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WesternGecoLevel 4, School of Petroleum Engineering, Adelaide University, Adelaide 5005.

Data Processing ReportFor

SANTOS

Survey: MUNRO L3D

Cooper Basin Australia

Processing:Pre-Stack Time Migration

WesternGeco contract number: cg85 June 2009 – October 2009

Report Author: David Rowe

WG contract: Processing report for Survey: Munro P 2

WG contract: Processing Report for Survey: Munro P 2

Contents

1 Introduction.................................................................................................................................................41.1 General Description................................................................................................................................41.2 Key Personnel........................................................................................................................................51.3 Acquisition Plots.....................................................................................................................................6

1.3.1 Fold of Coverage.............................................................................................................................62 Processing Parameters...............................................................................................................................7

2.1 Production Processing Flow Summary...................................................................................................72.2 Processing Parameters..........................................................................................................................9

2.2.1 Reformat/Nav merge.......................................................................................................................92.2.2 De-phase/Re-sample/De-spike.......................................................................................................92.2.3 Noise Attenuation............................................................................................................................92.2.4 Preliminary velocity analysis...........................................................................................................92.2.5 RNA and 3D FK..............................................................................................................................92.2.6 Deconvolution.................................................................................................................................92.2.7 SCAC..............................................................................................................................................92.2.8 SCAC velocity analysis...................................................................................................................92.2.9 Residual Statics............................................................................................................................102.2.10 Residual velocity analysis.............................................................................................................102.2.11 TRIM statics..................................................................................................................................102.2.12 Offset split.....................................................................................................................................102.2.13 Regularisation...............................................................................................................................102.2.14 Targeted Migration for velocity analysis........................................................................................112.2.15 Targeted velocity analysis.............................................................................................................112.2.16 Pre-stack time Migration................................................................................................................112.2.17 Inverse Moveout & 3D CMP Sort..................................................................................................112.2.18 Final velocity analysis....................................................................................................................112.2.19 Final mute.....................................................................................................................................112.2.20 Radon Gathers..............................................................................................................................112.2.21 Near & Far Stack Generation........................................................................................................122.2.22 Full Fold Polygon selection...........................................................................................................122.2.23 SEGY Gather Archive...................................................................................................................122.2.24 SEGY Stack Archive.....................................................................................................................12

2.3 QC CMP Gathers.................................................................................................................................123 Processing Description............................................................................................................................13

3.1 Format Conversion...............................................................................................................................133.2 Geometry Update.................................................................................................................................133.3 Grid Define...........................................................................................................................................15

3.3.1 Munro Processing Grid..................................................................................................................153.4 Amplitude Gain Recovery.....................................................................................................................163.5 Minimum Phase Conversion.................................................................................................................163.6 Noise Attenuation.................................................................................................................................173.7 Preliminary Velocity Analysis................................................................................................................173.8 3D-RNA and 3D-FK in the Cross Spread Domain................................................................................173.9 Surface Consistent Deconvolution.......................................................................................................183.10 Surface Consistent Amplitude Compensation...................................................................................183.11 Pre Stack Gain..................................................................................................................................183.12 Common Midpoint Sort.....................................................................................................................183.13 SCAC velocity Analysis.....................................................................................................................183.14 Mute..................................................................................................................................................193.15 Residual Statics................................................................................................................................193.16 Residual Velocity Analysis................................................................................................................193.17 Trim Statics Analysis........................................................................................................................203.18 COMMON OFFSET GATHER.............................................................Error! Bookmark not defined.3.19 AMPLITUDE RECOVERY...................................................................Error! Bookmark not defined.3.20 TIME MIGRATED VELOCITY ANALYSIS...........................................Error! Bookmark not defined.3.21 DMO................................................................................................................................................. 213.22 HOLEFILL.........................................................................................................................................22

3.23 KXKY FILTER...................................................................................................................................22



