GEOL 553: Marine Sediments
University of South Carolina
Fall 2005
The Tools of Subsurface Analysis
Professor Chris Kendall
EWS 304
kendall@sc.edu
777.2410
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
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"
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
Well Logs
Delimit of surfaces & identify sediments penetrated
 Resistivity Logs
 Spontaneous Potential (SP) Logs
 Gamma Ray Logs
 Neutron Logs
 Density Logs
 Sonic (acoustic) Logs
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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.
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
GEOL
553&Lecture
3; Subsurface Analysis
After
Harris
Saller 1999
Neutron Logs
Another common log
 Measures porosity of formation
 Uses quantity of hydrogen present
 Measures lithology when used with Density
Log
GEOL 553 Lecture 3; Subsurface Analysis
Density Logs
A common log
 Measures formation’s 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
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
Seismic Boundaries
Below Boundary - Toplap termination
GEOL 553 Lecture 3; Subsurface Analysis
Seismic Boundaries
Below Boundary - Truncation of surface
GEOL 553 Lecture 3; Subsurface Analysis
Seismic Boundaries
Channeled
Surface
– Below
Boundary
GEOL 553 Lecture 3; Subsurface Analysis
Seismic Boundaries
Over Boundary - Onlap onto surface
GEOL 553 Lecture 3; Subsurface Analysis
Seismic Boundaries
Over Boundary- Downlap onto surface
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis
Ebb Ooid Delta - UAE
GEOL 553 Lecture 3; Subsurface Analysis
Delta Mouth Bar - Kentucky
Note Incised Surface
GEOL 553 Lecture 3; Subsurface Analysis
Channel – Gulf Coast
Note Incised Surface
GEOL 553 Lecture 3; Subsurface Analysis
Flood Deltas & Channels - Kty
GEOL 553 Lecture 3; Subsurface Analysis
Tidal
Channels
Khor
al
Bazam
UAE
GEOL 553 Lecture 3; Subsurface Analysis
Tidal, Storm or Tsunami Channel
Note Incised Surface
GEOL 553 Lecture 3; Subsurface Analysis
Tsunami Load & Drape - Kty
Note Uniform Thickness of Layer
GEOL 553 Lecture 3; Subsurface Analysis
Clastic Sequence Stratigraphic Hierarchies
GEOL 553 Lecture 3; Subsurface Analysis
Channels & Shelves
Both have unique processes &
structures that can be used to
identify their setting
GEOL 553 Lecture 3; Subsurface Analysis
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

GEOL 553 Lecture 3; Subsurface Analysis
Sequence
Stratigraphic
Analysis
GEOL 553 Lecture 3; Subsurface Analysis
End of the Lecture
Can it be supper time?
GEOL 553 Lecture 3; Subsurface Analysis
GEOL 553 Lecture 3; Subsurface Analysis
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
GEOL 553 Lecture 3; Subsurface Analysis