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Seismic Reflection Data: what it is, how it can be used, & an application at Elk Hills, CA. - Hudec and Martin, 2004. Seismic Reflection Data: Definition. Seismic Reflection. return of a wave from a surface that it strikes into the medium through which it has traveled. - PowerPoint PPT Presentation
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Seismic Reflection Data:
what it is, how it can be used, & an application at Elk Hills, CA
- Hudec and Martin, 2004
Seismic Reflection Data: Definition
Records seismic waves at the surface that are reflected off of subsurface stratigraphic interfaces
Seismic Reflection
subject to or caused by an earth vibration
return of a wave from a surface that it
strikes into the medium through
which it has traveled
Images the subsurface using acoustic methods
- Clay, 1990
- Kansas Geological Survey
reflection patterns are described by
Snell's Law
Seismic Reflection Data: Acquisition
• Source• Receivers
cross lin
es
inlines
Spacing
12.5 m for Wytch Farm Oil Field16.7 m for Elk Hills Oil Field
grid of receivers for 3D survey:
- http://walter.kessinger.com/work/seisx_processing.html
Common Midpoint Method
Seismic Reflection Data: Processing
- Kansas Geological Survey
Seismic x-section
Seismic Reflection Data: Processing
two
-wa
y tr
ave
l t
ime
(m
s)
• interface reflects energy proportional to impedance difference
impedance = velocity x porosity
• subsurface geometries are reconstructed
• stratigraphic sections show up layered
Seismic Reflection Data: Resolution
VerticalHorizontal
Minimum separation between two features such that we can tell that there are two features rather than only one
Seismic Reflection Data: Interpretation
Cross -section
Time slice
Seismic Reflection Data: Interpretation
2D image of normal faults from offshore Lebanon:
http://www.mines.edu/academic/geology/faculty/btrudgil/research.html
Stratigraphic variations
Faulting on the order of 30+ meters
due to faulting
due to depositional changes
- Fort et al., 2004
Structural Applications
(Scale for this x-section)
Individual layers and faults
Stratigraphic packages and fault zones
Various scales of
interpretation
- Kattenhorn and Pollard, 2001
Seismic Reflection Data: Application
20 miles east of the San Andreas Fault
- http://rst.gsfc.nasa.gov
Elk Hills Oil Field
Part 1 of 2 step projectPart 1 of 2 step project
Ultimate goal:Ultimate goal: fracture (stress) prediction across fracture (stress) prediction across a specified stratigraphic layer a specified stratigraphic layer
• fracture pattern today is a composite of fracturing during each distinct slip event
• slip-induced stresses vary as faults interact • evolutionary history important!
Elastic models forward model for slip-induced
stress perturbations
Elk Hills: Motivation
Elk Hills: Motivation
Gain insight into fault Gain insight into fault geometry and timing at Elk Hillsgeometry and timing at Elk Hills
Industry:Industry: implications for hydrocarbon implications for hydrocarbon entrapment and chargeentrapment and charge
General:General: implications for evolution implications for evolution of thrust systemsof thrust systems
West EastA A’ BB’
Elk Hills: Stratigraphy
31S29R
McDonald structure
A
A’
2 mi
N
BB
’
NWS
Syn-depositional growth faulting:
- Thinning onto highs- Thickening across faults
Use sedimentary features to constrain fault movements with time of deposition of specific layers
Elk Hills: Stratigraphic Constraints
Stratigraphic Constraints on Fault Timing:
2D analysis (cross sections)
3D analysis (isochores)
Chronological fault evolution model
Elk Hills: Stratigraphic Constraints
Pseudowell thickness plots
Pseudowell analysisCalitroleum
2 mi
N
West
A
A’
MYA4-A
Wilhelm
Calitroleum
BRR
ms
A A’
A’A
SW NE
Elk Hills: Stratigraphic Constraints
Cross section analysis
Example 1: Onlap
Syn-faulting strata
Active faulting and uplift during deposition
Fault Movement Indicators
Elk Hills: Stratigraphic Constraints
Cross section analysis
Example 2: Offset beds of equal thickness
Pre-faulting strata
Fault Movement Indicators
Faulting post deposition
Elk Hills: Stratigraphic Constraints
Cross section analysis
Fault Movement Indicators
NESW
Elk Hills: Stratigraphic Constraints
Cross section analysis
Fault Movement Indicators
Offset onlap: 1. 3R>1R 2. 3R>BRR
0.5 mile
100 ms
Elk Hills: Stratigraphic Constraints
Isochore: line drawn through points of equal vertical (apparent) thickness of a unit
BRR
Calitroleum
Wilhelm
MYA4-A
McDonald
x1 x2 x3 x4 x5
1 mile
500 ms
Elk Hills: Stratigraphic Constraints
A
A’
2. Thin beds b)
c)
A A’
c) filled in paleo high (post tectonic)
b) fault below interval (syn tectonic)
1. Close contoursa) a)fault cut
interval at time (syn tectonic)
Two Signatures:
Structural high
AA
’
A A’
Elk Hills: Stratigraphic Constraints
Isochore: McDonald to Base Reef Ridge
N
0 2 4 6 km
0 1 2 miles
ft
Fault cut Structural high - active fault
Structural high - active fault
A A’
2R3R1R
5R
A
A’
2R
2R
3R 3R
1R
5R No expression - inactive fault
1R
5R
5R
1R
2R
3RMcDonald
BRR
6R
7
6R
7
Elk Hills: Stratigraphic Constraints
Conclusions from all stratigraphic analyses
- Reid, 1990
McDonald7, 2R, 3R
2R, 3R, 1R2R, 3R, 1R
2R, 3R, 1R, 5R
2R, 3R, 1R, 5R
Active faultsActive faults
fault initiations bracketed between horizons:
A A’
2R3R1R
5R
6R
west
B B’
6R 7
east
Elk Hills: Stratigraphic Constraints
Conclusions from all Analyses
Stage 1
Stage 2
Stage 3
Stage 4
WEST A A’
3R
A A’
2R3R
pre-McDonald(mid Miocene)
A A’
2R3R1R
pre-Base Reef Ridge(early Pliocene)
A A’
2R3R1R
5R
pre-Wilhlem (mid Pliocene)
pre-McDonald(mid Miocene)
Stage 1
Stage 2
EAST B B’
7
B B’
6R
pre-McDonald(mid Miocene)
Post MYA-4A(late Pliocene)
31S29R
A
A’
2 mi
N
B
B’
7
Elk Hills: Stratigraphic Constraints
Fault Geometry & Timing
input for elastic models
determine faulting related
stress perturbations
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