3.24 INVERSE DMO.................................................................................................................................223.25 PRE STACK TIME MIGRATION.........................................................Error! Bookmark not defined.3.26 PRE STACK TIME MIGRATED VELOCITY ANALYSIS......................Error! Bookmark not defined.3.27 NMO................................................................................................................................................. 233.28 FINAL MUTE.......................................................................................Error! Bookmark not defined.3.29 RADON DEMULTIPLE.....................................................................................................................233.30 POST MIGRATION TESTING..........................................................................................................233.31 PRE STACK TIME MIGRATED STACK...........................................................................................233.32 POST STACK PROCESSING..........................................................................................................243.33 NEAR & FAR OFFSET STACKS......................................................................................................24

4 Final Stack QC Images..............................................................................................................................255 DELIVERABLES.........................................................................................................................................276 SEGY HEADER..........................................................................................................................................28

FiguresFigure 1 Gantt chart tracking progress of processing...........................................................................................4Figure 2 Progress Tracking Chart of Processing..................................................................................................5Figure 3 Munro and Gigee Source & Receiver Plot..............................................................................................6Figure 4 PSTM Fold of Coverage.........................................................................................................................6Figure 5 Munro Elevation....................................................................................................................................13Figure 6 Gidgee Elevation..................................................................................................................................14Figure 7 Munro Field Static Correction...............................................................................................................14Figure 8 Gidgee Field Static Correction..............................................................................................................15Figure 9 Combined Processing Grid...................................................................................................................16Figure 10 Minimum Phase Operator Sweep Before and After............................................................................17Figure 11 Munro Residual Statics.......................................................................................................................19Figure 12 Preliminary Inline Stack of 1835 and 2196 prior to 3D FKxKy noise attenuation.................................25Figure 13 Residual Inline Stacks of 1835 and 2196 prior to TRIM statics and Regularization............................25Figure 14 Regularized Inline Stacks of 1836 and 2196......................................................................................26Figure 15 Raw Migrated Inline Stacks of 1836 and 2196...................................................................................26



1 Introduction

1.1 General Description

This report details the processing of the combined MUNRO 3D seismic survey.

The report specifically details the processing of the MUNRO 3D seismic survey it also includes the re- processing of the GIDGEE 3D survey from field data. The surveys were seamlessly merged into a single volume.

Munro was acquired between April 27th 2009 and May 2nd 2009. It is 32 km2. It consisted of 22 receiver lines, 1000-1176 incrementing by 8 each 280m apart. There were 21 source lines, 5000-5168 incrementing by 8 and 280m apart.

Gidgee was acquired in 2006. Bin sizes were rectangular, 35 x70 metres.

Data processing commenced in June 2009 and was complete in September 2009. The project was coordinated and processed in WesternGeco’s Adelaide Data Processing centre. All processing was performed using WesternGeco’s Omega processing software.

The main objective of the processing was to provide a more detailed structural and stratigraphical definition of the Munro Field to provide optimisation of well locations for field appraisal and development.

Throughout the processing, WesternGeco maintained a close relationship with Santos representatives Philip Gatley and Kristina Dukic. This enabled rapid decision making and fine tuning of processing parameters and methods.

Figure 1 Gantt chart tracking progress of processing



Figure 2 Progress Tracking Chart of Processing

1.2 Key Personnel

Key individuals involved in the project were:

For Santos:Philip Gatley Kristina Dukic

For WesternGeco:Alison Keighley Data Processing ManagerKingSeong Tan Staff GeophysicistPhil McBride Data Processing SupervisorDavid Rowe Project Leader



1.3 Acquisition Plots

Figure 3 Munro and Gigee Source & Receiver Plot

1.3.1 Fold of Coverage

Figure 4 PSTM Fold of Coverage



2 Processing Parameters

2.1 Production Processing Flow Summary





2.2 Processing Parameters

2.2.1 Reformat/Nav merge:Reformat from SEG-D to Omega format Apply field shot edits, edit noisy traces Create and merge navigation to data

2.2.2 De-phase/Re-sample/De-spike:Convert from zero to minimum phase4ms resample (anti-alias high cut filter 0.84 Nyquist (105Hz), 60dB/oct) 4 dB/s Exponential GainSpherical Divergence compensation

