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Southern Amadeus PSDM TRIAL Santos QNT Pty Ltd ABN 33 083 077 196

PSDM 2D Seismic Processing Report

Carried out by: SANTOS LTD

For: SANTOS LTD

Area: AMADEUS BASIN, NORTHERN TERRITORY

Survey: 2013 AMADEUS 2D

Method: 2D Land Processing


Table of Contents

1. INTRODUCTION .......................................................................................................................... 4

1.1 SCOPE OF REPORT ..................................................................................................................................... 4

2. LOCATION ................................................................................................................................... 5

3. GEOLOGY ................................................................................................................................... 5

4. SCOPE OF WORK ....................................................................................................................... 5

5. PURPOSE AND OBJECTIVES OF PROCESSING ...................................................................... 7

6. ACQUISITION .............................................................................................................................. 8

6.1 ACQUISITION PARAMETERS ......................................................................................................................... 8

6.2 PROCESSING SEQUENCE ............................................................................................................................ 9

7. PROCESSING AND PARAMETER TESTING ............................................................................ 10

7.1 GAIN RECOVERY ...................................................................................................................................... 10

7.2 MINIMUM PHASE CONVERSION .................................................................................................................. 10

7.3 DENOISE ................................................................................................................................................. 10

7.4 FILTERING, STATICS AND VELOCITIES ........................................................................................................ 10

7.5 DECONVOLUTION ..................................................................................................................................... 11

7.6 AMPLITUDE ADJUSTMENT .......................................................................................................................... 11

7.7 VELOCITY ANALYSIS (2ND PASS) ............................................................................................................... 11

7.8 PSTM/PSDM.......................................................................................................................................... 12

7.9 VELOCITY MODEL UPDATES ....................................................................................................................... 12

7.10 PRE-STACK AUTOMATIC GAIN CORRECTION (AGC) ..................................................................................... 15

7.11 STACK ..................................................................................................................................................... 15

8. FINAL PRODUCTS .................................................................................................................... 15

9. RECOMMNEDATIONS............................................................................................................... 18

9.1 PROCESSING ........................................................................................................................................... 18

9.2 INTERPRETATION ...................................................................................................................................... 18

9.3 ACQUISITION ............................................................................................................................................ 18

10. CONCLUSION ............................................................................................................................ 19


Figures

Figure 1: Amadeus Basin, Northern Territory ....................................................................................... 4

Figure 2: 2013 Amadeus 2D survey highlighted in blue lines covering Santos operated acreage ........ 5

Figure 3: Amadeus basin stratigraphy with the primary reservoir target, Heavitree Quartzit, highlighted

in the red circle. ................................................................................................................................... 6

Figure 4: Seismic line AMSAN13B-04, selected as best line for PSDM trial due to Murphy 1 well

control, good quality data zones, poor quality data zones and diapiric features. .................................. 7

Figure 5: Lithological interpretation of AMSAN13B-04 trial section (based on Pre Stack Time Migration

data) .................................................................................................................................................... 8

Figure 6: Initial stacking velocity for the first pass of PSTM ................................................................ 12

Figure 7: Initial interval velocity model ................................................................................................ 13

Figure 8: Adapted RMS velocity model for PSTM .............................................................................. 13

Figure 9: Interval velocity model for PSDM ........................................................................................ 14

Figure 10: Residual interval velocity correction for final PSDM........................................................... 14

Figure 11: Final interval velocity model for PSDM .............................................................................. 15

Figure 12: PSTM stack using the final velocity model ....................................................................... 16

Figure 13: PSDM stack using the final velocity model ........................................................................ 16

Figure 14: the original stack of AMSAN13B-04 (A) in comparsion with the final PSTM stack (B) and

PSDM stack (C) ................................................................................................................................. 17

Figure 15: 1D modelling of optimal acquisition parameters …………………………………………….. 17

Tables

Table 1: Acquisition parameters used in the 2013 Southern Amadeus 2D survey………………..…….7

Table 2: Recommended recording parameters for future acquisition in the Amadeus Basin…………18


1. INTRODUCTION

1.1 Scope of report

This report describes the Pre Stack Depth Migration (PSDM) trail undertaken on seismic line AMSAN13B 04 in the Amadeus Basin, Northern Territory (Figure 1).

