The document discusses the tools used for subsurface analysis in geology, including well logs, cores, seismic data, and gravity and magnetic surveys. It focuses on well logs and seismic data. Well logs provide high vertical resolution and help delimit bounding surfaces and establish lithology. Seismic data provide high lateral continuity and resolution to define sediment geometries. Together these tools are used for allostratigraphy and sequence stratigraphy by identifying bounding discontinuities and sequences reflecting changes in relative sea level.
1. 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
2. GEOL 553 Lecture 3; Subsurface
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:
3. GEOL 553 Lecture 3; Subsurface
Analysis
Well Logs Versus SeismicWell Logs Versus Seismic
Well logsWell logs
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
4. GEOL 553 Lecture 3; Subsurface
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""
5. GEOL 553 Lecture 3; Subsurface
Analysis
The Tools of Subsurface Analysis
Well logsWell logs
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:
6. GEOL 553 Lecture 3; Subsurface
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
9. GEOL 553 Lecture 3; Subsurface
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:
11. GEOL 553 Lecture 3; Subsurface
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
13. GEOL 553 Lecture 3; Subsurface
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
17. GEOL 553 Lecture 3; Subsurface
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
Another common logAnother common log
18. GEOL 553 Lecture 3; Subsurface
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
19. GEOL 553 Lecture 3; Subsurface
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
Another common logAnother common log
22. GEOL 553 Lecture 3; Subsurface
Analysis
The Tools of Subsurface Analysis
Well logsWell logs
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:
23. GEOL 553 Lecture 3; Subsurface
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:
24. GEOL 553 Lecture 3; Subsurface
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:
34. GEOL 553 Lecture 3; Subsurface
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
35. GEOL 553 Lecture 3; Subsurface
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
36. GEOL 553 Lecture 3; Subsurface
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
38. GEOL 553 Lecture 3; Subsurface
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
40. GEOL 553 Lecture 3; Subsurface
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
42. GEOL 553 Lecture 3; Subsurface
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
44. GEOL 553 Lecture 3; Subsurface
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
53. GEOL 553 Lecture 3; Subsurface
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
54. GEOL 553 Lecture 3; Subsurface
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
59. GEOL 553 Lecture 3; Subsurface
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