2.2.3 Noise Attenuation:Edit spiky tracesMild Attenuation of anomalous amplitudes NMO corrected

250msec windows5Hz frequency bands41 trace width spatial median filter Threshold factor of 50 used

2.2.4 Preliminary velocity analysis:Moveout with constant velocity function Outside Mute15 Fan functions with 2% separation1.75x1.75km grid (select every 100 inline and crossline)

2.2.5 RNA and 3D FK:Sort traces to cross spread gather domain 3D RNA (FX deconvolution)

Inline & Crossline operator width 7 Inline and Crossline window width 28

3D FKDip of +/- 10 degrees was applied in the Inline and Crossline direction.Adjusted to +/- 10 degrees in the Inline, +/- 20 degrees in the Crossline direction for Gidgee.

2.2.6 Deconvolution:Surface Consistent Deconvolution

Temporal (Half) length of autocorrelation 500msec Analysis Window 200-16000msecFrequency Ranges for analysis 5-90Hz Active Operator length 160msecMoveout velocity for window start 1800m/sec

2.2.7 SCAC:Surface Consistent Amplitude Compensation

Hyperbolic window design 200-2700msec

2.2.8 SCAC velocity analysis:Velocity analysis on Munro and Gidgee surveys separately



Moveout with preliminary velocity function Outside Mute applied to Semblance and MVFS 15 Fan functions with 2% separation875x875m grid (select every 50 inline and crossline)

2.2.9 Residual StaticsMISER Residual statics

Window design 700-1400msec Shift Limit 32msec

2.2.10 Residual velocity analysis:Combined analysis for both surveys Moveout with SCAC velocity function applied Apply Miser staticsOutside Mute applied to Semblance and MVFS 15 Fan functions with 2% separation875x875m grid (select every 50 inline and crossline)

2.2.11 TRIM statics:Applied to surveys separately, enabling retention of orthogonal bins on Gidgee. Non-surface consistent static

Window 700-1400. Shift limit 8msecTraces with greater shifts retained

2.2.12 Offset splitGathers split into 28 common offset groups

Offset distribution can be found in section 3.16Sorted to CMP and offset

2.2.13 RegularisationCommon offsets for surveys merged on input DMO was applied to common offsets

Primary and Secondary Direction Filter Length:3Primary and Secondary Direction maximum wave number: 75% Nyquist

Hole FillInline Trace interpolate post stack

Max interpolation: 3 traces

Crossline Trace interpolate post stack Max interpolation: 8 traces

kxkyWindow design

200x200 traces 80x80 overlap 500msec length

K-notch filterNotch filter width 0.2 Notch filter taper 0.1

Inverse DMOSame parameters as DMO but in reverse order



2.2.14 Targeted Migration for velocity analysisKirchhoff Time Migration ran on every 25th Inline

Migration split over 28 offsets. See table in section 3.16.Input on 17.5m x 17.5m grid Migration Aperture = 3km:Time variant dip.

2.2.15 Targeted velocity analysisMoveout with Residual velocity function appliedRadon demultiple applied to gathers with moveout range +/- 2000m Outside Mute applied to Semblance and MVFS15 Fan functions with 1% separation875x875m grid (select every 50 inline and crossline)

.

2.2.16 Pre-stack time MigrationKirchhoff Time Migration

Migration split over 28 offsets. See table in section 3.16.Input on 17.5m x 17.5m grid Migration Aperture = 3km:Time variant dip.

2.2.17 Inverse Moveout & 3D CMP SortInput 28 Migrated offsets Full 3D CMP sortBack off migration velocities

2.2.18 Final velocity analysisMoveout with Targeted velocity function appliedRadon demultiple applied to gathers with moveout range +/- 2000m Outside Mute applied to Semblance and MVFS15 Fan functions with 1% separation437.5x437.5m grid (select every 25 inline and crossline)

2.2.19 Dense Velocity AnalysisDVA applied on a 3x3 CMP gather grid. Analysis on gathers with greater than 15 FoldTRIM Mean Filter with 40% constraint applied to Raw Semblance pickDVA blended with interpolated velocities over first ???? msecs.

