Tools for subsurface analysis

GEOL 553 Lecture 3; Subsurface
Analysis
GEOL 553:GEOL 553: Marine SedimentsMarine Sediments
University of South CarolinaUniversity of South Carolina
Fall 2005Fall 2005
Professor Chris KendallProfessor Chris Kendall
EWS 304EWS 304
kendall@sc.edukendall@sc.edu
777.2410777.2410
The Tools of Subsurface AnalysiThe Tools of Subsurface Analysi

Analysis
The Tools of Subsurface AnalysisThe Tools of Subsurface Analysis
 Well logsWell logs
 CoresCores
 SeismicSeismic
 Gravity & magneticsGravity & magnetics
Facies analysis of subsurface dataFacies analysis of subsurface data
depends on tools which delimit ofdepends on tools which delimit of
surfaces and provide clues as to thesurfaces and provide clues as to the
sediments they contain:sediments they contain:

Analysis
Well Logs Versus SeismicWell Logs Versus Seismic
Great vertical resolutionGreat vertical resolution
Delimit bounding surfacesDelimit bounding surfaces
Establish lithology of sediments penetratedEstablish lithology of sediments penetrated
 SeismicSeismic
Great lateral continuity and resolutionGreat lateral continuity and resolution
Define gross sediment geometryDefine gross sediment geometry

Analysis
Tools are Keys to Allostratigraphy
& Sequence Stratigraphy
 AllostratigraphyAllostratigraphy : bounding: bounding
discontinuities including erosiondiscontinuities including erosion
surfaces, marine flooding surfaces,surfaces, marine flooding surfaces,
tuffs, tempestite, and/or turbiditetuffs, tempestite, and/or turbidite
boundaries etc. as time markersboundaries etc. as time markers
 Sequence StratigraphySequence Stratigraphy : higher level: higher level
allostratigraphic model which interpretsallostratigraphic model which interprets
depositional origin of sedimentarydepositional origin of sedimentary
strata as products of "relative sea levelstrata as products of "relative sea level
changechange""

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

Analysis
Well Logs
 Resistivity LogsResistivity Logs
 Spontaneous Potential (SP) LogsSpontaneous Potential (SP) Logs
 Gamma Ray LogsGamma Ray Logs
 Neutron LogsNeutron Logs
 Density LogsDensity Logs
 Sonic (acoustic) LogsSonic (acoustic) Logs
Delimit of surfaces & identify sediments penetratedDelimit of surfaces & identify sediments penetrated

Analysis

Analysis
Resistivity Logs
 Measures resistance of flow of electricMeasures resistance of flow of electric
currentcurrent
 Is function of porosity & pore fluid in rockIs function of porosity & pore fluid in rock
 Frequently used to identify lithologyFrequently used to identify lithology
The most commonly used logs:The most commonly used logs:

Analysis
Spontaneous Potential (SP) Logs
 Measures electrical current in wellMeasures electrical current in well
 Result of salinity differences betweenResult of salinity differences between
formation water and the borehole mudformation water and the borehole mud
 Separates bed boundaries of permeableSeparates bed boundaries of permeable
sands & impermeable shales.sands & impermeable shales.
Next most common logNext most common log

Analysis
Gamma Ray Logs
 Records radioactivity of a formationRecords radioactivity of a formation
 Shales have high gamma radioactive responseShales have high gamma radioactive response
 Gamma ray logs infer grain size (and soGamma ray logs infer grain size (and so
subsequently inferred depositional energy)subsequently inferred depositional energy)
 Gamma ray logs are most commonly used logsGamma ray logs are most commonly used logs
for sequence stratigraphic analysisfor sequence stratigraphic analysis
Another common logAnother common log

AnalysisAfter Harris & Saller 1999

Analysis
Neutron Logs
 Measures porosity of formationMeasures porosity of formation
 Uses quantity of hydrogen presentUses quantity of hydrogen present
 Measures lithology when used with DensityMeasures lithology when used with Density
LogLog

Analysis
Density Logs
 Measures formation’s bulk densityMeasures formation’s bulk density
 Used as a porosity measureUsed as a porosity measure
 Differentiates lithologies with Neutron LogDifferentiates lithologies with Neutron Log
 Used with Sonic Logs to generate syntheticUsed with Sonic Logs to generate synthetic
seismic traces to match to seismic linesseismic traces to match to seismic lines
A common logA common log

Analysis
Sonic (Acoustic) Logs
 Measures of speed of sound in formationMeasures of speed of sound in formation
 Tied to porosity and lithologyTied to porosity and lithology
 Used with Density Logs to generateUsed with Density Logs to generate
Synthetic Seismic traces to match toSynthetic Seismic traces to match to
Seismic linesSeismic lines

Analysis
Seismic
 Define geometries of genetic reflectionDefine geometries of genetic reflection
packages that envelope seismic sequencespackages that envelope seismic sequences
and systems tractsand systems tracts
 Identify bounding discontinuities on basisIdentify bounding discontinuities on basis
of reflection termination patterns andof reflection termination patterns and
continuitycontinuity
Seismic stratigraphic interpretationSeismic stratigraphic interpretation
used to:used to:

Analysis
Seismic Boundaries
 Toplap terminationToplap termination
 Truncation of sediment surfaceTruncation of sediment surface
 Often channel bottomOften channel bottom
Termination below discontinuity, orTermination below discontinuity, or
upper sequence boundaryupper sequence boundary ::
 Onlap over surfaceOnlap over surface
 Downlap surfaceDownlap surface
Above a discontinuity defining lowerAbove a discontinuity defining lower
sequence boundary:sequence boundary:

Analysis
Seismic Boundaries
Below Boundary - Toplap terminationBelow Boundary - Toplap termination

Analysis
Seismic Boundaries
Below Boundary -Below Boundary - Truncation of surfaceTruncation of surface

Analysis
Seismic Boundaries
ChanneledChanneled
SurfaceSurface
–– BelowBelow
BoundaryBoundary

Analysis
Seismic Boundaries
Over Boundary - Onlap onto surfaceOver Boundary - Onlap onto surface

Analysis
Seismic Boundaries
Over Boundary- Downlap onto surfaceOver Boundary- Downlap onto surface

Analysis
Sequence Stratigraphy
 Surfaces of erosion & non-deposition (sequenceSurfaces of erosion & non-deposition (sequence
boundaries)boundaries)
 Flooding (trangressive surfaces [TS] &/orFlooding (trangressive surfaces [TS] &/or
maximum flooding surfaces [mfs]) & high standmaximum flooding surfaces [mfs]) & high stand
condensed surfacescondensed surfaces
Subdivision & interpretation of sedimentarySubdivision & interpretation of sedimentary
record using a framework surfaces seen inrecord using a framework surfaces seen in
outcrops,outcrops, well logs, & 2-D and 3-D seismicwell logs, & 2-D and 3-D seismic..
Include:Include:
This framework used to predict the extentThis framework used to predict the extent
of sedimentary facies geometry, lithologicof sedimentary facies geometry, lithologic
character, grain size, sorting & reservoircharacter, grain size, sorting & reservoir
qualityquality

Analysis
Tools Define Bounding Surfaces
 Relative time framework forRelative time framework for
sedimentary successionsedimentary succession
 Better understanding of inter-Better understanding of inter-
relationship of depositional settings &relationship of depositional settings &
their lateral correlationtheir lateral correlation
These surfaces subdivide sedimentary rockThese surfaces subdivide sedimentary rock &
provide:-provide:-
Conceptual models follow that link the
processes that formed the sediments and
enable the prediction of their gross geometries

Analysis
 Sequence geometries are subdivided andSequence geometries are subdivided and
defined bydefined by
Maximum Flooding Surfaces (mfs)Maximum Flooding Surfaces (mfs)
Transgressive Surfaces (TS)Transgressive Surfaces (TS)
Sequence Boundaries (SB)Sequence Boundaries (SB)
 Define how vertical succession or stackingDefine how vertical succession or stacking
patterns of unconfined sheets are arrangedpatterns of unconfined sheets are arranged
Prograde (step seaward)Prograde (step seaward)
Retrograde (step landward)Retrograde (step landward)
Aggrade (build vertically)Aggrade (build vertically)
 Sheets and unconfined lobes may containSheets and unconfined lobes may contain
Non-amalgamated bodiesNon-amalgamated bodies
 Amalgamated, multi-storied bodiesAmalgamated, multi-storied bodies
Incised topographic fill of valleysIncised topographic fill of valleys
Unconfined but localized lobes from point &Unconfined but localized lobes from point &
Hierarchy of Geometries

Analysis
Ebb Ooid Delta - UAE

Analysis
Delta Mouth Bar - Kentucky
Note Incised SurfaceNote Incised Surface

Analysis
Channel – Gulf Coast

Analysis
Flood Deltas & Channels - Kty

Analysis
Tidal
Channels
Khor
al
Bazam
-
UAE

Analysis
Tidal, Storm or Tsunami Channel

Analysis
Tsunami Load & Drape - Kty
Note Uniform Thickness of LayerNote Uniform Thickness of Layer

Analysis
Clastic Sequence Stratigraphic Hierarchies

Analysis
Channels & Shelves
Channel
Channel
Shelf
Shelf
Both have unique processes &Both have unique processes &
structures that can be used tostructures that can be used to
identify their settingidentify their setting

Analysis
Tools Enable Sequence Stratigraphic
Analysis
 Subdivision of section into sequences,Subdivision of section into sequences,
parasequences and beds.parasequences and beds.
 Link conceptual models with mix ofLink conceptual models with mix of
components of the individual sequence,components of the individual sequence,
parasequence or bedsparasequence or beds
 Use these to explain the depositionalUse these to explain the depositional
setting in terms of their lithology, grainsetting in terms of their lithology, grain
size, sedimentary structures, contactssize, sedimentary structures, contacts
character (gradational, abrupt) etccharacter (gradational, abrupt) etc
This analysis involvesThis analysis involves

Analysis
Sequence
Stratigraphic
Analysis

End of the Lecture
Can it be supperCan it be supper
time?time?

Analysis
Unconfined Flow - Not in a Channel
 Unique ProcessesUnique Processes
Flow is in all directionsFlow is in all directions
No lateral boundaries, only upper and lowerNo lateral boundaries, only upper and lower
boundariesboundaries
Velocity changes: high to lowVelocity changes: high to low
 Sediment responsesSediment responses
Decrease in grain size: Fining outwardDecrease in grain size: Fining outward
(coarse to fine)(coarse to fine)
Erosional/sharp/gradational contactsErosional/sharp/gradational contacts
Accretion: Downstream, upstream andAccretion: Downstream, upstream and
verticalvertical
Decrease in sedimentary structures awayDecrease in sedimentary structures away
from sourcefrom source
 GeometriesGeometries

Tools for subsurface analysis

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