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Introduce the crucial basic terminology of structural geology
1. Definitions and Terminology
MSc REM Reservoir Structure ½ ModuleDefinitions and
Terminology
Sergei Parnachov
Gary D. Couples
Helen Lewis
2. This Lecture
MSc REM Reservoir Structure ½ ModuleThis Lecture
Purpose: Introduce the crucial basic
terminology of Structural Geology
Outline:
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Orientation of planes and lines
Faults
Folds
Faults/Fold relationships
Fractures
Typical Features for shortening/extention
environments
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3. Analysis Levels
MSc REM Reservoir Structure ½ ModuleAnalysis Levels
–
Kinematical
–
shape and body’s relations
motions
Geomechanical
–
stress/strain relations (incl.
ductile/brittle type of deformation)
More descriptive
Geometrical
More Interpretative
Increasing level of complexity
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4. Strike
MSc REM Reservoir Structure ½ ModuleStrike
Geographical North Pole
0/3600
Rules:
350
• always measure
clockwise,
East / 900 • may be measured
with two results with
1800 difference:
West / 2700
2150
South / 1800
350 or 2150 – both
are correct
True (Geographical) Strike Direction
(“Strike”) is: 350
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5. Line Orientation
MSc REM Reservoir Structure ½ ModuleMagnetic North Pole
Line Orientation
magnetic declination
(some 70 in West
Siberia)
350
West / 2700
2150
South / 1800
Magnetic Strike Direction is:
350-70 = 280, so correction
+70 has to be made for
compass
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6. Planes Orientation
MSc REM Reservoir Structure ½ Moduleprojection
300
Planes Orientation
200
100
Structure
Contour
Map
Contour
Lines
True for the Left-Hand
Rule.
Basically dip should
be noted: 22SW/105.
Alternatively Dip
direction (Instead of
Strike) may be noted.
Multiple
“rules”
exist…
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7. Orientation of Lines
MSc REM Reservoir Structure ½ ModuleOrientation of Lines
«plunge» = «погружение»
Again, multiple
“rules” exist…
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8. Faults
MSc REM Reservoir Structure ½ ModuleMore-or-less planar surface along which there has been
relative displacement of the two sides?
Faults
OR
Process zone (finite thickness) in which fault-rock
materials are created and altered?
(Hooper, Hatcher, 1988)
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9. Fault Names
MSc REM Reservoir Structure ½ Module• Normal Fault = «сброс»
Fault Names
• Reverse Fault = «взброс»
• Strike Slip Fault = «сдвиг»
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10. Slip Direction
MSc REM Reservoir Structure ½ ModuleStrike Slip Direction:
Slip Direction
• opposite block moves to the left: Sinistral
Strike Slip = «левосторонний сдвиг»
• opposite block moves to the right: Dextral
Strike Slip = «правосторонний сдвиг»
The rock layers
continue beyond the
ends of the drawing!
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11. Naming the Blocks
MSc REM Reservoir Structure ½ ModuleNaming the Blocks
• Hangingwall = «висячее крыло»
• Footwall = «лежачее крыло»
Old mining terms
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12. Recognizing Faults on Structural Maps
MSc REM Reservoir Structure ½ ModuleRecognizing Faults on Structural Maps
Naming the blocks and recognizing fault’ types
Kisimbay Oilfield, Western Kazakhstan (Bisengalieva et al., 2002)
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13. Anderson’ Faults Concept
MSc REM Reservoir Structure ½ Moduleσ1 ≥ σ2 ≥ σ3
σ1 is vertical,
σ2 and σ3 are
horizontal
Anderson’ Faults Concept
σ1 and σ2 are
horizontal, while
σ3 is vertical
σ1 and σ3 are
horizontal, while
σ2 is vertical
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14. Fault’s dip angle
MSc REM Reservoir Structure ½ ModuleStrain ellipse
(for reverse fault area)
Fault’s dip angle
were
φ is a internal friction angle. For
sand/sandstones within elastic
behavior φ ≈ 300 (and strongly
depends on Poisson ratio)
potential hydro
fracture orientation
Hubbert & Willis, 1957
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15. Stress Trajectory Variations
MSc REM Reservoir Structure ½ ModuleStress Trajectory Variations
Even “simple” loadings
cause stress trajectories to
curve, so the vertical stress
is not a principal stress.
And complex loadings
cause considerable spatial
(and temporal) variations
in the stress field.
