Introduce the crucial basic terminology of structural geology

1. Definitions and Terminology

MSc REM Reservoir Structure ½ Module
Definitions and
Terminology
Sergei Parnachov
Gary D. Couples
Helen Lewis

2. This Lecture

MSc REM Reservoir Structure ½ Module
This 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 Module
Analysis 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 Module
Strike
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 Module
Magnetic 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 Module
projection
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 Module
Orientation of Lines
«plunge» = «погружение»
Again, multiple
“rules” exist…
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8. Faults

MSc REM Reservoir Structure ½ Module
More-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 Module
Strike 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 Module
Naming 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 Module
Recognizing 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 Module
σ1 ≥ 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 Module
Strain 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 Module
Stress 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 Module
Horst = 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 Module
Fault 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 Module
Fault 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 Module
What 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 Module
Twiss & 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 Module
симметричные 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 Module
Multi-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 Module
Fold Names
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24. Measuring Folds

MSc REM Reservoir Structure ½ Module
Measuring Folds
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25. Thickness changes?

MSc REM Reservoir Structure ½ Module
Thickness
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 Module
Causes?
складки
продольного
изгиба
складки
поперечного
изгиба
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27. Fault-Bend Interaction: Folds

MSc REM Reservoir Structure ½ Module
Fault-Bend Interaction: Folds
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28. Detached Folds

MSc REM Reservoir Structure ½ Module
Detached Folds
Zagros
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29. Rollover Structures

MSc REM Reservoir Structure ½ Module
Rollover Structures
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30. Rollover Structures

MSc REM Reservoir Structure ½ Module
Rollover Structures
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31. Rollover Structures

MSc REM Reservoir Structure ½ Module
Rollover Structures
31

32. Rollover Structures

MSc REM Reservoir Structure ½ Module
Rollover Structures
rollover anticline: ductile scenario
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33. Rollover Structures

MSc REM Reservoir Structure ½ Module
Rollover Structures
rollover anticline: brittle scenario,
antithetic faults development
antithetic faults
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34. Rollover Structures

MSc REM Reservoir Structure ½ Module
Rollover Structures
rollover anticline: brittle + overlaid
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35. Inversion

MSc REM Reservoir Structure ½ Module
Inversion
Early: extension, with
sediments thickening
across faults
Later: shortening, reuse of previous faults
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36. Fractures

MSc REM Reservoir Structure ½ Module
Fractures
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 Module
Fractures
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 Module
Fractured 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 Module
Fault-Associated Fractures
simple shear
what tends to be open?
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40. Fault-Associated Fractures

MSc REM Reservoir Structure ½ Module
Fault-Associated Fractures
Twiss & Moores, 1992
Fracturing associated with faults
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41. Fold-Associated Fractures

MSc REM Reservoir Structure ½ Module
Fold-Associated Fractures
Simple view
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42. Fold-Associated Fractures

MSc REM Reservoir Structure ½ Module
Fold-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 Module
Cooling
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 Module
High 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 Module
Tectonic 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 Module
Natural Hydrofracturing
Twiss & Moores, 1992
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47. Natural Hydrofracturing

MSc REM Reservoir Structure ½ Module
Natural Hydrofracturing
Twiss & Moores, 1992
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