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WAVELET TRANSFORMATION TOOL PLUG-IN FOR PETREL USERS’ GUIDE

SCHLUMBERGER INFORMATION SOLUTIONS

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ABOUT THIS DOCUMENT

This document provides instructions for the use of the Wavelet Transformation Tool plug-in for Petrel. It also provides instructions to operate the plug-in.

COPYRIGHT NOTICES AND DISCLAIMERS

Wavelet Transformation Tool for Petrel, Copyright © Schlumberger. All rights reserved.

No part of this user documentation may be reproduced, stored in a retrieval system, or translated in any form or by any means, electronic or mechanical, including photocopying and recording, without prior written permission of Schlumberger Information Solutions, 5599 San Felipe, Suite 100, Houston, TX. 77056-2722.

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Contents

1. Overview ..........................................................................................................................................................4

1.1 Location of Wavelet Transformation Tool process ...................................................................................4

1.2 The process dialog .....................................................................................................................................5

1.3 Folder structure ..........................................................................................................................................7

2. Tutorial: Creating a Decomposed Seismic Cube .............................................................................................9

3. Help and support information ...................................................................................................................... 13

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User Manual

1. Overview

The "Wavelet Transformation Tool" plug-in (Version: 1.0.0) for Petrel 2010 provides tools for

spectral decomposition of seismic data by Continuous Wavelet Transform (CWT) or Short Time

Fourier Transform (STFT).

Spectral analysis is an important signal processing tool for seismic data. The transformation of a

seismogram into the frequency domain is the basis for a significant number of processing algorithms

and interpretive methods. However, for seismograms whose frequency content varies with time, a

simple 1-D (Fourier) frequency transformation is not sufficient. Improved spectral decomposition in

frequency-time (FT) space is provided by the sliding window (short time) Fourier transform,

although this method suffers from the time frequency resolution limitation. Recently developed

transforms, based on the new mathematical field of wavelet analysis, bypass this resolution

limitation and offer superior spectral decomposition. The continuous wavelet transform with its

scale-translation plane is conceptually best understood when contrasted to a Short Time Fourier

Transform.

Wavelet transform has become a widely adopted interpretation tool for reservoir description and has

been used in seismic data analysis and attribute extraction. With wavelet transform, the distribution

of the lithology can be identified based on 3D seismic data, and hence well placement can be further

optimized. By cutting a slice with certain frequency along the target layer, the lithology distribution

with corresponding thickness can be obtained. Repeating this for frequency scanning, we can get

distribution of different thickness. In this process, proper decomposition method is critical.

Compared with other methods, it has explicit physical meaning and can match the signal to be

analyzed furthest. So it is optimal selection for both signal noise separation and high frequency

depict.

The "Wavelet Transformation Tool" plug-in allows the user to perform spectral decomposition by

six different algorithms. These are divided in two broad categories, Continuous Wavelet Transform

(CWT) and Short Time Fourier Transform (STFT).

Under CWT group, user has the option of choosing Morlet, Ricker, or Haar wavelets. These

different wavelets have different properties that may be suited for different data and different

frequencies. Similarly, for STFT, user has the options of selecting Rectangular, Hanning or Gaussian

window.

1.1 Location of Wavelet Transformation Tool process

The Wavelet Transformation Tool process is launched by double-clicking on the process under the

Petrel’s "Processes" tab under the "Geophysics" heading (Figure 1).

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Figure 1: Wavelet Transformation Tool

1.2 The process dialog

The "Wavelet Transformation Tool" process creates decomposed results folder in the Input pane of

main petrel window, where settings of the process are stored.

To create a decomposed 3D cube, inline/xline or 2D line, following steps should be performed:

1. Input the 3D cube, inline/xline or 2D line which needs to be decomposed.

2. Choose the Method type. User can select CWT for Continuous Wavelet Transform and STFT

for Short Time Fourier Transform.

3. Set the frequency value, since both the transform will need a unique frequency (range: 1-125

Hz) around the zone of interest, over which the algorithm of wavelet transform will be

performed.

4. If CWT is selected as method type then Wavelet dropdown gets enabled. User can select

either of Morlet, Ricker and Haar as a type to perform Wavelet transform using Continuous

Wavelet Transform. If STFT is selected as method type then Window dropdown gets enabled

and user can select either of Rectangular, Hanning or Gaussian windows to perform Short

Time Fourier Transform.

5. If users need to realize the resultant output, they can check the Realize option and select the

folder where they want to export the output in SEGY and/or ZGY (Only for 3D cube) format.

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The "Wavelet Transformation Tool" process dialog is shown on the Figure 2.

Figure 2: Wavelet Transformation Tool process dialog.

The plug-in dialog contains three main sections:

1. Input section

The input section contains button, to provide the Seismic 2D Line, Inline/Xline or 3D

Cube.

2. Parameters section

The parameters section allows defining the parameters for the decomposition. Plug-in

implement wavelet transform technique using Continuous Wavelet Transform method or

Short Time Fourier Transform method.

User will provide information about the frequency value around the zone of interest over

which the algorithm of spectral decomposition will be performed. In case of CWT, Morlet

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wavelet is suited for all frequencies but produces poor time resolution at lower frequencies,

whereas Ricker wavelet has shown to produce better result with seismic data at lower

frequencies.

Similarly the user has the option of choosing different window function for Fourier

Transform (STFT) namely “Rectangular Window”, “Hanning Window” and “Gaussian Hill".

These may produce slight variation in the result which user may wish to see.

3. Output section

The output section facilitates to export the results in two different formats- SEGY and ZGY.

