UNIVERSITY OF SOUTH ALABAMA
High Tech “Sonar” Techniques
MAS 603: Geological Oceanography
Lecture 23:
Geophysics 3: Sequence Stratigraphy
High Tech “Sonar” Techniques
•GLORIA: First deployed in
the 1980’s
High Tech “Sonar” Techniques
•GLORIA: First deployed in
the 1980’s
•Capable of surveying 18,000
km2 per day
•50 m resolution
High Tech “Sonar” Techniques
•GLORIA: First deployed in
the 1980’s
•Capable of surveying 18,000
km2 per day
High Tech “Sonar” Techniques
•TOBI: First deployed in the
late 1980’s
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High Tech “Sonar” Techniques
•TOBI: First deployed in the
late 1980’s
•Capable of 70 m penetration
High Tech “Sonar” Techniques
•TOBI: First deployed in the
late 1980’s
•Capable of 70 m penetration
•2 m resolution
Last Time
Geophysics
1) Introduction (various techniques)
2) Gravity
3) Side Scan Sonar Readings (Rikki)
4) Seismology Readings (Justin)
Geophysics
Two scales of geophysical analysis:
1) “small-scale” (shallow penetration seismic etc.)
2) “large-scale” (basin wide surveys)
Proposed well
http://www.spwla.org/library_info/glossary/reference/glossd/images/glsp32f1.gif
Gravity
http://www.ucmp.berkeley.edu/fosrec/images/ONeillFig8.jpg
Geophysical Techniques
Well logging uses multiple techniques to detect lithological changes
and oil/gas
FREEAIR
TOPOGRAPHY
By mixing which corrections you do, you
can produce different gravity maps of whole
countries…
BOUGUER
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Porosity Logs
Neutron Logs
Neutron Logs have a
radioactive source
(tritium?) that
generates neutrons.
As they pass into the
rock, they lose energy
(especially if they hit
similar atoms (e.g.,
hydrogen).
http://www.spwla.org/library_info/glossary/reference/glossd/images/glsp33f1.gif
Geophysical Techniques
Density Logs
Seismic Refraction - Measures travel times of seismic waves refracted
along a velocity contrast (propagation velocity and path controlled by
density and elastic moduli of the material through which waves pass)
The Density log is a measure of the
formation's bulk density and is
mostly used as a porosity measure.
Different lithologies can also be
determined using Density log based
on returned density value. For
example, pure quartz will have a
bulk density (g/cm-3) up to 2.65,
coal 1.2-1.8, halite 2.05, limestone
up to 2.75, dolomite up to 2.87,
anhydrite 2.98.
Geophone
http://www.resolve-geo.com/geophysical/index_clip_image004.jpg
Geophysical Techniques
Today’s Agenda
Seismic Stratigraphy uses wave reflections and refractions to resolve
surfaces between rock types (Acoustic Impedance)
Seismic Stratigraphy
•
•
•
Seismology (marine surveys)
Basic technique
Stratigraphy and quantifying sea level change
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Seismology
Seismology
Seismology (incl. seismic stratigraphy) is a means by which
to resolve the subsurface stratigraphy of the Earth
(sedimentary and igneous components).
It is favored by petroleum companies because of the speed of
analysis, extent of coverage and relative cheap cost.
15m
0.1 m
Penetration
(m)
Resolution
(m)
5m
1200m
0.01
0.1
1.0
10.0
100.0
Log Frequency (KHz)
Seismology
Seismology
15m
0.1 m
Penetration
(m)
Resolution
(m)
http://woodshole.er.usgs.gov/operations/sfmapping/images/seismic2.jpg
Typical acoustic techniques
http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236
5m
1200m
0.01
0.1
1.0
10.0
100.0
Log Frequency (KHz)
Seismology
Different devices are configured to resolve different features
(multibeam surveys)
Seismology (Marine Surveys)
Cost is also a factor
http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236
Marine seismic vessels are typically about 75 m [246 ft] long and travel about 5 knots [9.3 km/hr or
5.75 statute miles/hr] while towing arrays of air guns and streamers containing hydrophones a few
meters below the surface of the water. The tail buoy helps the crew locate the end of the streamers. The
air guns are activated periodically, such as every 25 m (about 10 seconds), and the resulting sound wave
travels into the Earth, is reflected back by the underlying rock layers to hydrophones on the streamer
and then relayed to the recording vessel.
http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236
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Seismology (Marine Surveys)
Seismology (Marine Surveys)
http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236
http://www.farallones.org/e_newsletter/2005-12/images/airguns05_000.jpg
Marine seismic vessels are typically about 75 m [246 ft] long and travel about 5 knots [9.3 km/hr or
5.75 statute miles/hr] while towing arrays of air guns and streamers containing hydrophones a few
meters below the surface of the water. The tail buoy helps the crew locate the end of the streamers. The
air guns are activated periodically, such as every 25 m (about 10 seconds), and the resulting sound wave
travels into the Earth, is reflected back by the underlying rock layers to hydrophones on the streamer
and then relayed to the recording vessel.