2.2.20 Final muteFinal offset mute applied to the NMO corrected gathers prior to stack for the Raw PSTM

2.2.21 Radon GathersRadon Demultiple

Model moveout range -2000ms to 2000ms Reference offset distance 3100mVelocity mute: 96% 500m velocity field



2.2.22 Near & Far Stack GenerationNear and Far stack were produced for final deliverable, using mutes supplied. See section 3.31.

2.2.23 Full Fold Polygon selectionUse Line end coordinates as polygon to remove migration artefacts.

2.2.24 SEGY Gather ArchiveSurface Consistent amplitude corrected Decon Gathers

4msec sample rate4 second record length Residual statics appliedTRIM statics written to headers Time of first sample = 0 msec

Pre Stack Time Migration Gathers 4msec sample rate4 second record lengthTime of first sample = 0 msec

Radon Gathers4msec sample rate4 second record lengthTime of first sample = 0 msec

2.2.25 SEGY Stack ArchiveFull Stack

NMOSupplied mute

Near and Far stack as specified above.

2.3 QC CMP Gathers

Throughout the processing sequence the following were consistently used as QC gathers and QC stacks:

Munro: Inline 2196 Crosslines 10151 - 10190Gidgee: Inline 1836 Crosslines 10253 - 10292



3 Processing Description

3.1 Format Conversion

Field data was supplied by Santos and consisted of: SEG-D field data on a single LTO2 tape for Munro SEG-D field data on a single LTO2 tape for Gidgee

Input dataset was recorded to 4000msec and sampled at 2msec. The data was converted to Omega internal format and every 500th shot was output to SEG-Y for QC.

3.2 Geometry Update

Field geometry data was supplied in SPS format. It included positioning data, elevations and field static corrections for source and detectors. A geometry database was created and merged with the seismic data.

Figure 5 Munro Elevation



Figure 6 Gidgee Elevation

Figure 7 Munro Field Static Correction



Figure 8 Gidgee Field Static Correction

3.3 Grid Define

Processing grids were defined to allow sorting to the CMP domain.The primary ordinal number was defined to be two times the source line number and the secondary ordinal number was defined to be two times the detector line number.To allow the retention of orthogonal bins for 3DFK and TRIM calculations on Gidgee, the surveys were processed on individual grids up to AMO where they were combined on the Munro square bin grid.

3.3.1 Munro Processing Grid:

X COORD Y COORD PRIMARYORDINAL

SECONDARYORDINAL

508168.75 6840129.75 9950 1550508168.75 6849409.75 10486 1550523078.75 6840129.75 9950 2402523078.75 6849509.75 10486 2402

The cell size for this grid is 17.5 m x 17.5 m.

A display of the processing grid is shown below.



Figure 9 Combined Processing Grid

3.4 Amplitude Gain Recovery

Spherical Divergence Compensation & Exponential Gain 4 dB/sec was applied to both surveys.

3.5 Minimum Phase Conversion

An operator was derived from the filtered sweep trace (aux channel 2) and used to convert that data from zero to minimum phase. The autocorrelated sweep before and after the application of the operator is displayed below.



Figure 10 Minimum Phase Operator Sweep Before and After

3.6 Noise Attenuation

Records flagged as bad in the Observer's logs or as displayed in the QC plots were edited from the processing sequence.

A mild AAA (anomalous amplitude attenuation) was used to remove ground roll and spikes or excessive noise from any traces. this attenuates the noise by transforming the gathers into the frequency domain and applying a spatial median filter. Frequency bands that deviate from the median amplitude by a specified threshold are zeroed.

3.7 Preliminary Velocity Analysis

Velocity analysis was performed using WesternGeco’s Interactive Velocity Processing (INVA) package. For each velocity location, MVF data, semblances and gathers are displayed interactively allowing stacking velocities to be interpreted. NMO processed CMP gather data were input to velocity analysis. From this data Multi-velocity Function (MVF) stacks and velocity semblance displays were computed. For each velocity location the gathers, MVF data and semblances are displayed in separate windows on the workstation. Changes made to one window are automatically applied to all other windows. Velocities can be picked from either the MVF or semblance display. When velocities are interpreted at a location a velocity database is updated and the CMP gather is displayed with the NMO correction.

