processing report

8/16/2019 Processing Report

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Processing Report

for the

2004 Browse Basin

Kingshead

SK04-2D Survey

Area:

WA-338-P

October 2004

Robertson ResearchAustralia Pty. Ltd.

69 Outram StreetWest Perth WA 6005

Tel: +61 (08) 9322 2490Fax: +61 (08) 9481 6721

E-mail: [email protected]

Integrated Services in

Petroleum Exploration and Production


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TABLE OF CONTENTS

1 INTRODUCTION.....................................................................................................................................................3

1.1 PERSONNEL......................................................................................................................................................31.2 LOCATION MAP...............................................................................................................................................4

2 PARAMETER TESTING........................................................................................................................................5

3 COMMENTS & CONCLUSION............................................................................................................................6

4 PROCESSING SEQUENCE....................................................................................................................................7

4.1 PSTM SEQUENCE (FILTERED)......................................................................................................................74.2 PSTM ANGLE STACKS SEQUENCE (SCALED)..........................................................................................84.3 PSTM SEQUENCE (RAW)...............................................................................................................................94.4 PSTM ANGLE STACKS SEQUENCE (RAW)..............................................................................................104.5 PSTM GATHERS.............................................................................................................................................11

5 PROCESSING DESCRIPTION............................................................................................................................12

5.1 TRANSCRIPTION...........................................................................................................................................125.2 GAIN RECOVERY..........................................................................................................................................125.3 LOW-CUT FILTER..........................................................................................................................................125.4 SWELL NOISE ATTENUATION...................................................................................................................125.5 FX INTERPOLATION.....................................................................................................................................135.6 MULTI CHANNEL FILTER (SHOT DOMAIN)............................................................................................135.7 TAU-P DECONVOLUTION............................................................................................................................135.8 TAU-P LINEAR NOISE REMOVAL..............................................................................................................135.9 INTERPOLATED TRACES DROPPED ........................................................................................................135.10 CDP GATHER................................................................................................................................................135.11 FIRST PASS VELOCITY ANALYSIS.........................................................................................................14

5.12 REVERSE GAIN RECOVERY.....................................................................................................................145.13 APPLY TRANSMISSION LOSS...................................................................................................................145.14 SPHERICAL DIVERGENCE (URSIN & GAIN).........................................................................................145.15 FK MULTIPLE ATTENUATION.................................................................................................................145.16 PRE-STACK TIME MIGRATION (FIRST PASS).......................................................................................155.17 SECOND PASS VELOCITY ANALYSIS....................................................................................................155.18 PRE-STACK TIME MIGRATION................................................................................................................155.19 THIRD PASS VELOCITY ANALYSIS........................................................................................................155.20 NMO CORRECTION ....................................................................................................................................155.21 RESIDUAL RADON......................................................................................................................................165.22 OUTER TRACE MUTE.................................................................................................................................165.23 INNER TRACE MUTE .................................................................................................................................165.24 COMMON DEPTH POINT STACK.............................................................................................................16

5.25 STATICS.........................................................................................................................................................175.26 ZERO PHASE CONVERSION......................................................................................................................175.27 TAU-P FILTER .............................................................................................................................................175.28 FILTER...........................................................................................................................................................175.29 ANGLE STACKS...........................................................................................................................................17

6 APPENDICES.........................................................................................................................................................18

6.1 LINE LISTING.................................................................................................................................................186.2 ACQUISITION PARAMETERS.....................................................................................................................196.3 DELIVERABLES.............................................................................................................................................206.4 SEGY TRACE HEADERS (STACK)..............................................................................................................21

WA-338-P 2004 Kingshead 2D Processing Report Page 2


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1 INTRODUCTION

The 2004 Kingshead 2D Processing consisted of 18 lines totaling 422.69km.Line SK04-05 (strike) was used as our primary test line, whilst SK04-18 (dip) was used for

confirmation of tests.Water bottom depths were consistent across all lines with values varying between 100ms and160ms.Testing was undertaken based on the previous Browse Basin processing done by Robertson in2003. Parameters and the processing sequence were then adjusted as appropriate.