Seismology (Marine Surveys)
Seismology (Marine Surveys)
http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236
Marine seismic vessels are typically about 75 m [246 ft] long and travel about 5 knots [9.3 km/hr or
5.75 statute miles/hr] while towing arrays of air guns and streamers containing hydrophones a few
meters below the surface of the water. The tail buoy helps the crew locate the end of the streamers. The
air guns are activated periodically, such as every 25 m (about 10 seconds), and the resulting sound wave
travels into the Earth, is reflected back by the underlying rock layers to hydrophones on the streamer
and then relayed to the recording vessel.
http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236
Marine seismic data can be acquired using single streamers (second vessel) or multiple streamers (first
vessel) of various lengths or ocean bottom cable. 3D seismic data of various footprints, or areas covered
by an array of multiple towed streamers, are also routinely acquired (four vessels on the right).
Seismology (Marine Surveys)
Marine seismic acquisition can be performed by a source vessel and a recording vessel with
streamers or an ocean-bottom cable or, as shown here, seabed geophones. Energy from the
source vessel in the form of P-waves travels through the Earth and is reflected and
converted into P-waves and S-waves recorded by the receiver groups and relayed to the
recording vessel.
Seismology
The characteristic acoustic impedance of a geological medium is defined
as
Z0 = ρ x c
where
Z0 is the characteristic acoustic impedance ([M·L-2·T −1] or N·s/m3)
ρ is the density of the medium ([M·L−3]; kg/m³), and
c is the longitudinal wave speed or seismic velocity ([L·T −1]; m/s)
http://eied.deh.gov.au/coasts/mbp/south-east/maps/multiple/images/multi-ba.jpg
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Seismology
Seismology
Chalk Board
http://www.searchanddiscovery.net/documents/2004/brown05/images/01.htm
Synthetic seismic profiles are made from Sonic (Velocity) logs
Seismology
Well log data to synthetic seismic seismogram. A. Sonic log. B. Density log. C. Acoustic
impedance log. D. Log of seismic reflectivity. E. Broader shape of seismic energy pulse,
derived from reflectivity log. F. Synthetic seismogram.
Seismic Stratigraphy
http://www.seg.org/about/75/images/full/SEG75_64.jpg
Seismic Stratigraphy
Stratigraphic correlations
are made on the basis of
strong reflectors
Seismic section from the Upper Jurassic North Sea rift basin
indicating the development of a syncline in the hanging wall of
a large basin-bounding fault zone. This is related to the vertical
propagation of the fault.
http://www3.imperial.ac.uk/portal/pls/portallive/docs/1/3551902.JPG
Seismic Stratigraphy
Stratigraphic correlations
are made on the basis of
strong reflectors
Beware multiples!
http://utam.gg.utah.edu/stanford/img63.gif
http://utam.gg.utah.edu/stanford/img63.gif
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Seismic Stratigraphy
Seismic Stratigraphy
Planar features result in
disruptions to reflectors.
Planar features result in
disruptions to reflectors.
Spot the faults (2)
Spot the faults (2)
http://www.dmtcalaska.org/exploration/ISU/unit5/images/f25.jpg
Seismic Stratigraphy
http://openlearn.open.ac.uk/file.php/2292/S278_1_022i.jpg
http://www.dmtcalaska.org/exploration/ISU/unit5/images/f25.jpg
3D Seismic Modeling
3D visualisation in Landmark's GeoprobeTM software
illustrating the geometry of a growth fault array from the
Columbas Basin, offshore Trinidad. Data courtesy of BP
Trinidad.
http://www3.imperial.ac.uk/portal/pls/portallive/docs/1/4207902.JPG
Sequence Stratigraphy
Sequence Stratigraphy
A Short History
A Short History
Meet Peter Vail. A man who was on a quest and in so doing,
changed the way geophysists and sedimentologists think
(literally).
Vail was a geophysist at EXXON in Houston and in the 1960’s
began to consider what those surfaces on seismic traces really
were.
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Sequence Stratigraphy
Sequence Stratigraphy
A Short History
A Short History
"Pete's ideas evolved naturally from his first
pioneering work on the importance of stratal
surfaces in rocks as geologic time lines," wrote
Robert Mitchum, a longtime friend and former
Exxon colleague.
"He soon recognized the cyclic occurrence of
bundles of strata he called sequences in well logs,
seismic reflections and outcrops.