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16. Fault Sets - Extension
MSc REM Reservoir Structure ½ ModuleHorst = горст
Fault Sets - Extension
Graben = грабен
Half Graben = полуграбен
Listric Fault = листрический разлом
σ1 is vertical,
σ2 and σ3 are
horizontal
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17. Fault Sets – Extension: a bit more about growing faults
MSc REM Reservoir Structure ½ ModuleFault Sets – Extension:
a bit more about growing faults
After Mitchum et al., 1990
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18. Fault Sets - Shortening
MSc REM Reservoir Structure ½ ModuleFault Sets - Shortening
Duplex Zone = дуплекс
Imbicate Fan = чешуйчатый надвиг
Detachment = детачмент
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6
5
4
3
2
1
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19. What is a fold? And Fold Names
MSc REM Reservoir Structure ½ ModuleWhat is a fold? And Fold Names
Feature where rock layers or other markers become
non-planar due to deformation
Anticlines are a
major trap type
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20. Describing Surfaces
MSc REM Reservoir Structure ½ ModuleTwiss & Moores, 1992
Describing Surfaces
Hinge
lines
Crestline and Trough line are the lines of maximum and minimum elevation respectively
Hinge Line traces points with maximum curvature (doesn’t necessary coincide with
Crest/Trough lines)
Inflection Line (i) separates adjacent folds and traces area with minimal curvature (points of
changing curvature sign)
Limb (or Flank) is low-curvature area between hinges (крыло складки)
Closure is an hight-curvature area around (or between) hinges (замок складки)
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21. Symmetry
MSc REM Reservoir Structure ½ Moduleсимметричные прямые
Symmetry
Symmetric folds (equal limb lengths)
Limbs usually have same dip
Asymmetric folds (unequal limb lengths)
наклонные (косые)
Limbs usually have different dips
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22. Multi-layers
MSc REM Reservoir Structure ½ ModuleMulti-layers
Axial surface (not always plane) connects multiple hinge lines (that is a
difference with Russian terminology)
Inflection surface include inflection lines
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23. Fold Names
MSc REM Reservoir Structure ½ ModuleFold Names
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24. Measuring Folds
MSc REM Reservoir Structure ½ ModuleMeasuring Folds
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25. Thickness changes?
MSc REM Reservoir Structure ½ ModuleThickness
changes?
Similar Folds are more
“popular” in nature: mass flow
exist from high-stress areas
(limbs) to low-stress (closures)
Isogone – line connected
points with same dip angle
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26. Causes?
MSc REM Reservoir Structure ½ ModuleCauses?
складки
продольного
изгиба
складки
поперечного
изгиба
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27. Fault-Bend Interaction: Folds
MSc REM Reservoir Structure ½ ModuleFault-Bend Interaction: Folds
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28. Detached Folds
MSc REM Reservoir Structure ½ ModuleDetached Folds
Zagros
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29. Rollover Structures
MSc REM Reservoir Structure ½ ModuleRollover Structures
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30. Rollover Structures
MSc REM Reservoir Structure ½ ModuleRollover Structures
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31. Rollover Structures
MSc REM Reservoir Structure ½ ModuleRollover Structures
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32. Rollover Structures
MSc REM Reservoir Structure ½ ModuleRollover Structures
rollover anticline: ductile scenario
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33. Rollover Structures
MSc REM Reservoir Structure ½ ModuleRollover Structures
rollover anticline: brittle scenario,
antithetic faults development
antithetic faults
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34. Rollover Structures
MSc REM Reservoir Structure ½ ModuleRollover Structures
rollover anticline: brittle + overlaid
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35. Inversion
MSc REM Reservoir Structure ½ ModuleInversion
Early: extension, with
sediments thickening
across faults
Later: shortening, reuse of previous faults
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36. Fractures
MSc REM Reservoir Structure ½ ModuleFractures
Fractures vs Faults: almost
invisible (not more then few
mm) lateral motion along
fracture surface
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37. Fractures
MSc REM Reservoir Structure ½ ModuleFractures
flattening fractures
extensional fracture
(real joint)
shear fractures
Some extension (if big enough
difference between principle stresses)
may exist producing “open” fractures
with definite aperture and spacing that,
being unfilled by secondary minerals,
increase reservoir’ permeability greatly –
as cube of joint aperture
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38. Fractured Reservoirs (joints only!)
MSc REM Reservoir Structure ½ ModuleFractured Reservoirs (joints only!)
Nelson (1992):
I – essential contribution in
reservoir’ porosity & permeability;
deplete rapidly, basically not
economic,
II – essential permeability; matrix
porosity support fluid flow to
fractures; good reserves,
III – fractures add to reservoir’
permeability, improving otherwise
poor-quality reservoir,
IV – regular matrix reservoir,
where fractures add permeability
anysotropy/compartmentalisation.
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39. Fault-Associated Fractures
MSc REM Reservoir Structure ½ ModuleFault-Associated Fractures
simple shear
what tends to be open?
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40. Fault-Associated Fractures
MSc REM Reservoir Structure ½ ModuleFault-Associated Fractures
Twiss & Moores, 1992
Fracturing associated with faults
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41. Fold-Associated Fractures
MSc REM Reservoir Structure ½ ModuleFold-Associated Fractures
Simple view
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42. Fold-Associated Fractures
MSc REM Reservoir Structure ½ ModuleFold-Associated Fractures
Types 3a, 3b
Type 1
Type 2
Scheme described by Stearns, 1968
Classification relates fractures and bedding orientation, plus
curvature, with some aspects of a “process model”
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43. Cooling
MSc REM Reservoir Structure ½ ModuleCooling
Twiss & Moores, 1992
Magmatic – both plutonic and volcanic - rocks cooling (columnar
basalts are good example)
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44. High Differential Stress
MSc REM Reservoir Structure ½ ModuleHigh Differential Stress
Fracturing because of general
strain (big enough differential
stress)
S
T
S/T ≈ 0.7…1.2
where:
S – fracture spacing,
T – bed thickness
Bekker & Gross, 1992
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45. Tectonic Uplifting
MSc REM Reservoir Structure ½ ModuleTectonic Uplifting
Fracturing because of tectonic
uplifting – sure should be
initiated by other processes (like
cooling)
Twiss & Moores, 1992
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46. Natural Hydrofracturing
MSc REM Reservoir Structure ½ ModuleNatural Hydrofracturing
Twiss & Moores, 1992
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47. Natural Hydrofracturing
MSc REM Reservoir Structure ½ ModuleNatural Hydrofracturing
Twiss & Moores, 1992
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