In This Issue... The Consortium for Research in Elastic Wave Exploration Seismology

Transcription

1 CEWES NEWS Volume 17, No. 4-5 Apr-May 006 The Consortium for esearch in Elastic Wave Exploration Seismology Award for Best Doctoral Thesis We wish to congratulate Jonathan Downton, a recent graduate student with CEWES, whose thesis was awarded the honor of Best Doctoral Thesis for the Department of Geology and Geophysics at the University of Calgary for the year 005. The thesis is entitled "Seismic parameter estimation from AVO inversion". CN Graduate Student Awards We wish to congratulate four of our graduate students who have received awards over the past year. Julie Aitken, an M.Sc. student with Dr. obert Stewart, has received the Alberta Graduate Scholarship and the John O. Galloway Memorial Scholarship. Fuju Chen, an M.Sc. student with Dr. Julie Aitken Julie Aitken Xiang Du Fuju Chen Albert Zhang Software Donation A new CEWES sponsor, Geophysical Exploration & Development Corporation (GEDCO), has donated $7,000,000 worth of software to be used by CEWES and the Department of Geology and Geophysics at the University of Calgary. The donated software, VISTA, is designed for PC-based processing of seismic and VSP data. VISTA will be utilized by students both in the Don Lawton, has received the CSEG Scholarship and the Alberta Graduate Scholarship. Xiang Du, a Ph.D. student with Dr. John Bancroft, received the CSEG and SEG Scholarships. Duojun (Albert) Zhang, an M.Sc. student with Dr. Larry Lines, was awarded the Alberta Graduate Scholarship. These awards represent a high level of achievement and we commend these individuals for the quality of their work. CN classroom and in their research projects. We thank GEDCO for this generous donation. CN CEWES at the CSEG CEWES members are looking forward to participating in the upcoming annual convention of the CSEG (Canadian Society of Exploration Geophysicists) from May in Calgary, Canada. Eighteen CEWES presentations will be given by various individuals (see listing next page). We will also be at Booth 30, near the Internet Cafe; come visit us there. In This Issue... CEWES Presentations at the CSEG Technical Article: Prestack Depth Migration with the Gabor Transform eminder of Meeting Dates New student introduction Two New Sponsors CEWES wishes to announce the support of two new sponsors. Oil Search Limited is an oil and gas exploration and development company. They have extensive holdings in Papua New Guinea, where they have operated since 199. They also have interests in Yemen, Egypt and Libya. Kuwait Oil Company holds as assets the complete petroleum holdings of the country of Kuwait. Its operations began in 1934, and its first discovery well is still producing today. We are pleased to welcome these two companies as sponsors and look forward to working together with them and their members. CN

2 CEWES NEWS Volume 17, No. 4-5 Apr-May 006 CEWES Presentations at the CSEG CEWES members will present the following eighteen papers at this year s convention. Monday Time Lapse Seismic Palomino oom E :15 - :45 Violet Grove CO Injection Project: Monitoring with Coueslan, Lawton Timelapse VSP Surveys Migration Techniques II Palomino oom H :15 - :45 Two Prestack Anisotropic Depth Migration Methods for Tilted Du, Bancroft, Lawton, Lines TI Media :45-3:15 Computing Gridded Traveltimes from the andom Locations Bancroft, Du of Three Known Points 3:15-3:45 Enhancing the FOCI Algorithm by Using a Weighted Least- Al-Saleh, Margrave Squares Approach 3:45-4:15 Prestack Depth Migration with the Gabor Transform Ma, Margrave Tuesday Geophysical Papers I Palomino oom H 10:00-10:30 Intrinsic and Apparent Seismic Attenuation in VSP Data Haase, Stewart 10:30-11:00 Seismic Attenuation (Q) Estimation from VSP Data Xu, Stewart AVO Methods Hall D, oom 1 11:00-11:30 A Simple Way to Improve AVO Approximations Ursenbach Multi-Component Hall D, oom 10:00-10:30 Interpretation of Baseline Multicomponent Seismic Data at Chen, Lawton the Violet Grove CO Injection Site, Alberta 10:30-11:00 Two Issues About the Application of VP/VS: Quality Zhang, Lines Improvement and Error Analysis Seismic Data Processing I Archie Boyce Theatre 1:15-1:45 Statics or Statistics? - The Near-Surface evisited Henley Wednesday Geophysical Papers III Palomino oom H 8:30-9:00 Enhancements in the Processing of GP Data at Maax Na, Aitken, Stewart, Bancroft Belize, Central America 11:00-11:30 Color and Polarity of Seismic Terrain Displays Lynch Seismic Data Processing II Archie Boyce Theatre 8:30-9:00 eflectivity Color Correction in Gabor Deconvolution Montaña, Margrave Mon. - Tues. Posters Exhibit Hall Geophysical Papers I Well-Seismic Bandwidth and Time-Lapse Seismic Characterization: Physical Considerations Liu, Lawton, Margrave Designing Wavefield Extrapolators Using a Weighted Least- Squares with a Transition Band Approach Al-Saleh, Bancroft, Margrave AVO Methods Spherical-Wave AVO Modelling in VTI Media Haase, Ursenbach Derivation of Generalized eflections From Point Sources in Ursenbach, Haase VTI Media