User can check the “Realize” option which will enable other two (SEGY and/or ZGY)

checkboxes and user can browse to the file path where the output can be saved. Seismic 3D

cube can be saved in both formats at a time, whereas inline, xline or 2D line can be saved in

SEGY format only.

The command bar of the process dialog window contains the following buttons:

Apply (or ALT+A) – Perform decomposition and save the decomposed results in the Input

pane of Petrel.

Ok (or ALT+O) – Perform decomposition, save the template and close the plug-in UI.

Cancel (or ALT+C) – Close the plug-in, no saving unless Apply button is used previously.

1.3 Folder structure

The result of the wavelet transformation is added to the survey collection which is named as

"Wavelet Transformation Results". In this survey collection, 3 seismic collections are added namely,

SeisemicCubeSpectrogram, Seismic2DLineSpectrograms and InlineOrXline Spectrograms, when

corresponding spectrograms are generated by the user.

Structure of seismic collection spectrograms is explained below:

1) SeismicCubeSpectrograms : When wavelet transformation is performed on a seismic cube, the

resultant cube of the spectrogram is added to the this seismic collection. Under this collection

another seismic collection by the name of the seismic cube is added.

For example, if the user has selected a seismic cube named "Test" then the Seismic collection will

be named Test. Under this new seismic collection, the spectrogram is added as a seismic cube with

naming convention as,

"Freq" << Frequency>>_<<Transform method>>_<<window/wavelet>>

"Frequency" is the frequency provided as input at which Spectral Decomposition is performed,

"Transform method" is the process viz. CWT or STFT and "window/wavelet" is the type of wavelet

viz. Morlet, Ricker or Haar; or type of window viz. Rectangular, Hanning or Gaussian.

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Ex. "Freq30_CWT_Morlet" means the result is for 30 Hz, CWT and Morlet Wavelet.

2) 2DLineSpectrograms: When wavelet transformation is performed on a seismic 2D line, the

resultant 2DLineSpectrogram is added to this seismic collection. Under this seismic

collection, a seismic line 2D collection by the name of the seismic 2D line over which the wavelet

transformation is performed is added. Under this seismic line 2D collection the spectrogram is added

with file name convention as,

"Freq"_<< Frequency>>_<<Transform method>>_<<window/wavelet>>

"Frequency" is the frequency at which wavelet transformation is performed, "Transform method" is

the process viz. CWT or STFT and "Method" is the type of wavelet viz. Morlet, Ricker or Haar; or

type of window viz. Rectangular, Hanning or Gaussian.

Ex. Freq45_STFT_Hanning means the result is for 45 Hz, STFT and Hanning Window.

3) InlineOrXlineSpectrograms: When wavelet transformation is performed on an inline or xline of

a seismic cube, the resultant inline/xline spectrogram is added to this seismic collection. Under

this seismic collection another collection by the name of the parent seismic cube of the inline/xline is

added. Under this, two more new seismic collections by the name inlines and/or xlines are present,

which contain the results for the corresponding inline or xline data respectively.

Under the collections inlines or xlines, the 2D spectrogram is added as a seismic line 2D collection

with file name convention as,

<<Inline/Xlinename>>_"Freq" <<Frequency>>_<<Transform>>_<<wavelet/window>>

"Frequency" is the frequency at which wavelet transformation is performed, "Transform" is the

process viz. CWT or STFT and "Method" is the type of wavelet viz. Morlet, Ricker or Haar; or type

of window viz. Rectangular, Hanning or Gaussian.

Ex. Inline 113_Freq45_STFT_Hanning means the result is for Inline113, 45 Hz, STFT and Hanning

Window.

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Figure 3: Folder structure of Results

2. Tutorial: Creating a Decomposed Seismic Cube

In this tutorial we will use the "Wavelet transformation tool" process to create decomposed cube

with demo dataset. The dataset is Petrel 2010.2 project and contains a seismic survey with a seismic

cube named "Test" in it (Figure 4):

Figure 4: Input data.

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1. Open the tutorial project “Tutorial.pet”. Check availability of the input data that will be used

in the tutorial. Under the Seismic folder you will find "Test" which contains "Inline562" and

"Xline430". This cube will be used for decomposition (transformation).

2. Double click on the “Wavelet transformation tool” process in the “Processes” pane.

3. Drop the Cube “Test” from “Input” tab to the “Input” section in the dialog by selecting the

cube and clicking on button as shown in Figure 5.

Figure 5: Input cube.

4. Next we need to define parameters

Select CWT as method, which is also the default selection, by clicking on the radio button.

Select Frequency value as 15 Hz. This belongs to the zone of interest over which the

algorithm of spectral decomposition will be performed.

Select Morlet as the mother wavelet in the Wavelet dropdown box to perform Continuous

Wavelet Transform.

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Figure 6 shows all the parameters selected.

Figure 6: Define Parameters.

5. Check “Realize” option to export the results and select SEGY as desired format. In the File path

box browse to the Lab folder location on the hard drive of target machine, as shown in Figure 7.

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Figure 7: Export Output.

6. Press “Apply” button located in the bottom of the window to create new decomposed seismic

cube as shown in Figure 8. Click “OK” to save results and close window.

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Figure 8: Decomposed Seismic Cube

Now you have the decomposed cube in the input tree which can be used for interpretation of direct

hydrocarbon indicator- occurrence of low frequency shadows below the reservoir.

3. Help and support information

The "Wavelet Transformation Tool" plug-in (Version: 1.0.0) is provided by © Schlumberger. For

support information contact Schlumberger Information Solutions support on your location or write

request to the next e-mail: customercarecenter@slb.com.