This document provides an overview of attributes and 3D seismic interpretation of data from the Alwyn North Field in the East of Shetland Islands. It describes loading the 3D seismic volume and viewing it in different windows. Key horizons are identified and interpreted. Faults and other geological structures like unconformities and tilted beds are interpreted. Seismic facies are characterized. Surfaces are created from horizons and smoothed. Fault surfaces are created. Maximum amplitude, RMS amplitude, and isochron maps are generated as seismic surface attributes. Variance is used as a volume attribute to identify features like channels at different time slices.

1. ATTRIBUTES & 3D SEISMIC
INTERPRETATION
MINI PROJECT
By : Nur Aliah Binti Nur Ismail
(22271)

2. CONTENTS
 Introduction
 Data Loading
 Viewing Data in 3D
 Viewing Data in Interpretation Window
 Phase and Polarity
 Amplitude Anomaly
 Horizon
 In interpretation window and its characteristics
 In 3D Window
 Seed Confidence
 Fault Interpretation
 Faults
 Other Geological Structures
 Seismic Facies Characteristics
 Surfaces
 Creating Horizon to Surfaces
 Smoothing Surfaces
Creating Fault Surfaces
 Seismic Surface Attributes
 Maximum Amplitude
 RMS Amplitude
 Isochron Map
Volume Attributes
 Variance

3. INTRODUCTION
o The data used for this project is from the Alwyn North
Field in the East of Shetland Islands, acquired in 1996.
o According to its geology, there are unconformities to be
expected from the time gaps of sediment deposition and
evidences of active tectonic activities.
o The Alwyn North Field is found to produce oil and gas
from Brent Group reservoirs and gas and condensate at
Statfjord Formation.
oThe Statfjord Formation was deposited in an alluvial, fan-
delta setting with increasing marine influence towards the
top formation.

4. DATA LOADING
To begin the project, a file with
SEG-Y seismic data with preset
parameters is imported into
the input window. The settings
of the SEG-Y Import is selected
to be in 3D with an Automatic
Line Detection Method.
Further details can be seen in
the statistics data that is
located in settings. In the
statistics data, the following
information can be obtained :
 Number of inlines &
crosslines
 Inline & Crossline intervals
 Seismic Type
 Number of samples per
trace
 Number of cells total

5.  A 3D Window is opened to view the inline, crossline
and timeslice section as a step prior to interpretation
(as seen on the picture on the right). Timeslice cross-
section is created on the z-axis.
 The SEG-Y imported data needs to be “realized” to
reduce the size of data.
VIEWING DATA IN 3D WINDOW
DATA LOADING

6. VIEWING DATA IN INTERPRETATION WINDOW
 An interpretation window is created to view the seismic
traces of the data in the selected cross section.
 In this window, the amplitude strength of the seismic trace
can be clearly seen. This aids in the interpretation of the
characteristics of the seismic traces as well as the
structural components observed.
 The seismic traces can be viewed in different forms to
enhance one’s interpretation :
1. Wiggles only
2. Bitmap only
3. Wiggles and Bitmap
Figure : The Inline cross-section
is selected to be viewed in
Interpretation window
Figure : The seismic traces are displayed in Bitmap dimension Figure : The seismic traces are showed in wiggle form
DATA LOADING

7. Phase :
The phase used on this seismic traces for reflection event picking is
Zero Phase as Zero Phase produces the most reliable data,
possessing high bandwidth. It depicts the correct position of reflector.
Polarity :
The seismic wavelets are corresponding to the American Polarity. This
is indicated by the positive amplitude on zero phase traces when
there is an increase in acoustic impedance between reflectors
PHASE & POLARITY

8. AMPLITUDE ANOMALY
 Amplitude anomaly is identified where there is
an abrupt increase in seismic amplitude.
 Referring to the seismic interpretation window
on the right, amplitude anomaly is seen from
the chaotic texture among the traces on the
middle to shallower part.
 This sudden change of amplitude and acoustic
impedance may indicate the presence of
hydrocarbon, such as gas sand.

9. Horizon Characterisitc
Horizon 1 The reflector shows high amplitude and semi-continuous pattern
with a disturbance near the middle of the horizon. The horizon
is in parallel form.
Horizon 2 The reflector shows medium to high amplitude and semi-
continuous pattern. There is a slight disturbance near the
middle of the horizon and the horizon is in parallel manner.
Horizon 3 This horizon is represented by a continuous and high amplitude
reflector. It is seen to have a sloping structure that slightly dips
downwards to the right direction.
Horizon 4 This horizon shows a high amplitude reflector that shows
continuous to semi-continuous pattern. The reflector is seen to
be reflected in a parallel manner.
Horizon 5 The reflector in this horizon appears to have strong amplitude
and shows a semi-continuous pattern. The horizon also display
a mound-like or sloping structure. It elevates in the left side of
the figure and slopes downwards on the right side of the
figure
HORIZON Horizon 1
Horizon 2
Horizon 3
Horizon 4
IN INTERPRETATION WINDOW AND ITS CHARACTERISTICS
Horizon 5
Left Right

10. HORIZON
IN 3D WINDOW
Figure : The picked Horizons viewed in
3D are showing different elevation time
as represented by the colour scheme.