Figure 1: Amadeus Basin, Northern Territory


2. LOCATION The 2013 Amadeus 2D survey, of which the trial line AMSAN13B 04 is part, covered in this report is located in the Amadeus Basin and covers a number of Santos operated permits (Figure 2).

Figure 2: 2013 Amadeus 2D survey highlighted in blue lines covering Santos operated acreage

3. GEOLOGY The intracratonic Neoproterozoic to early Carboniferous Amadeus basin occupies much of the southern quarter of the Northern Territory and extends about 150km into Western Australia, covering about 170,000 sq. kms. It has a maximum sediment thickness of 14 km. The primary reservoir target is the pre-salt Heavitree Quartzite (Figure 3), with source thought to be provided by the lower Gillen Member. Only two wells in the basin have penetrated the pre-salt play, with both achieving He-rich gas flows from this interval. Magee-1 flowed gas from fractured Heavitree Quartzite. Mt Kitty 1 flowed gas from fractured granodiorite basement, as the Heavitree Quartzite was absent. Low porosity (no matrix porosity and <2% fracture porosity) in the fractured basement play indicates that the Heavitree Quartzite is required to achieve economic volumes.

4. SCOPE OF WORK Santos acquired 1564km of regional 2D seismic in 2013 (AMSAN13B survey) as the first phase of exploration in the basin. While some of the data was excellent quality, in areas of halotectonics, the data quality deteriorates significantly. Given the primary target of this exploration programme is the sub-salt Heavitree Quartzite, it is imperative that the imaging of areas of the sub-salt and intra-salt packages be improved. A PSDM

AMSAN13B 04


trial has been undertaken to determine if pre stack depth migration can improve the imaging of these packages.

Figure 3: Amadeus basin stratigraphy with the primary reservoir target, Heavitree Quartzit, highlighted in the red circle.


5. PURPOSE AND OBJECTIVES OF PROCESSING The PSDM trail was undertaken in-house with several key drivers: Prospectively assessment: several weak leads have been identified from a combination of regional seismic interpretation (largely using the AMSAN 13B survey) and gravity data (filtered bouguer gravity). In areas of poor data quality, confidence in the basement pick (base reservoir) is low. Improved confidence in the basement pick would increase the probability of closure for these key leads across the basin. Planning for Phase 2 seismic: Phase 2 of the Southern Amadeus seismic programme requires acquisition of 1300 km of infill 2D seismic. This seismic is intended to mature leads to drill ready stage, which may then be drilled as Phase 3 of the programme. If the PSDM trial looks encouraging, then seismic acquisition may be planned in areas of currently poor data quality, such as in north of EP 82 with the knowledge that seismic processing can assist in imaging the base reservoir. Processing of Phase 2 seismic: If the PSDM trial results in a significant improvement in the sub-salt imaging, then it may be incorporated in the processing work flow for key lines of the Phase 2 seismic programme. This PSDM trial may also assist in confirming that the acquisition parameters planned for use in the Phase 2 seismic program are appropriate. Seismic line AMSAN13B-04 has been selected for the trial given it combines zones of both good quality and poor quality data, diapiric features and well control via Murphy 1 (Figures 4 and 5).

Figure 4: Seismic line AMSAN13B-04, selected as best line for PSDM trial due to Murphy 1 well control, good quality data zones, poor quality data zones and diapiric features.


Figure 5: Lithological interpretation of AMSAN13B-04 trial section (based on Pre Stack Time Migration data)

6. ACQUISITION Below is a summary of acquisition parameters used during the Southern Amadeus 2D survey undertaken in 2013 (Table 1).

