The Tools of Subsurface Analysis

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The Tools of Subsurface Analysis
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Well Logs
Delimit of surfaces identify sediments
penetrated

• Resistivity Logs
• Spontaneous Potential (SP) Logs
• Gamma Ray Logs
• Neutron Logs
• Density Logs
• Sonic (acoustic) Logs

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Well Logs
Delimit of surfaces identify sediments
penetrated

• Resistivity Logs
• Spontaneous Potential (SP) Logs
• Gamma Ray Logs
• Neutron Logs
• Density Logs
• Sonic (acoustic) Logs

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Well Logs
Delimit of surfaces identify sediments
penetrated

• Resistivity Logs
• Spontaneous Potential (SP) Logs
• Gamma Ray Logs
• Neutron Logs
• Density Logs
• Sonic (acoustic) Logs

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Well Logs
Delimit of surfaces identify sediments
penetrated

• Resistivity Logs
• Spontaneous Potential (SP) Logs
• Gamma Ray Logs
• Neutron Logs
• Density Logs
• Sonic (acoustic) Logs

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Well Logs
Delimit of surfaces identify sediments
penetrated

• Resistivity Logs
• Spontaneous Potential (SP) Logs
• Gamma Ray Logs
• Neutron Logs
• Density Logs
• Sonic (acoustic) Logs

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The Tools of Subsurface Analysis
Facies analysis of subsurface data depends on
tools which delimit of surfaces and provide clues
as to the sediments they contain

• Well logs
• Cores
• Seismic
• Gravity magnetics

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Well Logs Versus Seismic

• Well logs
• Great vertical resolution
• Delimit bounding surfaces
• Establish lithology of sediments penetrated
• Seismic
• Great lateral continuity and resolution
• Define gross sediment geometry

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Tools are Keys to Allostratigraphy Sequence
Stratigraphy

• Allostratigraphy
• bounding discontinuities including erosion
  surfaces, marine flooding surfaces, tuffs,
  tempestite, and/or turbidite boundaries etc. as
  time markers
• Sequence Stratigraphy higher level
  allostratigraphic model which interprets
  depositional origin of sedimentary strata as
  products of "relative sea level change"

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The Tools of Subsurface Analysis
Facies analysis of subsurface data depends on
tools which delimit of surfaces and provide clues
as to the sediments they contain

• Well logs
• Seismic

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Well Logs
Delimit of surfaces identify sediments
penetrated

• Resistivity Logs
• Spontaneous Potential (SP) Logs
• Gamma Ray Logs
• Neutron Logs
• Density Logs
• Sonic (acoustic) Logs

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Resistivity Logs
The most commonly used logs

• Measures resistance of flow of electric current
• Is function of porosity pore fluid in rock
• Frequently used to identify lithology

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Spontaneous Potential (SP) Logs
Next most common log

• Measures electrical current in well
• Result of salinity differences between formation
  water and the borehole mud
• Separates bed boundaries of permeable sands
  impermeable shales.

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Gamma Ray Logs
Another common log

• Records radioactivity of a formation
• Shales have high gamma radioactive response
• Gamma ray logs infer grain size (and so
  subsequently inferred depositional energy)
• Gamma ray logs are most commonly used logs for
  sequence stratigraphic analysis

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After Harris Saller 1999
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Neutron Logs
Another common log

• Measures porosity of formation
• Uses quantity of hydrogen present
• Measures lithology when used with Density Log

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Density Logs
A common log

• Measures formations bulk density
• Used as a porosity measure
• Differentiates lithologies with Neutron Log
• Used with Sonic Logs to generate synthetic
  seismic traces to match to seismic lines

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Sonic (Acoustic) Logs
Another common log

• Measures of speed of sound in formation
• Tied to porosity and lithology
• Used with Density Logs to generate Synthetic
  Seismic traces to match to Seismic lines

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The Tools of Subsurface Analysis
Facies analysis of subsurface data depends on
tools which delimit of surfaces and provide clues
as to the sediments they contain

• Well logs
• Seismic

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Seismic
Seismic stratigraphic interpretation used to

• Define geometries of genetic reflection packages
  that envelope seismic sequences and systems
  tracts
• Identify bounding discontinuities on basis of
  reflection termination patterns and continuity

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Seismic Boundaries
Termination below discontinuity, or upper
sequence boundary

• Toplap termination
• Truncation of sediment surface
• Often channel bottom

Above a discontinuity defining lower sequence
boundary

• Onlap over surface
• Downlap surface

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Seismic Boundaries
Below Boundary - Toplap termination
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Seismic Boundaries
Below Boundary - Truncation of surface
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Seismic Boundaries
Channeled Surface Below Boundary
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Seismic Boundaries
Over Boundary - Onlap onto surface
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Seismic Boundaries
Over Boundary- Downlap onto surface
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Sequence Stratigraphy
Subdivision interpretation of sedimentary
record using a framework surfaces seen in
outcrops, well logs, 2-D and 3-D seismic.
Include

• Surfaces of erosion non-deposition (sequence
  boundaries)
• Flooding (trangressive surfaces TS /or maximum
  flooding surfaces mfs) high stand condensed
  surfaces

This framework used to predict the extent of
sedimentary facies geometry, lithologic
character, grain size, sorting reservoir quality
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Tools Define Bounding Surfaces
These surfaces subdivide sedimentary rock
provide-

• Relative time framework for sedimentary
  succession
• Better understanding of inter-relationship of
  depositional settings their lateral correlation

Conceptual models follow that link the processes
that formed the sediments and enable the
prediction of their gross geometries
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Hierarchy of Geometries

• Sequence geometries are subdivided and defined by
• Maximum Flooding Surfaces (mfs)
• Transgressive Surfaces (TS)
• Sequence Boundaries (SB)
• Define how vertical succession or stacking
  patterns of unconfined sheets are arranged
• Prograde (step seaward)
• Retrograde (step landward)
• Aggrade (build vertically)
• Sheets and unconfined lobes may contain
• Non-amalgamated bodies
• Amalgamated, multi-storied bodies
• Incised topographic fill of valleys
• Unconfined but localized lobes from point
  multiple up dip sources
• Unconfined but localized build ups (carbonates)

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Delta Mouth Bar - Kentucky
Note Incised Surface
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Channel Gulf Coast
Note Incised Surface
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Flood Deltas Channels - Kty
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TidalChannelsKhor alBazam-UAE
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Tidal, Storm or Tsunami Channel
Note Incised Surface
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Tsunami Load Drape - Kty
Note Uniform Thickness of Layer
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Clastic Sequence Stratigraphic Hierarchies
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Channels Shelves
Channel
Shelf
Both have unique processes structures that can
be used to identify their setting
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Tools Enable Sequence Stratigraphic Analysis
This analysis involves

• Subdivision of section into sequences,
  parasequences and beds.
• Link conceptual models with mix of components of
  the individual sequence, parasequence or beds
• Use these to explain the depositional setting in
  terms of their lithology, grain size, sedimentary
  structures, contacts character (gradational,
  abrupt) etc

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SequenceStratigraphicAnalysis
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Unconfined Flow - Not in a Channel

• Unique Processes
• Flow is in all directions
• No lateral boundaries, only upper and lower
  boundaries
• Velocity changes high to low
• Sediment responses
• Decrease in grain size Fining outward (coarse
  to fine)
• Erosional/sharp/gradational contacts
• Accretion Downstream, upstream and vertical
• Decrease in sedimentary structures away from
  source
• Geometries
• Sheets
• Thin in direction of flow

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End of the Lecture

• Can it be supper time?