The preliminary velocity analysis was run every 1.75km. The velocities were QC’ed by representatives of Santos.

3.8 3D-RNA and 3D-FK in the Cross Spread Domain



The data was split into 23 detector lines. Each cross spread gather consisted of all traces that were recorded from all sources from one source line from each detector line.

3D-RNA (FX deconvolution) was applied to reduce random noise.

Using a Fourier transform, 3D-FK converts the gathers from a function of reflection time (t) and trace position (x) to that of a temporal frequency (f) and spatial frequency or wavenumber (k). The 3D f-k domain uses the inline and crossline spatial frequency components and is known as the f-kx-ky domain. Dip filtering in this domain uses a conical or pyramidal shape filter that is either pass or reject, creating an efficient way of eliminating unmawted noise.

Dips of 8, 12, 16 and 20 ms/tr were evaluated. Test displays were produced on gathers and on stacked data.

The dip selected was 10.0 ms/tr

3.9 Surface Consistent Deconvolution

Surface Consistent Deconvolution aims to compress the basic source and receiver wavelet. This method provides independent control of the source, receiver, cmp, and channel components of the system.

All tests were run using a design window at the near trace of 200 – 1600 msec. As the survey was quite small, stack panels were produced over the entire Munro are with

1) No deconvolution2) 80 ms spike3) 120 ms spike4) 160 ms spike5) 200 ms spike

It was decided to use surface consistent 160 ms Spiking Deconvolution.

3.10 Surface Consistent Amplitude Compensation

Seismic traces are decomposed into the effects of source, detector, offset and the CMP term: the earth’s reflectivity. The Surface-Consistent Amplitude Correction (SCAC) attempts to compensate for shot, detector or offset amplitude variations within a given seismic data set. After SCAC processing, the amplitudes for a given shot, detector or offset should be the same as for any other shot, detector or offset respectively.

The window used for SCAC was 200-2700msec.

3.11 Pre Stack Gain

For the residual & trim static computation processing, 500ms gates with 10% overlap were applied.

3.12 Common Midpoint Sort

The data was sorted to common midpoint order.

3.13 SCAC velocity Analysis

As above, SCAC velocity interpretation was conducted using WesternGeco’s InVA software. Velocities were run at 875m intervals.15 Fan functions with 2% separation were analysed.



3.14 Mute

Pre Stack Mute appliedOffset (m) Time (ms)

350 4500 4501200 9501700 14002300 1800

The Mute was supplied by Santos and eliminated far offset stretch. A brute stack was produced at this stage.

3.15 Residual Statics

The determination of residual statics consists of two parts, the statics deviation picker and the statics computation. The picker derives reflection times and quality factors. The statics are obtained by decomposing the reflection pick times into surface consistent source and receiver statics using the Gauss-Seidel iterative algorithm. The window used for Residual Statics Analysis was 700 – 1400msecs.

Figure 11 Munro Residual Statics

3.16 Residual Velocity Analysis

Gathers with Residual statics applied were combined from both surveys. Velocity interpretation was conducted using WesternGeco’s InVA software.Velocities were run at 875m intervals.15 Fan functions with 2% separation were analysed.



3.17 Trim Statics Analysis

Trim Statics analysis was run over a 700 - 1400 ms window with a maximum shift of 8 ms allowed. This process was run separately for Munro and Gidgee with the original survey geometry.The trim statics were applied and the volume was stacked for QC.

3.18 Common Offset Gather

Surface consistent deconvolved data with was sorted into common offset gathers using a statistical equal trace distribution method.Residual statics and the trim statics were applied.Gidgee utilized overlap offsets to increase the fold per bin.