6.1 Acquisition parameters

Table 2: Acquisition parameters used in the 2013 Southern Amadeus 2D survey

General Parameters Southern Amadeus 2D 2013 survey

Acquisition contractor TERREX Seismic crew 403

Original client SANTOS

Date acquired August-November 2013

No. 2D lines 14

Line km 1600 Line km

No. channels per shot record 480

Nominal stacking fold 240

Recording array Symmetrical Split spread,

Nominal offset range 5987.5– 12.5 – x – 12.5 – 5987.5 m

Correlated record length 5 secs

Recorded sample interval 2 ms

Source interval 25m

Receiver interval 25m

Bin size 12.5m

VP and Receiver numbering Increment 1

Source Parameters

Source type Vibroseis


6.2 Processing Sequence

Below is a detailed summary of the processing sequence undertaken for the 2013 2D survey in the Amadeus basin. Pre-PSDM Processing Sequence Pre-processing

Geometry creating, using SPS-files.

Line binning.

Gain recovery using Spherical Divergence Correction (TV2).

Vibroseis: minimum phase filter application (Sweep dependent).

Whole offset range first break picking Denoise

Frequency dependent Surface Wave Noise Attenuation (SWNA) in CDP domain, 1 pass.

Frequency dependent SWNA in receiver domain, 1 pass.

Adaptive ground roll attenuation (fan filter) in shot domain, 1 pass.

Adaptive ground roll attenuation (fan filter) in receiver domain, 1 pass.

Frequency dependent SWNA (FDNAT) in shot domain, 1 pass. Statics

2D refraction statics modelling (to 500m datum).

Statics correction to floating datum plane.

Velocity analysis every 1000m using refraction statics – V1 velocity

Surface consistent Deconvolution

Spike deconvolution, Operator length 120ms, window 200ms -3000ms

Surface consistent FB statics instead residual statics. Amplitude adjustment

Surface consistent amplitude correction, window 400ms - 3500ms (source, receiver and offset terms applied)

Velocities and Dip Move Out Correction

Velocity analysis every 500m using 2D refraction statics – V2 velocity

Frequency dependent SWNA in offset domain, 1 pass.

Forward and Reverse DMO

Dip move out correction and bin harmonization in 25m offset classes. Migration

PSTM Migration in GEODEPTH

Migration velocity analysis

Kirchhoff migration using smoothed migration velocities,

Vibrator type I/O AHV 4

Vib Control VE464

Number of Vibrators 3 Vibes Inline.centred on half station, 70% force

Sweep frequency 5-90Hz,8-80Hz,10-80Hz,10-82Hz & 12-80Hz

Sweep type Linear

Sweep length 12 secs

Number of sweeps per VP 1

Front & Back – end tapers 500 msec/ 300msec

Instrumentation

Recorder Sercel SN428

Filters Hi cut 0.8 Nyquist Linear Phase Low cut out

Data Format SEG-D

Auxiliaries TB,100Hz,Pilot,DPG Ref, Sweep Auto-Correlation


PSTM stack using final outer XT stacking mute

PSDM Migration in GEODEPTH

Migration velocity modelling

PSTM Migration velocity modelling: Stacking Velocity to RMS velocity

2D PSTM isotropic Kirchhoff migration velocity modelling

Interpretation of PSTM stack, creating geological model for PSDM

Migration velocity modelling RMS velocity to interval velocity model

2D Kirchhoff Eikonal DEPTH migration using smoothed initial interval velocity model

Interpretation of PSDM stack, creating geological model for residual correction

Creating of final velocity model, residual velocity correction

Final 2D Kirchhoff Wavefront DEPTH migration using final velocity model.

Pre-stack AGC (Gate 1000ms)

Final PSDM stack using final velocity model

7. PROCESSING AND PARAMETER TESTING Outlined below is the processing and parameter testing undertaken on seismic line AMSAN13B-04 for the PSDM trial.

7.1 Gain recovery

The loss of amplitude as a function of time is a result of several factors such as geometrical spreading

of the wave front, absorption of the signal and conversion into S-waves. Therefore, 𝑇𝑉2 spherical divergence correction was applied to the data.

