Seismic Reflection Data: what it is, how it can be used, & an application at Elk Hills, CA - Hudec...

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


Pseudowell thickness plots

Pseudowell analysisCalitroleum

2 mi

N

West

A

A’

MYA4-A

Wilhelm

Calitroleum

BRR

ms

A A’

A’A

SW NE


Cross section analysis

Example 1: Onlap

Syn-faulting strata

Active faulting and uplift during deposition

Fault Movement Indicators



Example 2: Offset beds of equal thickness

Pre-faulting strata


Faulting post deposition




NESW




Offset onlap: 1. 3R>1R 2. 3R>BRR

0.5 mile

100 ms


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


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’


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


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


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)


Stage 1

Stage 2

EAST B B’

7

B B’

6R


Post MYA-4A(late Pliocene)

31S29R

A

A’

2 mi

N

B

B’

7


Fault Geometry & Timing

input for elastic models

determine faulting related

stress perturbations

Seismic Reflection Data: what it is, how it can be used, & an application at Elk Hills, CA - Hudec...

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