Lateral and vertical
changes in sedimentary
deposits give rise to
distinct stacking
patterns…
"Observing that sequence boundaries appear
synchronous globally, he postulated that cyclic
eustatic sea level changes are major controls on
stratigraphy, along with basin tectonics and
sediment supply," Mitchum said.
"This realization led to the development of
eustatic cycle charts”. (2003 AAPG Address)
Sequence Stratigraphy
Sequence Stratigraphy
A Short History
A Short History
… which can be used to resolve
how sea level has changes over
time. The “Vail Curve” is
synonymous with eustasy
And is used by
everyone in soft
rock geology.
•stratigraphers
•sedimentologists
•paleontologists
•petroleum geol.
Sequence Stratigraphy
Sequence Stratigraphy
A Short History
A Short History
Ultimately it works because sea level controls what sediment
is produced and where it is deposited.
http://strata.geol.sc.edu/terminology/system-tract.html
Accommodation Space: The thickness of sediment that can be
deposited (it’s sea level-controlled)
http://strata.geol.sc.edu/terminology/system-tract.html
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Sequence Stratigraphy
Sequence Stratigraphy
A Short History
A Short History
Note: Vail’s surfaces
actually define
packages of
sedimentary rock.
Accommodation
Space:
(+) with sea level
highstands;
highstands
Those associated
with specific states
of sea level are
called systems tracts.
tracts
(-) with sea level
lowstands
http://strata.geol.sc.edu/terminology/system-tract.html
Sequence Stratigraphy (System Tracts)
System Tracts come in numerous styles and are named
according to sea level position/state during deposition.
The 5 most important are
1) LST:
LST Low stand systems tract
2) HST:
HST High stand systems tract
3) TST:
TST Transgressive systems tract
4) FSST:
FSST Falling stage systems tract
5) RST:
FRST)
RST Regressive systems tract (FRST
Sequence Stratigraphy (Surfaces)
http://strata.geol.sc.edu/terminology/system-tract.html
Sequence Stratigraphy (Surfaces)
System Tracts are
bounded by several
important surfaces
1) Sequence Boundaries
2) MFS
3) Transgressive Surface
4) Correlative conformity
Sequence Stratigraphy (System Tracts)
LST: Low stand systems tract: includes deposits that
accumulate after the onset of relative a sea-level rise.
http://strata.geol.sc.edu/terminology/system-tract.html
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Sequence Stratigraphy (System Tracts)
Sequence Stratigraphy (System Tracts)
LST: Low stand systems tract: includes deposits that
accumulate after the onset of relative a sea-level rise.
LST: Low stand systems tract: includes deposits that
accumulate after the onset of relative a sea-level rise.
Lowstand Systems Tract sediments often fill or partially infill
incised valleys that were cut into the Highstand Systems Tract,
and other earlier deposits, during the FSST.
Lowstand Systems Tract sediments often fill or partially infill
incised valleys that were cut into the Highstand Systems Tract,
and other earlier deposits, during the FSST.
Stacking patterns exhibit [backstepping, onlapping,
retrogradational, aggrading clinoforms that thicken up-dip].
http://strata.geol.sc.edu/terminology/system-tract.html
Sequence Stratigraphy (System Tracts)
Sequence Stratigraphy (System Tracts)
…and that the nature of the surfaces can tell you the stage(s)
of sea level during deposition.
Clinoforms are parallel but inclined surfaces
http://strata.geol.sc.edu/terminology/system-tract.html
Sequence Stratigraphy (System Tracts)
http://strata.geol.sc.edu/terminology/system-tract.html
http://strata.geol.sc.edu/terminology/system-tract.html
Sequence Stratigraphy (System Tracts)
http://strata.geol.sc.edu/terminology/system-tract.html
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Sequence Stratigraphy (System Tracts)
LST: Low stand systems tract: includes deposits that accumulate
after the onset of relative a sea-level rise.
http://strata.geol.sc.edu/terminology/system-tract.html
Sequence Stratigraphy (System Tracts)
HST: High stand systems tract: the progradational deposits that
form when sediment accumulation rates exceed the rate of
increase in accommodation space. Stacking patterns exhibit
prograding aggrading clinoforms that thin upward.
Sequence Stratigraphy (System Tracts)
HST: High stand systems tract: the progradational deposits that
form when sediment accumulation rates exceed the rate of
increase in accommodation space. Stacking patterns exhibit
prograding aggrading clinoforms that thin upward.
http://strata.geol.sc.edu/terminology/system-tract.html
Upcoming Stuff
Wednesday: Isotope Stratigraphy Readings (Heather)
Next Monday : Seismology and BIFs (Kate)
Earth history papers are due now
http://strata.geol.sc.edu/terminology/system-tract.html
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