2. Sedimentology 1/2
Provide methodology for image interpretation
- Interpretation confidence.
- Image facies analysis.
- Dip picking and interpretation.
- Core calibration.
The methodology can be demonstrated in a classroom;
the rest is PRACTICE AND EXPERIENCE.
Objective
7. Sedimentology 1/7
Core versus images – complementary techniques
Advantages
Core
• Quantify lithological,
textural & mineralogical
information.
• Quantify f, K &
saturation.
• Good bed resolution.
• Detail of bedding
and/or lamination
types.
• And much more…
Images
• Larger aerial
coverage.
• Accurate orientation
information.
• Continuous regularly
sampled dataset.
• Good data on
bedding and/or
lamination continuity
8. Sedimentology 1/8
Images
• Provides little textural
information in
isolation.
• Qualitative
information on f, K &
saturation.
• Sensitive to borehole
conditions.
• How can we build
confidence?
Core versus images – complementary techniques
Disadvantages
Core
• Geometry of
sedimentary structures
often unclear.
• Often incomplete and
difficult to depth match.
• Orientation of
structures commonly
unclear.
11. Sedimentology 1/11
• Grade 1
– Features which can be categorically identified
• Grade 2
– Features which do not have a
unique interpretation
• Grade 3
– Features which are ambiguous,
i.e. probably non-geological
Image interpretation confidence
15. Sedimentology 1/15
Open hole log data.
Sedimentological
interpretation of images.
Image interpretation drag & drop
Facies interpretation
16. Sedimentology 1/16
Fabric index - determined via flash cards
Mottling and loss of fabric in this example is due to
bioturbation - hence we have a bioturbation index
Handling textures
19. Sedimentology 1/19
A Definition of ‘Lithofacies’
A sedimentary unit of distinctive
lithology and internal sedimentary
fabric .........................
21. Sedimentology 1/21
Having identified lithofacies…..
Grouped into Lithofacies
Associations which are of
environmental significance
Retrogradational or progradational stacking of
parasequence sets - these may be related to dip
variations
Grouped into Lithofacies Successions which
are analagous to Parasequences
Sequence Stratigraphy !
22. Sedimentology 1/22
• The images (tool gamma
ray) are depth-matched to
the OH logs (gamma ray).
• The core gamma ray is
depth matched to the image
gamma ray.
Reference curve
image log gamma ray
Match curve
core gamma ray
Core-image depth matching
• The core depth match is
“fine tuned” to match image
features.
24. Sedimentology 1/24
Interpretation of features
seen in images
Facies interpretation
Palaeotransport
Core description log
Image interpretation with core calibration
25. Sedimentology 1/25
Top 1011’
Base 1012’
Goniometry Technique
• The transparent goniometry
sleeves are matched in width to
the core circumference
• Each sleeve has a central
reference line which is matched
to the MOL
• The MOL provides an
independent reference line for
the measurement data and
ensures that features marked
on the sleeves are consistently
oriented for each core set
26. Sedimentology 1/26
Scribed core
Primary
knife
Secondar
y
knives
Data Collection
• Sedimentary and tectonic
features are traced onto the
sleeve and annotations made of
features & lithology
• Positions of primary and
secondary knives are recorded
(scribed core)
• Sleeves are unwrapped, photo-
reduced and spliced into A4-
sized image panels
• The panels are then digitised
and transferred into continuous
depth-based Terrasciences files
28. Sedimentology 1/29
Interpretability is primarily based on image
quality but can be aided by the
“local knowledge’ approach
Measuring confidence is subjective;
consistency is important.
Image interpretation confidence
29. Sedimentology 1/30
• Dips are picked on features
seen in the static (left) and
dynamic (right) images and
using the open hole logs.
• Dips are appropriately
classified.
• Facies are identified and
colours assigned in the right
hand column.
• Genetically related facies
are grouped into facies
associations and colours
are assigned in the left hand
column.
• Schemes are refined as the
interpretation continues.
Image interpretation lithofacies collation
30. Sedimentology 1/31
Dry Sandflat
Dry Sandflat
Good Good <5
Poor Poor N/A
Aeolian Dune
Aeolian Dune
<35-65
API
Good Good >15
Good Good
Button
to
Button
Pad
to
Pad
Dip
Angle
Clasts?
<15 >5
Facies
Associations
Description Environment GR
Response
High angle cross-
beds.
Axh
Axg
Al
Am
Aw
Sap
Low angle
cross-beds.
Planar
stratification.
Wavy lamination -
>20% clay
Wavy lamination -
<20% clay
Massive
Damp Sandsheet
Damp Sandflat
Moderate
to good
Poor to
moderate
Variable
low angle
Moderate
to good
Poor to
moderate
Variable
low angle
<35-65
API
<35-65
API
<40-75
API
Density
&
porosity
2.5-2.6g/cc
3%
2.5-2.6g/cc
3%
2.55-
2.7g/cc
3%
<35-90
API
2.5-2.6g/cc
3%
2.45g/cc
3-8%
No data No data
Lithofacies associations
Fluvio-aeolian succession
38. Sedimentology 1/39
1. Recognition of palaeohorizontal.
2. Determination of structural dip.
3. Structural dip removal from the dip data set.
4. Assess sediment dispersal orientations.
5. Refine dip classification scheme.
6. Repeat 4 and 5 as necessary.
Sediment dispersal methodology
39. Sedimentology 1/40
• Recognition of originally horizontal sediments
(particularly mudrocks) is key to structural and
sediment dispersal analyses (palaeotransport/
palaeoslope).