Table showing Offset Groups with minimum and maximum offsets in metres for Munro.Offset Group Minimum Offset Maximum Offset Offset1 0 210 1052 210 350 2803 350 420 3854 420 490 4555 490 560 5256 560 630 5957 630 700 6658 700 770 7359 770 840 80510 840 910 87511 910 980 94512 980 1050 101513 1050 1120 108514 1120 1190 115515 1190 1260 122516 1260 1330 129517 1330 1400 136518 1400 1470 143519 1470 1540 150520 1540 1610 157521 1610 1680 164522 1680 1750 171523 1750 1820 178524 1820 1890 185525 1890 1960 192526 1960 2030 199527 2030 2170 210028 2170 3000 2310

Table showing Offset Groups with minimum and maximum offsets in metres for Gidgee.Offset Group Minimum Offset Maximum Offset Offset1 0 280 1052 140 420 2803 315 455 3854 385 525 4555 455 595 525



6 525 665 5957 595 735 6658 665 805 7359 735 875 80510 805 945 87511 875 1015 94512 945 1085 101513 1015 1155 108514 1085 1225 115515 1155 1295 122516 1225 1365 129517 1295 1435 136518 1365 1505 143519 1435 1575 150520 1505 1645 157521 1575 1715 164522 1645 1785 171523 1715 1855 178524 1785 1925 185525 1855 1995 192526 1925 2065 199527 1995 2240 210028 2000 3000 2310

3.19 Amplitude Recovery

The Spherical Divergence Compensation & Exponential Gain were removed prior to the PreStack Time Migration

3.20 Time Migrated Velocity Analysis

The surveys were merged and a targeted velocity line migration was run to output fully migrated gathers along selected velocity lines. Velocities were run at 875m intervals on these pre stack time migrated gathers. Velocity interpretation was done using WesternGeco’s InVA software. The velocity field was smoothed for use in the full Kirchhoff migration.15 Fan functions with 1% separation were analysed.

3.21 DMO

Pre-stack Kirchhoff time migration was to be performed to fully image the dataset. However, forward and reverse DMO was applied to the offset volumes prior to migration in order to regularise the fold and place each trace at its bin-centre position i.e. all output traces at single inline aperture. It was hoped that additional potential benefits of DMO, e.g. attenuation of residual dipping noise might also occur.

Dip Moveout (DMO) is a process that attempts to take traces recorded at a non-zero offset and make them appear as if they had been recorded with zero offset. It can therefore be thought of as a pre-stack partial migration. After DMO has been applied several goals are achieved:DMO was applied using the Kirchhoff integral method in the X-T domain. This method works by spreading energy from one trace to its neighbours along the DMO ellipse (the input having had NMO applied). The shape of the ellipse was computed from a constant-velocity algorithm; truncating and tapering the ellipse produced the DMO operator that was applied along the shot-receiver azimuth.



The limbs of the DMO operator have progressively steeper dips, which results in spatial aliasing occurring at progressively lower frequencies, as one moves out along the operator. To reduce the impact of aliasing the limbs of the operator were time and space variantly high-cut filtered to remove aliased energy from the operator.

At near offsets the DMO operator can quickly reach the stage where its width is comparable to or smaller than the mid-point spacing. Where this occurs accurate amplitude treatment of the data is compromised if the spatial sampling of the operator remains at or greater than the mid-point spacing. To correct for this the operator was super-sampled (spatially) at near offsets. This option, referred to as Hi-Fi DMO, ensures accurate treatment of amplitudes even at very short offsets.

DMO relies on constructive and destructive interference of the various operators in order to formulate the output image and can be heavily influenced by the acquisition geometry of the input data. Any deficiencies in this geometry can result in: Poor reflection amplitude and phase reconstruction.

Noise (residual energy) from irregularly sampled DMO operators within a gather.

A combination of Equalisation DMO (EQ DMO) and Spatially Unaliased DMO (FAT DMO) was used to mitigate these effects.EQ DMO works by analysing the geometry of every trace to determine the DMO contribution being made to each and every output location, and calculating the appropriate normalisation factor. The DMO contributions can be loosely segregated into different offset ranges, dip ranges and azimuth ranges in order to fine-tune this equalisation.