11. HORIZON PICKING AND ITS CHARACTERISTICS
IN 3D WINDOW
APPLICATION OF SEED CONFIDENCE
The seed confidence of
30% is applied to
cover an optimum
number of holes on the
horizon slice.
Figure : This seismic horizon possesses holes due
to uneven surface
Figure : The holes seen previously have been
covered

12. (i) FAULTS
 The coloured lines drawn
on top of the seismic lines
are interpreted to be
faults structures.
 Faults are identified from
the breakage of the
continuous reflector or
horizon.
 Some diffraction patterns
are also indicating the
presence of faults.
 To enhance the fault
structures, the seismic
traces are viewed in
Black Grey White
display , apart from
default seismic.
 *Inline no. = 2441
Black Grey WhiteSeismic (Default)
FAULT & STRUCTURE INTERPRETATION

13. FAULT & STRUCTURE INTERPRETATION
(ii) OTHER GEOLOGICAL STRUCTURES – Bedding and Unconformity
Reflectors are seen to be, mainly
continuous, parallel to sub-parallel
from one to another. This can be an
indicator that the beds,
determined by the reflectors, are
deposited horizontally, showing
interbedded parallel beds.
The strong reflectors depict high
acoustic impedance. This
indicates that there is an
unconformity or it is indicating
the boundary of lithology
difference.
The reflectors are showing
deformation as they are no
longer aligned horizontally. As
seen on the picture, the
reflectors have become tilted.
This may be an indication that
tilted beds are present.
Reflectors are seen to show a
mound-like structure. The
sloughing structure is bounded by
high amplitude at the top reflector,
indicating that there is a lithology
difference. The sloughing structure
may be due to deformation that
the basement rock had
experienced after its deposition.

14. SEISMIC FACIES CHARACTERISTICS
Horizon 1
Horizon 2
Horizon 3
Horizon 4
Horizon 5
Facies1Facies2
Facies3
Facies4Facies5
Facies Amplitude Frequency Continuity Reflector Geometry
Facies 1 Medium to High High Semi-
continuous to
continuous
- Parallel
- Locally chaotic
Facies 2 Medium Low to
Medium
Semi-
continuous to
discontinuous
- Parallel to Sub-parallel
- Chaotic in the top and the
Facies 3 Medium Low to
Medium
Semi-
continuous to
discontinuous
- Sub-parallel
- Chaotic in the middle part
Facies 4 Low to Medium,
with middle
reflector having
high amplitude
Low Discontinuous - Sub-parallel
- Chaotic
Facies 5 Medium to High Medium to
High
Semi-
continuous to
disontinuous.
- Sub-parallel reflectors are
titled. Some are chaotic.
- Indentation of reflection
near predicted faults
- Onlapping feature of
sediments (on the right)

15. SURFACES
 Horizon and Surface are two different things. Surfaces are generated in a flat, regular 2D grid. Meanwhile, Horizon is
held in the 3D grid.
 Selecting Make/Edit Surface tool is the ideal tool to grid all types of data, as Horizons will involve more complex
operations due to its 3D model.
 For this project, the geometry of the grid size and position are put to be Automatic. The input for the surface is the
targeted horizon. These surfaces are also named respectively in an ascending order, moving from top to bottom.

16. HORIZON SURFACE
CREATING HORIZON TO SURFACE - OUTPUT
SURFACES

17. Before Surface Smoothing :
Figure : shows the generation of the 5th Surface
produced after the horizon slice has been applied
with seed confidence of about 30%.
SMOOTHING SURFACES
SURFACES

18. After Surface Smoothing :
Figure (left) : shows the generation of the 5th Surface
that has been smoothed using the “Smooth” function in
Surface Operations, with the iteration and filter width
of 1.
SMOOTHING SURFACES
SURFACES

19. Figure : Shows the fault lines that are
picked in every 100 m interval Figure : The fault surface, namely, Fault
Surface 2, is produced using the Make/edit
surface tool
Figure : Shows Fault line
interpretation 2 is added as an
input to Make/Edit Surface tool in
Automatic grid size and position
Fault Interpretation 2
Fault Interpretation 2
Fault Surface 2
CREATING FAULT SURFACES
SURFACES

20. SEISMIC SURFACE ATTRIBUTES
(I) MAXIMUM AMPLITUDE
Figure : Once the input seismic data is
added, it is important to define the
reference horizon and the surface
before applying the surface attribute
Figure : The map view of Surface 4 where
Maximum Amplitude surface attribute is applied

21. SEISMIC SURFACE ATTRIBUTES
(I) MAXIMUM AMPLITUDE
Figure : The map view of Surface 4 where
Maximum Amplitude surface attribute is applied
 Maximum Amplitude is measured from analyzing amplitude
anomalies. The dominant features were identified on the
basis of amplitude variation across the area.
 As seen in the figure, low and high amplitude events are
displayed accordingly to the color scheme.
 This surface shows mainly medium to high value in the left
side and some part in the middle, indicated by greenish
yellowish colour. Blue colour indicates lower value, which
means that it has lower amplitude variation.
 The greenish yellowish part of the figure may indicate bright
spots due to potential gas accumulations as gas will produce
changes in amplitude.
 Presence of channel deposits can also produce variation in
amplitude
 By using this seismic attribute, one can identify the areas
which have high or low amplitude variation, prior to the
process of interpretation.