1.1 PERSONNEL

Robertson Research AustraliaSimon Stewart Marine 2D Manager

Heidi Best Geophysicist

Santos LimitedStuart Brew Senior Staff Geophysicist



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1.2 LOCATION MAP



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2 PARAMETER TESTING

Testing was performed on Lines SK04-05 and SK04-18 to determine the optimal parameters.

Please refer to the table below for a list of the tests performed.

Description Format

Raw displays Shot

Gain recovery Shot

Low Cut Filter Shot

Swell Noise Attenuation Shot

FK filter Shot

Tau-P Linear Noise Removal Shot/Stack

Tau-P Deconvolution Shot/Stack

Predictive deconvolution (before stack) Gather/Stack

FK Demultiple Gather/Stack

Radon demultiple Gather/Stack

Scaling before PSTM Testing (SCAMP) Gather/Stack

Pre stack migration velocity field smoothing Velocity profile

Pre stack migration aperture Stack

Anisotropic NMO corrections (ETA) Gather/Stack

Stack mutes (outer and inner trace) Gather/Stack Residual Radon Gather/Stack

Incident angles at 5 degree intervals Gather

Predictive deconvolution after stack Stack

Relative amplitude Stack

Zero Phasing Stack

Q Compensation Stack

Post stack scaling Stack

Phase rotation Stack

Parameter tests were presented as paper displays, or ftp'd to Santos in SEGY format forevaluation on screen.



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3 COMMENTS & CONCLUSION

The 2004 Kingshead 2D Processing began in early September 2004 and was completed bylate October 2004. The processing flow was chosen based on previous processing of the 2003Browse Basin Testing by Robertson. Testing of the above mentioned lines allowed for these

previous processing parameters to vary where necessary.

Residual Radon was applied to all final deliverables.

The final data was statistically zero phase converted and rotated for a zero phase waterbottom.

All processing parameters have been detailed in Section 5 – Processing Description.



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5 PROCESSING DESCRIPTION

5.1 TRANSCRIPTION

Field data were converted to Robertson’s internal format for processing. RRA’s internalprocessing format is trace sequential, with samples in 32 bit IEEE floating point. Atintermediate processing stages the data is stored on disk in sixteen-bit integer with a gainranging scalar for each trace. When reading the format shot records, strategic header valuesrelated to acquisition were preserved (where available).

5.2 GAIN RECOVERY

A gain function was applied to the data set to compensate for inelastic attenuation and sphericaldivergence

A t2 gain function was applied where t = two way travel time in milliseconds.

5.3 LOW-CUT FILTER

A low-cut filter of 4/12 Hz/dB/Octave was applied to the shot records.

5.4 SWELL NOISE ATTENUATION

Swell noise attenuation is achieved by shaping the amplitude spectra of selected "swell noise

affected" traces.

Analysis and attenuation are performed in the FX domain, processing one source position at atime. For analysis, the amplitude spectra are normalised, considering only the higher frequencyrange which is less influenced by swell noise. After normalisation the swell noise traces arerecognised by their relatively high amplitude, low frequency component. The shallow portionof each shot record is muted before analysis, removing the high amplitude shallow reflectionsand direct arrivals.

The user nominates a frequency range for analysis, and for spectral scaling. Typically thisfrequency range is from 0 to 32 Hz. Scalars are calculated to shape the spectra of individualswell noise affected traces to the mean of the non swell noise affected traces. The scalars are

fully applied from 0 to one half the defined frequency range, after which the scalars are taperedto zero application at the maximum defined frequency. No modification is made to other traces.

The mechanism of swell noise recognition is not influenced by change in source energy, or bysystematic variation in trace amplitude levels. Shots not affected by swell noise will not presentany traces for swell noise attenuation.