In FAT DMO two sets (inline and crossline) of a 2-D modified sinc function are used to interpolate DMO contributions to cell centre. In this way, the initial DMO correction, which was along the source-receiver trajectory, is now spread to cells surrounding the trajectory. This ensures that the requirement for effective implementation of DMO - that the operator is regularly sampled at all times in all cells - is better achieved.

3.22 Holefill

Each offset plane had missing traces interpolated using a post stack 2D trace interpolator in both the inline and crossline directions.

3.23 KXKY Filter

A post stack KXKY filter was applied to each offset plane to reduce the acquisition footprint.

3.24 Inverse DMO

The bin-centred regularised data underwent inverse DMO along the inline azimuth.

3.25 Pre Stack Time Migration

The Kirchhoff Time Migration Seismic Function Module (SFM) performs seismic time migration using the Kirchhoff summation method. The migrated image is constructed by summing weighted amplitudes along diffraction curves or curved surfaces for the 3D case. These diffraction curves are determined by two-way travel times from the surface to subsurface scatterers that are computed from the user-supplied velocity field. In prestack mode, migration is performed on common offset volumes for 3D data.Pre-stack migration is achieved by migrating the sorted common-offset panels into individual zero-offset panels. During migration the traces are effectively NMO-corrected; however, inverse NMO using the migration velocity is typically applied prior to output of the data. This allows a final velocity analyses and moveout to be performed on the data prior to stacking it.

The data was moved back to the smoothed surface from the mean sea level datum.



3.26 Pre-stack Time Migration Velocity Analysis

The migrated output data was sorted to cmp order and the smoothed migration velocity field was removed. Post migration velocities were run at 375m intervals.Velocity interpretation with 15 Fan functions with 1% separation were analysed using WesternGeco’s InVA software.

3.27 Dense Velocity Analysis (DVA)

DVA provides a method of resolving high resolution velocity fields needed for prestack imaging. It uses a guided automatic velocity picker using a semblance optimization approach to create a velocity cube.The pre-stack time migration velocity analysis was used to guide the automatic picking. This increased the density of picks from a 375 x 375m grid to 52.5 x 52.5m (one every 3 CMP’s).A surface constraint was applied which started picking at 300msec with a RMS velocity of 1720m/s. A 3D TRIM filter was applied to the raw picks which had a 40% cut off.

3.28 NMO

The velocity functions were applied to the data

3.29 Final Mute

Pre Stack Mute applied

Offset (m) Time (ms)385 0455 4501365 10001855 13002310 1500

The Final Mute was supplied by Santos and eliminated far offset stretch. This mute was applied to the Raw PSTM stack.

3.30 RADON DEMULTIPLE

A radon demultiple using a 96 pct velocity mute was tested and applied to produce gathers only. The radon demultiple was not applied to the final stack.

3.31 POST MIGRATION TESTING

Various post migration tests were run. Tests included:

TRIM calculated and applied to PSTM gathers TRIM calculated on Radon gathers and applied to PSTM gathers TRIM applied to stacks Spectral Whitening and MONK Whitening

3.32 PRE STACK TIME MIGRATED STACK

The data was stacked and subsequently shifted from the smoothed surface to the mean sea level datum.



3.33 POST STACK PROCESSING

Post stack processing was not applied by WesternGeco. It was done in house by Santos. Spectral Whitening: 8-10-75-80Hz 3 panelsFXY Decon: 9x9 filterScale: mild 4 window time variant scalar. 200-1000, 800-1300, 1000-2000, 1400-3000ms

3.34 NEAR & FAR OFFSET STACKS

Near Stack was produced with the following Mute:

Offset (m) Time (ms)385 0525 700735 900805 10001015 12001295 14001435 16001505 1700

Far Stack was produced with the following Mutes:

Inner Mute Outer MuteOffset (m) Time (ms) Offset (m) Time (ms)

105 400 385 0285 560 455 460595 840 1015 800735 1000 1435 1000945 1200 1785 12001225 1400 1995 13201435 1600 2310 14001505 1700



4 Final Stack QC Images

Figure 12 Preliminary Inline Stack of 1835 and 2196 prior to 3D FKxKy noise attenuation

Figure 13 Residual Inline Stacks of 1835 and 2196 prior to TRIM statics and Regularization



Figure 14 Regularized Inline Stacks of 1836 and 2196

Figure 15 Raw Migrated Inline Stacks of 1836 and 2196



DELIVERABLES

Intermediate stacks were output in SEGY format on DVD.