22. SEISMIC SURFACE ATTRIBUTES
(II) RMS AMPLITUDE
Figure : The map view of Surface 5 where RMS
Amplitude surface attribute is applied

23. SEISMIC SURFACE ATTRIBUTES
(II) RMS AMPLITUDE
 Root mean square (RMS) attribute, also referred to as the
quadratic mean, measures the amplitude response over a seismic
dataset
 RMS attribute places an emphasis on the variation in acoustic
impedance over sample intervals and enhances anomalies or
isolated features within the interpreted horizons by the use of
amplitude response. Hence it aids interpretation.
 In the figure shows that there is high rms amplitude mainly at the
left side of the figure, with lower value in the middle part.
 The high RMS amplitude may indicate channel deposits or even gas
accumulation within the sediments.
Figure : The map view of Surface 5 where RMS
Amplitude surface attribute is applied

24. Isochron map is a contour map that displays the variation in time between two seismic events
or reflection. In other words, the thickness of between the surfaces can be known.
II
I
IV
III
Figure : The numbers stated represent the respective
thickness, bounded by surfaces
Figure : To create an Isochron map,
the thickness can be calculated in
Calculation Operations with a
defined base surface.
CREATING ISOCHRON MAP
ISOCHRON MAP

25. (IV) Thickness Between Surface 4 and Surface 5
Figure : The bounding surfaces (Surface 4 &
5)
 The isochron map is viewed for the
thickness between Surface 4 and
Surface 5, whereby Surface 4 is
considered flat with Surface 5
having a sloping structure.
 The colours indicate the thickness of
the map, as shown on the colour
scheme.
 As seen in the map (most right), the
thickness increases from middle
part to the right part of the map. It
is proven by the colour change from
red to yellow to green and lastly,
blue colour. This supports the sloping
down of Surface 5.
 On the left part of the map shows a
decrease in thickness where the
color goes from green to yellow to
red. This explains the sloping up of
Suface 5.
CREATING ISOCHRON MAP
ISOCHRON MAP
Surface 4
Surface 5
Figure : The Isochron Map for (IV)
Thicknesss

26. VARIANCE
VOLUME ATTRIBUTES
 Variance is the statistical measure of data or
attribute variability about the mean.
 It is a coherence attribute that is know to be
almost identical to semblance based attributes.
The variance attribute is depending on the
lateral change of amplitude.
 Variance attribute is used to identify amplitude
anomalies and measure how well each trace
fits the mean trace.
 The mean trace is zero when the traces are
similar. If the traces are identical but
amplitudes are different, there might be
variability, hence putting value in Variance.
 In this project, the characteristics of the seismic
traces are viewed at different timeslice for
further interpretation

27. VOLUME ATTRIBUTES – VARIANCE
VIEW IN TIME SLICE (-656 ms)
Figure : Channel deposits will cause a difference in the amplitude value,
hence identified by the variance attributes.
Channel

28. VOLUME ATTRIBUTES – VARIANCE
VIEW IN TIME SLICE (-1124 ms)
Figure : Display features of possibly paleochannels. The western part of
the map shows medium variance (black lines) may indicate difference in
lithology
Possible channel structure

29. VOLUME ATTRIBUTES – VARIANCE
VIEW IN TIME SLICE (-2024 ms)
Figure : Shows possible paleochannel with faint channel sides and shows
meandering attitude. The high variance (black) at most of the places seen
on the surface may be dua to lithology difference.
Possible paleochannel
Possible lithology difference

30. VOLUME ATTRIBUTES – VARIANCE
VIEW IN TIME SLICE (-2624 ms)
Figure : In this timeslice, part of the top of the mound-like structure can be
sighted. Fault lines can be seen, in black, elongated structure. Meandering
channels can also be seen as the sides of the channel is black from the
high variance value.
Fault
Part of threshold on the sloping
structure
Channel
Top of the mound-like structure

31. VOLUME ATTRIBUTES – VARIANCE
VIEW IN TIME SLICE (-2924 ms)
Figure : Timeslice at -2924ms shows a number of fault lines, seen from the
elongated and dark boundaries. The lighter part on the surface is
believed to have similar lithology since small variance is detected.
Fault
Similar
lithology