mudstone interpreted from wireline log patterns. Bioevents (abbreviated acronyms such as 2B and SG) and faunal discontinuity events (abbreviated FDA-3 and FDA-4) provide correlation horizons between which the abundance patterns provide additional events for correlation.<ref name=ch04r7 />

The histogram patterns of foraminiferal and calcareous nannoplankton abundance for the South Galveston Mobil A-158 #3 well are shown in [[:file:sedimentary-basin-analysis_fig4-23.png|Figure 3]]. The histogram is based on a detailed checklist of the relative abundance of each species of fossil in each well-cutting sample.<ref name=ch04r10>Armentrout, J., M., Clement, J., F., 1990, Biostratigraphic calibration of depositional cycles: a case study in High Island–Galveston–East Breaks areas, offshore Texas: Proceedings, Gulf Coast Section SEPM 11th Annual Research Conference, p. 21–51.</ref> Display of this data in two-way time facilitates integration with seismic reflection profiles using the [[synthetic seismogram]] to match the well data with the seismic reflection profile at the well site. Patterns of shallow vs. deep [[Fossil assemblage|biofacies]] and fossil abundance (i.e., concentration vs. dilution) can be correlated with [[Depocenter#Sediment_supply_rate_and_facies_patterns|progradation]] of sandstone vs. [[mudstone]] interpreted from wireline log patterns. Bioevents (abbreviated acronyms such as 2B and SG) and faunal discontinuity events (abbreviated FDA-3 and FDA-4) provide correlation horizons between which the abundance patterns provide additional events for correlation.<ref name=ch04r7 />

In the histogram in [[:file:sedimentary-basin-analysis_fig4-23.png|Figure 3]] (see [[:file:sedimentary-basin-analysis_fig4-17.png|Figure 1]] for well location), the foraminiferal abundance scale is 0-1000 specimens and the nannoplankton abundance scale is 0-800 specimens. Biofacies include inner neritic (IN, 0-50 m), middle neritic (MN, 50-100 m), outer neritic (ON, 100-200 m), upper bathyal (UPPB, 200-500 m), middle bathyal (MDLB, 500-1000 m), and lower bathyal (LOWB, 1000–2000 m). This figure is the leftmost (southern) well panel in [[:file:sedimentary-basin-analysis_fig4-24.png|Figure 4]]. The wireline log (gamma ray) motif patterns ([[:file:sedimentary-basin-analysis_fig4-22.png|Figure 2]]), biostratigraphic abundance events, and extinction datums provide correlation events.

In the histogram in [[:file:sedimentary-basin-analysis_fig4-23.png|Figure 3]] (see [[:file:sedimentary-basin-analysis_fig4-17.png|Figure 1]] for well location), the foraminiferal abundance scale is 0-1000 specimens and the nannoplankton abundance scale is 0-800 specimens. Biofacies include inner neritic (IN, 0-50 m), middle neritic (MN, 50-100 m), outer neritic (ON, 100-200 m), upper bathyal (UPPB, 200-500 m), middle bathyal (MDLB, 500-1000 m), and lower bathyal (LOWB, 1000–2000 m). This figure is the leftmost (southern) well panel in [[:file:sedimentary-basin-analysis_fig4-24.png|Figure 4]]. The wireline log (gamma ray) motif patterns ([[:file:sedimentary-basin-analysis_fig4-22.png|Figure 2]]), biostratigraphic abundance events, and extinction datums provide correlation events.

==See also==

==See also==

* [[Depositional sequence]]

* [[East Breaks depositional sequence]]

* [[Definitions of depositional system elements]]

* [[Definitions of depositional system elements]]

* [[Identifying depositional sequences]]

* [[Identifying depositional sequences]]

[[Category:Critical elements of the petroleum system]]  

[[Category:Critical elements of the petroleum system]]  

[[Category:Sedimentary basin analysis]]

[[Category:Sedimentary basin analysis]]