Decon cmp gathers were output in SEGY format to LTO tape. Velocities and statics not applied. Statics in headers.

Final PSTM gathers both with and without radon were output in SEGY format to LTO tapes. Statics and velocities applied.

The final stack archives were produced in SEGY.

RAW PSTM – 2 copies (LTO) 1 copy (DVD)RAW PSTM (NO RMS)– 2 copies (LTO) 1 copy (DVD)FINAL PSTM (SW) – 2 copies (LTO) 1 copy (DVD) FINAL PSTM (MONK) – 2 copies (LTO) 1 copy (DVD)NEAR STACK – 2 copies (LTO) 1 copy (DVD) FAR STACK – 2 copies (LTO) 1 copy (DVD)

The final DVA velocities in text and segy were produced on DVD



5 SEGY HEADER

The following is an example of the segy ebcdic header showing the byte locations of stored trace header information.

*** SEGY EBCDIC HEADER ***

C01C02

CLIENT : SANTOSAREA : MUNRO

C03 INLINE : 1600-2351C04 XLINE : 10000-10431C05 FINAL STACK (MONK)C 6 SAMPLE INTERVAL 4.00 SAMPLES/TRACE 1001 BITS/IN BYTES/SAMPLE

4C 7 RECORDING FORMAT FORMAT THIS REEL SEG-Y MEASUREMENT SYSTEM

METERSC08 SEGY BYTE LOCATIONSC09 XCORD CELL CENTRE 81-84 YCORD CEL CENTRE 85-89C10 SOURCE STATIC 99-100 DETECT STATIC 101-102C11 SORUCE RESID 185-188 DETECT RESID 189-192C12 INLINE ORDINAL 197-200 XLINE ORDINAL 201-204C13 SOURCE ELEV 225-228 DETECT ELEV 229-232C14C15

CMP DATCORGRID X

233-236Y PRIM ORD SEC ORD

C16 508168.75 6840129.75 9950 1550C17 508168.75 6849509.75 10486 1550C18 523078.75 6840129.75 9950 2402C19 523078.75 6849509.75 10486 2402C20C21 PROCESSING PARAMETERSC22 CONVERT FROM SEGD TO OMEGA FORMAT C23 APPLICATION OF GEOMETRY AND GRIDC24 CONVERT TO MINIMUM PHASE RESAMPLE TO 4MSC25 GRIDDED FB STATICS GAIN APPLICATION AND DESPIKE(AAA) C26 SORT TO XSPREAD GATHERS 3D RNAC27 3DFK - CUTS +/- 10MS PER TRACE C28 SORT TO CMPC29 SURFACE CONSISTENT DECON 160MS SPIKE WIN 200-1600 NEAR TR C30 SURFACE CONSISTENT AMP COMPENSATION VELOCITIES 1KM SPACING C31 RESIDUAL STATICS 700-1400 MS WINDOWC32 PRELIM STACK VELOCITIES 1KM SPACING C33 TRIM STATICS 700-1400MS WINDOWC34 SORT TO COMMON OFFSET TARGETED PSTM ON VELOCITY LINES C35 MIGRATION VELOCITIES 500M SPACING INVERSE GAINC36 DMO KXKY INVERSE DMO PSTM POST MIGRATION VELS 500M SPACING C39 DVA VELOCITIES 52.5 X 52.5 MC38 TRIM STATICS 700-1400MS WINDOWC39 500 RMS GAIN MUTE STACK MONK WHITENING 10-80 FILT C40 END EBCDIC

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