Seismic_Interpretation_ppt.ppt

1. SUBSURFACE MAPPING
TECHNIQUES
Topik Kedua :
DR.rer.nat Awali Priyono
Program Studi Geofisika
INSTITUT TEKNOLOGI BANDUNG
2006

2. Seismic Interpretation Step
• Seismic picking
• Fault interpretation
• Contouring
• Time structure map
• Velocity modeling
• Depth conversion
• ----------------------------------------------
• Hydrocarbon indicator
• Stratigraphic modeling
• Pitfalls in interpretation
• The search for sandstone reservoir
• The search for carbonate reservoir

3. Basic Seismic Mapping
• This is no longer done by hand,
but via the use high-powered
interpretative or graphic
workstations that rapidly access
huge volumes of 2D & 3D
seismic data

4. Synthetic seismogram, with geologic marker, sonic log,
wavelet, and surface seismic

5. Seismic Well Tie and Tracing

6. Seismic Structural Interpretation

7. 3D Visualization
• ‘Slice & Dice’ the 3D
seismic volume in a
variety of different
orientations
–in-line, cross-line and
time slices
–horizon and fault
slices
• Co-visualization of
multiple seismic attributes
–multi-volume
rendering and analysis
• Increasing use of auto-
tracking technologies and
smart ‘applets’ the
recognize geological
features

8. Subsurface Structure Mapping
Real Normal Fault Network
Resulting 3D
Structural Model
Structure Contour Map
Derived from 3D Model

9. Coherency
• Quantitative measure of the lateral
continuity of seismic events
• Actively enhances the imaging of
small discontinuities such as
faults, fractures, or channel
margins at or close to the limit of
seismic resolution
–such features would be more or
less impossible to map using
traditional manual picking
techniques
• Excellent for defining lateral extent
of and linkage within fault networks

10. Fault Recognition
• Detection limit
ability to resolve difference
between adjacent seismic
traces function of TWT
sample size, signal:noise ratio
of data.
interpretation can be assisted
by seismic coherence or other
edge detection enhancement
attributes.
• Thin bed Resolution limit
ultimate control on contrasts
in seismic character in
stratigraphy on either side of
fault (1/4 dominant
wavelength)

11. Time Structure Map

12. Depth Structure Map
• Well reservoir picking
• Seismic to well tie
• Seismic horizon picking
• Time structure map
• Depth structure map
Depth Structure + Hc Contact Bulk Volume
Crucial step  Velocity model

13. Depth Structure Map

14. Time and Depth Migration
Zero offset section Time migration Depth migration

15. Seismic Pull-Up
• Horizon effects adjacent to
fault surface
footwall drag folding or fault
“shadow” ray path are artifacts from
seismic time migration
normal fault, low velocity layer
normal fault, high velocity layer
fault propagation fold
( after Trinchero, 2000 )

16. Seismic Sequence Analysis
The procedure of picking unconformities and correlative
conformities on seismic sections so as to separate out
the packages involved with different time depositional
units

18. Unconformities
Sequences are terminated by unconformities or a concordant

19. Onlap

20. Seismic Facies-Analysis
Aim:
Analysis of the character of the eflections
amplitude, continuity, continuity and configuration)
inside a seismic sequence to predict the depositional
environment

21. Reflection patterns on seismic sections
Internal Structures

22. Sigmoidal Sequence

23. Hummocky Sequence

24. Seismic Patern that Indicate
Sealevel Changes

25. Three-Dimensional Shapes of Seismic
Facies Units

26. Depth Slice

27. Geological Interpretation

30. Hydrocarbon Indicator
Reflection coefficients
depend on
Velocity and density of sedimentary rocks
depend on
Porosity and pore-filling fluids

31. Anomalies that could be associated with
hydrocarbon accumulations under some
conditions
• Bright spot:
Overlying rock has higher velocity than brine filled reservoir rock, lowering
the reservoir rock velocity by filling it with hydrocarbon increases the
contrast and increases the amplitude
• Dim spot:
Overlying rock has lower velocity than brine filled reservoir rock, filling it with
hydrocarbon decreases the contrast and decreases the amplitude
• Flat spot:
Where a well-defined fluid contact is present (gas-oil or gas-water) the
contrast may be great enough to give a fairly strong reflection that may
stand out because of its flat attitute
• Polarity reversal
Where the overlying rock has a velocity slightly smaller than that for the
reservoir rock, lowering the reservoir rock velocity by hydrocarbons may
invert the sign of the reflection, producing a polarity reversal

33. Dim Spot
Dim spot associated with gas accumulation in porous carbonates overlain by shales.

34. Stacked Hydrocarbon Accumulation
High amplitudes (bright spots)
&
Flat spots
&
Polarity reversals

35. Resolution
Resolution refers to the minimum separation between two features such
that we can tell that there are two features rather than only one.
Comparison between the wavelength of a 30-Hz Signal, Big Ben and a Log of a drilling.

36. Vertical Resolution
Vertical resolution means: How thick must a layer be, to discern the top
and bottom of the specific layer. Theoretically, a layer can be
distinguished when it has a thickness of ¼ wavelength
(Rayleigh-Criterium).

37. Resolution of Two Boundaries Depends on
Wavelength
Decreasing image separation

38. Horizontal Resolution