The swell noise attenuation is monitored by recording the number of channels flagged as beingaffected by swell noise.



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5.5 FX INTERPOLATION

All data underwent F-X interpolation (shot domain) with a window length of 1000ms.Processing was performed by interpolating a single trace in the centre of two original traces.

5.6 MULTI CHANNEL FILTER (SHOT DOMAIN)A symmetrical “velocity” filter was designed in the F-K domain to preserve the primaryreflection signal and to discriminate against coherent dipping noise trains. The filter employs acosine-squared taper from k = 0 to the velocity intercept at each frequency. Filtering wasapplied in the shot domain only. The input data was conditioned with a 300ms AGC, and thescalars preserved for removal subsequent to the application of the F-K filter. A cut off velocityof +/- 2000 m/sec was used and NMO was applied before and removed after the filter.

5.7 TAU-P DECONVOLUTION

The data was transformed to the Tau-P domain using the linear transform. Transform limits of -2500 ms to 2500 ms at an increment of 10 ms (951 ptraces) were used.

Predicitive deconvolution was performed in Tau-P space to target water layer reverberation.The design window for the deconvolution consisted of a single window, 200ms operator and agap length of 36ms. Application of the deconvolution was to the whole trace length.

5.8 TAU-P LINEAR NOISE REMOVAL

While in Tau-P space linear noise may be removed by the application of scaling or mutingsections of the transformed data that represent the noise energy. Careful design can preserve thelong offset primary data from being attenuated. For these data the following mutes wereapplied.

Water Bottom Time: 100 ms Delt times (ms)-2500 0 to 3192-1500 0 to 3192-1000 600 to 3192500 600 to 31921200 0 to 31922500 0 to 3192

5.9 INTERPOLATED TRACES DROPPED

Traces interpolated as per section 5.5 were discarded.

5.10 CDP GATHER

Shot records were sorted into common depth point gathers with a nominal fold of 120.



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Time (ms) Velocity %

0 94

800 92

2500 92

4500 90

Application times are with respect to gathers without NMO corrections.A 300ms AGC was applied before the FK transform, and the scalars preserved for laterremoval.

5.16 PRE-STACK TIME MIGRATION (FIRST PASS)

Kirchhoff PreSTM was applied using a maximum half aperture of 400 traces (2500m).Apertures were muted with a 50% stretch mute to avoid operator aliasing. Smoothed 100%

first pass 2 km velocities were used in the migration. Migration was performed on 2:1 summedoffset planes.

5.17 SECOND PASS VELOCITY ANALYSIS

The second pass of velocities were picked at 1km intervals on first pass PSTM gathers usingRobertson’s “MGIVA” interactive velocity analysis program. Each velocity analysis compriseda semblance display, a CDP stacked panel repeated 14 times with a suite of velocity functions,and a central CDP gather. The suite of functions were generated using 0%, +/-4%, +/-8%, +/-13%, +/-19 %, +/-25% , +/-32 % and +40% increments from a central velocity function. Thefirst pass of velocities were used as the central function for this suite of velocity variant

functions.

5.18 PRE-STACK TIME MIGRATION

Kirchhoff PreSTM was applied using a maximum half aperture of 400 traces (2500m). Anti-aliasing protection was applied by pre-filtering the data within the migration scan dependingupon the local migration operator dip. Smoothed 100% second pass velocities at 1 km wereused in the migration. Migration was performed on all offset planes.

5.19 THIRD PASS VELOCITY ANALYSIS

The third pass of velocities were picked at 0.5km intervals on second pass PSTM gathers usingRobertson’s “MGIVA” interactive velocity analysis program. Each velocity analysis compriseda semblance display, a CDP stacked panel repeated 14 times with a suite of velocity functions,and a central CDP gather. The suite of functions were generated using 0%, +/-4 %, +/-8%, +/-13%, +/-19 %, +/-25% , +/-32 % and +/40% increments from a central velocity function. Thesecond pass of velocities were used as the central function for this suite of velocity variantfunctions.