3 Prestack Depth Migration with the Gabor Transform Yongwang Ma and Gary F. Margrave CEWES NEWS Volume 17, No. 4-5 Apr-May 006 Introduction The Gabor depth imaging algorithm approximates generalized phase-shift-plus-interpolation (GPSPI) wavefield extrapolation using a Gabor, or windowed Fourier, transform to localize the wavefield. The key to an efficient algorithm is to develop an adaptive windowing scheme that only localizes the wavefield as required by the lateral velocity variation. If there is no lateral velocity variation then no localization (windowing) is required. When velocity varies rapidly, then many relatively narrow windows are required for accurate wavefield extrapolation. Programs have been coded with the adaptive windowing algorithm, which substantially reduces the computational burden in wavefield extrapolation when compared to the full GPSPI integral. We will illustrate the performance of this algorithm with images from prestack depth migration of the Marmousi dataset. Wavefield Extrapolation with the Gabor Transform The generalized phase shift plus interpolation (GPSPI) wavefield extrapolation is formulated as (Margrave and Ferguson, 1999; Margrave et al., 004) ψ P( xt, z+ z, ω) (1) = ψˆ ( k, z, ω) Wˆ ( k, x, z)exp( ik x ) dx where T T T T T T Wk ˆ (, x, z ) = exp( ik ( vx ( )) z ), T T z T ω ω k T, > k T v ( xt) v ( xt) kz(( v xt)) = ω ω i kt, < k, T v ( xt) v ( xt) () (3) To develop a Gabor approximation to equation (1), we introduce the approximation Wˆ( k, x, z) Ω ( x ) S ( x ) Wˆ ( k, z) T T j T j T j T Ω j( xt) = 1 (4) (5) where Z denotes integer collection, {Ω j } is a family of windows forming a partition of unity (POU), S j (x T ) is a split-step Fourier operator for phase correction in the Gabor imaging, 1 1 Sj( xt) = exp iω z vx ( T) v j Ŵ j (k T, z) is a wavefield extrapolator, ( ) Wˆ ( k, z ) = exp ik ( v ) z j T z j and the reference velocities, ν j, are given by v j = Ω ( x ) vx ( ) dx j T T T Ω ( x ) dx j T T, (6), (7). (8) Notice that in equation (7), k z is still calculated with equation (3), using the reference velocity corresponding to a specific window Ω j (see equation (8)) instead of ν (x T ). Using the approximate wavefield extrapolator (4) in (1) gives ψ ( x, z+ z, ω) = Ω ( x ) S ( x ) P T j T j T ψˆ ( k, z, ω) Wˆ ( k, z)exp( ik x ) dx T j T T T T (9) Equation (9) specifies our Gabor wavefield extrapolator. ψˆ is the Fourier transform with respect to x T and time t, x T denotes transverse coordinates (e.g., x T = x in D, x T = (x,y) in 3D), k T is the coordinate in the wavenumber domain corresponding to x T, denotes real domain for integrations, z is the step size of extrapolation in the z (vertical) direction, ω is the temporal frequency, and ν(x T ) denotes lateral velocities along a slab with thickness z. Equation (1) extrapolates wavefields at depth z down to depth z+ z in the frequency-wavenumber domain. Imaging the Acoustic Marmousi Velocity Structures with the Gabor Extrapolator The Marmousi synthetic data set has been widely used as a benchmark for testing depth imaging algorithms. The Marmousi velocity profile used in our depth imaging is shown in Figure (a). In the Marmousi synthetic data set, we have 40 shot records, each of which has 96 traces, with time extending to about.9 seconds. For each shot record, there are 41 extrapolation steps with step cont d on next page