• Sediments deposited horizontally are structural
dip indicators (<20% of strata are deposited
horizontally).
• Removal of the structural dip component from
the dip data set allows for analysis of sediment
transport.
Palaeohorizontal
45. Sedimentology 1/46
Statistical local curvature techniques
Cross bed sets deposited on horizontal surface
Axis of curvature
Poles to
bedding planes
Tilting and
generation of
structural dip
Poles to bedding describe a
plane, the pole to which
(axis of curvature) is in the
plane of structural dip.
The axis of curvature
of multiple, variably
oriented bed sets
define the structural dip.
Structural dip.
47. Sedimentology 1/48
Axial Trend Analyses
Genetically related deformed surfaces will plot on a great
circle (with some natural scatter), and the pole (or axis) to
that great circle will define the overall trend of the
architecture (fold or slump axis).
48. Sedimentology 1/49
• Dips in the 5-15o range are critical to defining
reservoir architecture and dispersal orientations.
• Identify angular unconformities.
• Direct measurement of stratal geometry.
• Orientation of major bounding surfaces.
e.g. incised features, flooding surfaces
• Analyse changes in depositional regime and
sediment dispersal at key surfaces.
Palaeotransport interpretation
49. Sedimentology 1/50
Unimodal mode perpendicular to current.
e.g. point bar master bedding.
Bipolar azimuthal patterns in cross bedding deposited
by unidirectional currents.
small reverse azimuth spread due to antidune
cross bedding.
Bipolar cross bedding with transport axis perpendicular
to angle of repose.
e.g. seif dunes
Bipolar palaeocurrents with perpendicular mode.
e.g. turbidite erosional and slump structures.
after Selley, 1972
Palaeocurrent significance
57. Sedimentology 1/58
• In order to interpret sediment dispersal, an
appropriate conceptual depositional model is
required.
• This involves the understanding of:
• The spatial arrangement of different hierarchies
of bedding surfaces.
• The implications of these geometries for
sedimentation.
• Bedform orientation.
Bedform reconstruction
58. Sedimentology 1/59
• Identify features on the images.
• Identify sedimentary facies .
• Select the most reliable transport indicators (or
indicators) of sand body geometry.
• Remove structural dip.
• Construct azimuth histograms, vector plots etc and
reconstruct architecture if possible.
• Are the dip magnitudes and azimuth patterns typical
of these features?
• Is the azimuth scatter tolerable?
• Is there evidence for artefact data?
Palaeocurrent analysis method
65. Sedimentology 1/66
Deep water clastic systems
STRUCTURES
– slumping/soft sediment deformation
– slide/glide planes
– bed-top relief
– erosional scours/bed bases
– compactional, drape features & (rare?) internal structures
USES
– regional/local palaeoslope
– local sandbody orientation (channels)
– lithology and net:gross
PITFALLS
– palaeoslope and palaeoflow difficult to distinguish
– disturbed zones masking transport information
– often wide scatter of palaeoflow data
66. Sedimentology 1/67
Deep water systems - debris flow
Debris flow
unit with
conductive
mudrock
clasts
Static & dynamic
FMI images
69. Sedimentology 1/70
Deep water clastic sediments
Static and dynamic
UBI images of deep
marine sandstones
Non-planar feature -
this represents
sandstone remobilised
during dewatering
73. Sedimentology 1/74
Deltaic systems
STRUCTURES
– distributary channels - similar to fluvial
– small scale structures in interdistributaries
– range of structures & orientations in delta-top facies
(wave/tide influence)
– compactional structures potentially useful
USES
– delta front dip profiles may indicate progradational direction
– palaeocurrent patterns give clues to basinal regime
(waves, storms, tides)
– delta-top sandstone architecture
PITFALLS
– regional significance of palaeocurrent data from distributary
channels questionable
– rapid lateral changes in some delta systems
– soft sed. deformation may obliterate some structures
74. Sedimentology 1/75
Deltaic sediments
Static UBI image illustrating
deltaic sediments
The dark bands represent
coal horizons
Note the dramatic drop in
the density (red) and
porosity (blue) curves
75. Sedimentology 1/76
Deltaic sediments
Static UBI image
illustrating deltaic
sediments
Marine mudstones
appear laminated
in core, but are
difficult to distinguish
on the images
78. Sedimentology 1/79
Marine clastic systems
STRUCTURES
– cross stratification (variable orientation)
– low angle lamination (0-10o)
– bimodal/bipolar foresets (tidal)
– hummocky cross-stratification
– mud drape/reactivation surfaces (tidal)
USES
– palaeogeography/basinal regime
– shoreline trend and transport direction
– evidence for tidal influence
– orientation of tidal shoals and shelf sand ridges
PITFALLS
– orientation of cross-stratification highly variable
– data from a single well not taken in isolation
– disruption due to bioturbation
83. Sedimentology 1/84
Marine clastic sediments
UBI images of
marine
sandstones
Note
development of
large-scale
vuggy porosity
within carbonate
cemented sands
87. Sedimentology 1/88
• Identify features on the images.
• Identify sedimentary facies .
• Select the most reliable transport indicators (or
indicators) of sand body geometry.
• Remove structural dip.
• Construct azimuth histograms, vector plots etc and
reconstruct architecture if possible.
• Are the dip magnitudes and azimuth patterns typical
of these features?
• Is the azimuth scatter tolerable?
• Is there evidence for artefact data?
Palaeocurrent analysis method