5.20 NMO CORRECTION

Fourth order NMO corrections were applied using the final picked 0.5km PSTM velocityfunctions.



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5.21 RESIDUAL RADON

Residual high resolution radon demultiple was applied to the final NMO corrected Kirchhoff PreSTM data.Radon demultiple, using 100% final velocities, was applied using 701p values betweenmaximum offset delta t values of –1000ms and 2500ms.

The Radon demultiple application times were:

WB Time (ms) Time (ms) / Moveout (ms) Pairs1 0/250, 1000/100, 2000/50, 6144/50

1000 0/150, 2000/100, 3000/50, 6144,50Reference Offset = 3053m

5.22 OUTER TRACE MUTE

A post NMO outer trace mute was applied to remove any coherent noise on the outer traces and

to reduce contamination from the effect of NMO stretch on the far offsets. Muting parameterswere spatially varied according to seafloor two way time.

WB Time = 100ms

Offset (m) Time (ms)

120 0

176 206

469 450

815 800

1455 1500

3059 2800

5.23 INNER TRACE MUTE

A post NMO inner trace mute was applied to help remove remnant multiple energy stillapparent on the inner traces following the demultiple.

Water Bottom Time: 100 msOffset (m) Application times (ms)

60 500 – tmax

300 1100 – tmax370 1500 – tmax

5.24 COMMON DEPTH POINT STACK

The traces within each CDP bin were summed using a 1/root(N) stack compensation. The anglestacks were summed using 1/N stack compensation.



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5.25 STATICS

A static compensation for gun and cable depths was applied. The static value applied wascalculated using average gun and cable depths supplied in the observers reports (7ms).

5.26 ZERO PHASE CONVERSIONThe data was converted from minimum phase data to zero phase, using the Weiner-Levinsondouble inversion method to derive an operator based on the amplitude spectrum. A constantphase shift of -90 was then applied.

5.27 TAU-P FILTER

A time-varient dip filter with AGC wrap was applied to all stack data.

5.28 FILTERUnwanted noise that lay outside the frequency range of the desired reflection data wasattendated by the application of a series of zero phase time variant filters. These filtersemployed cosine squared tapers between the limiting frequency pairs.

Application time (ms) Frequency limits (Hz)

1200 6 / 10 – 90 \ 100

2000 4 / 8 – 70 \ 80

3000 4 / 6 – 60 \ 70

5.29 ANGLE STACKS

Using the full inner trace mute and 120% of the outer trace mutes, the remaining 'live' data wassplit 50% / 50% to produce near and far angle stacks on both the raw and the filtered/scaledPSTM data.



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6 APPENDICES

6.1 LINE LISTING

Test lines have been highlighted in red.


LINE Total KMS

SK04-01 1001 3013 1 4264 12.5 25.16

SK04-02 1001 2334 1 2906 12.5 16.68

SK04-03 1001 3829 1 5896 12.5 35.36

SK04-04 1001 2350 1 2938 12.5 16.88

SK04-05 1001 4186 1 6610 12.5 39.83

SK04-06 1001 2360 1 2958 12.5 17

SK04-07 1001 4351 1 6940 12.5 41.89

SK04-08 1001 2335 1 2908 12.5 16.69

SK04-09 1001 5891 1 10020 12.5 61.14

SK04-10 1001 2339 1 2916 12.5 16.74

SK04-11 1001 2944 1 4126 12.5 24.3

SK04-12 1001 2250 1 2738 12.5 15.63

SK04-14 1001 2258 1 2754 12.5 15.73

SK04-16 1001 2260 1 2758 12.5 15.75

SK04-18 1001 2284 1 2806 12.5 16.05

SK04-20 1001 2262 1 2762 12.5 15.78

SK04-22 1001 2272 1 2782 12.5 15.9

SK04-24 1001 2297 1 2832 12.5 16.21422.69

First Proc

SP

Last Proc

SP

First Proc

CDP

Last Proc

CDP

SP Interval

(m)