4 CEWES NEWS Volume 17, No. 4-5 Apr-May 006 size z = 1.5 meters. We give here one of our best imaging results for the Marmousi model (see Figure 1). To see how the adaptive windowing algorithm works in the Marmousi velocity model, in Figure (b) we show windows versus the depth and the lateral coordinates' corresponding to the dimensions of the Marmousi velocity model used in the Gabor imaging. The corresponding Gabor depth imaging result is shown in Figure 1. This work is presented in greater detail in an extended abstract at It will also be presented at the 006 CSPG/CSEG/ CWLS National Convention on May 15th. CN Lateral Coordinate FIG. 1. Gabor imaging of Marmousi velocity model (a) Lateral Coordinate (b) Lateral Coordinate FIG.. Windowing Marmousi Velocity Model with the Adaptive Windowing Algorithm. In (a), the units of the scale on the right are in m/s; in (b), the units of the scale on the right are in number of windows. Note that the transverse coordinates in (b) are not the true coordinates. The figure in (b) consists of 40 columns of windows versus depth. These columns are created during the shot migrations. Each of these 40 columns windows versus depth corresponding to a velocity piece adapted from the whole Marmousi velocity model used for a single shot migration. We put the true transverse coordinates into the figure to make it roughly comparable with the transverse coordinates in the velocity model (a) to see how the windows are distributed. eminder of Upcoming Meetings In the previous issue of CEWES News we announced two important events to be held this year. We mention these dates again for the benefit of readers who may have missed that issue. On August 7-11, 006, CEWES will be cohosting a Seismic Imaging Summer School. This will be followed on August 14-18, 006 by a Geophysical Inversion Workshop. Further information is available at On Nov. 9 - Dec. 1, 006, we will hold our 18th Annual Sponsors Meeting. All interested members of sponsoring companies are invited to attend this event. CN

5 CEWES NEWS Volume 17, No. 4-5 Apr-May 006 New Graduate Student Jeffrey Tan, a native Calgarian, obtained a B.Sc. in Electrical Engineering (with Distinction) in 006 from the University of Calgary. For 16 months (from May 004 to September 005), Jeff was on an engineering internship in Burlington, Ontario, where he worked at Gennum Corporation and was involved in integrated circuit design and characterization. He is currently pursuing his M.Sc. degree in Geophysics at the University of Calgary under the supervision of Dr. obert Stewart. His research interests include seismic data processing, interpretation, and analysis as it applies to the energy industry. Jeff aims to complete his M.Sc. by the end of August 007. Immediately following that, he plans on working as a Geophysicist in the energy industry. Jeff s hobbies include long distance running and playing the piano. CN Making Contact... Contact Note: eaders wishing to contact staff and students should add the to the usernames listed below. Directors: Dr. obert Stewart: stewart Dr. Gary Margrave: margrave Dr. Don Lawton: lawton Dr. Larry Lines: lrlines Associated Faculty Members: Dr. John Bancroft: bancroft Dr. Larry Bentley: lbentley Administrative Manager: Louise Forgues: forgues esearch Staff: Henry Bland: bland Dr. Zuolin Chen: zlchen Dr. Pat Daley: pdaley Eric Gallant: egallant Dr. Arnim Haase: haaseab Kevin Hall: kwhall Dave Henley: dhenley Han-Xing Lu: hxlu Dr. olf Maier: maier Jeff Thurston: jthursto Dr. C. Ursenbach: cursenba Dr. Joe Wong: wongjoe Visiting Scholars: Dr. Hanming Gu: hgu Graduate Students: Julie Aitken: jaitken Saleh Al-Saleh: salsaleh ichard Bale: rabale Zhihong (Nancy) Cao: zcao Fuju Chen: fjchen Marcia Coueslan: mlcouesl Xiang Du: xdu Pavan Elapavuluri: pkelapav Hong (Jason) Feng: hfeng Chad Hogan: cmhogan Michael Hons: msjhons Steve Lynch: lynchs Yongwang Ma: yongma Keith MacQuarrie: kimacqua Faranak Mahmoudian: fmahmoud Peter Manning: pmmannin Jason McCrank: mjmccran John Millar: jdmillar Carlos Montaña: rcamonta Hesham Moubarak: hmoubara Jeffrey Tan: jftan oxana Varga: rmvarga Tingge Wang: tinwang Chunyan (Mary) Xiao: cmxiao Chuandong (ichard) Xu: cdxu Duojun (Albert) Zhang: dazhang Jianlin (John) Zhang: jlzhang Zimin Zhang: zzhan