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6.2 ACQUISITION PARAMETERS

DESCRIPTION DETAILS Data recorded by: Veritas DGC Australia

Date recorded: 2004Vessel: M/V Pacific Sword

General:-Field CMP Interval 6.25 m

Nominal Fold 120

Seismic source:-Type Bolt 1500LL & 1900LL-XT Airguns

Volume 1760 cu.in.Pressure: 1950 psi Depth: 5m +/- 1.0 m

Shot interval: 12.5 mGun Delay 0 ms

Recording system:-

Format: SYNTRAK 960-24 MSRS Record length: 3000 msSample interval: 2 ms

Number of Channels 240 Near Channel 240

Recording Delay 0 msFilters 3 Hz, 6 dB/octave

206 Hz ,276 dB/octave

Receivers:-Centre near group to centre far group: 2987.5 m

Streamer depth: 6m +/- 1.5 m Number of groups: 240

Group interval: 12.5 mCentre source to center near group: 72 m



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6.3 DELIVERABLES

Item Format Media Tape No.

Final Stacking Velocities (PSTM)0.5km Intervals & CMP Coordinates

Western/ASCII CD 357FV001CD

PSTM corrected gathers SEGY DLT 357GA002L

PSTM corrected gathers SEGY DLT 357GA003L

Final Filtered Migrations (Original)Zero PhasedFull, Near and Far Datasets

SEGY DVD 357FM004DVD

Final Filtered Migrations (Copy 1)Zero PhasedFull, Near and Far Datasets


Final Filtered Migrations (Copy 2)Zero PhasedFull Datasets Only


Raw Migrations (Original)Full, Near and Far Datasets

SEGY DVD 357RM007DVD

Raw Migrations (Copy 1)Full Near and Far Datasets

SEGY DVD 357RM008DVD

Final Processing Report(Original)

PDF CD 357FR009CD

Final Procesing Report(Copy 1)

PDF CD 357FR010CD

Final Processing Report(Copy 2)

PDF CD 357FR011CD

Final Processing Report Paper Copy



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6.4 SEGY TRACE HEADERS (STACK)

Type Offset Description

I32 0 Trace number within line.I32 4 Trace number within reel.I32 8 Sequential record number.I32 8 Original field record number.I32 12 Trace number.I32 16 Shot point number.I32 20 CDP number.I32 24 Trace no. within the CDP.I16 28 Trace identification code.I16 30 No. of summed traces.I16 32 Total number of traces in CDP.I16 34 Data use 1=production, 2=test.I32 36 Trace offset (integer).

I32 40 Elevation at receiver.I32 44 Elevation at source.I32 60 Water depth at source.I32 64 Water depth at receiver.I16 68 Scaler to be applied to elevationsI16 70 Scaler to be applied to coordinatesI32 72 Source easting.I32 76 Source northing.I32 80 Receiver easting.I32 84 Receiver northing.I16 88 Coordinate units (m/arc)I16 98 Source static correction.I16 100 Receiver static correction.

I16 102 Total static applied.I16 108 Delay recording time (ms).I16 110 Mute time start.I16 112 Mute time end.I16 114 No. of samples.I16 116 Samp interval in microseconds.I16 156 Year of recordingI16 158 Julian day number (1-366)I16 160 Hour of day (24 hour clock)I16 162 Minute of hourI16 164 Second of minuteI16 166 Time base code 1.local,2.gmt,3.?I16 180 Seqn record no. (pre-stack only)

I32 180 3D Line number.I32 184 CDP no. within 3D line.I32 188 2D shotpoint number (Maersk)I32 192 Easting of CDP.I32 196 Northing of CDP.I16 200 Scaler to be applied to SPNO.

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