7.2 Minimum phase conversion

One of the requirements for Wiener-Levinson deconvolution is for the input data to be minimum phase. To convert the data to minimum phase a phase-shift filter that will convert the Klauder wavelet into its minimum phase equivalent must first be derived. The Klauder wavelet is the autocorrelation of the pilot sweep, the effective source pulse. The calculated phase-shift filter is then applied to the seismic data to convert it to minimum phase.

7.3 Denoise

De-spiking: Automatic statistical trace editing is carried out to detect and remove spikes, high amplitude noise bursts and noisy traces. Spikes were replaced by interpolated data and noise bursts were scaled down to expected levels or edited based on a threshold value. Frequency dependent noise editing: Promax module SWNA was used to edit denoise effects. SWNA attenuates high amplitude noise in decomposed frequency bands. It uses frequency-dependent and time-variant amplitude threshold values in defined trace neighbourhoods to detect and suppress noise specific to different frequency ranges and different times.

7.4 Filtering, Statics and Velocities

Ground roll was the challenge for this dataset. Fan filtering (adaptive ground roll attenuation) was used for the linear noise attenuation. Brute stacks were created using elevation statics correction only. First break (FB) picking is undertaken using an automatic FB picker with hand correction. Refraction static modeling involves both inputs of picked FB times from shot records and an initial near surface velocity together with scanning near surface control points at discrete locations. It


defines weathering thickness and velocity in the initial model through point to point. This allows the building of a smooth near surface velocity model for the whole line; defining the number of refractors in the model and computing arrival times that would occur if this earth model was correct. Statics are then calculated for the optimized model using its velocities and refractor depths. Refractor replacement velocities have been used from the base of the refractor to the processing datum. This was done interactively with proper control, point by point. A replacement velocity of 3000m/sec was used to correct from the base of the weathering to a flat 500m datum. Velocity analysis (1st Pass): Velocity analysis was undetaken every 1 km using the refraction statics solution.

7.5 Deconvolution

A surface consistent deconvolution was used to remove the filtering effects of the earth. The deconvolution compresses the wavelet and increases the resolution of the data. It is also designed to remove reverberations and multiples in the data. In surface consistent deconvolution each trace is expressed as the combination of the convolution of the earth’s reflectivity series with four filters characterized respectively by the shot point position, the receiver position, the CDP, geology and the shooting distance. The same source filter is used for traces belonging to the same shot point and, similarly, one receiver filter is used for traces belonging to the same receiver position. Multi-channel surface consistent deconvolution using a Spike operator (length 120ms and design window 200ms – 3000ms with zero phase output) was applied.

7.6 Amplitude adjustment

Surface consistent gain corrections were used to correct for high frequency spatial variations in the trace amplitude that are due to surface coupling (both vibrator and geophone coupling) and to varying near-surface ground conditions. Spatial amplitude variations have two components:

A low frequency regional component caused by the geology; and

A high frequency component due to variations in source and receiver coupling. Correction for high frequency amplitude variations involved two phases:

An offset term correcting for regional amplitude decay with increasing offset; and

A surface consistent term correcting for the high frequency component. Surface consistent amplitude correction was computed and applied after the surface consistent deconvolution and 1st pass surface consistent residual statics. An amplitude vs. offset gain curve was derived and applied before suface consistent amplitude corrections for source and receiver were calculated using time window 200ms – 3500ms.

7.7 Velocity analysis (2nd Pass)

Second pass velocity analysis was undertaken every 500 m. This was undertaken in both the CDP and offset domains. Frequency dependent SWNA in CDP domain:

Linear noise attenuation (for noise bursts) was performed in the CDP domain where alternate CDP gathers were flipped back-to-back.


Frequency dependent SWNA in offset domain:

Linear noise attenuation (also for noise bursts) to improve S/N ratio was performed in the offset domain by sorting the data in offset classes.

DMO & Bin Regularisation:

2D regularization and trace interpolation

2D regularization and trace interpolation was tested in offset classes. The data was divided in 240 offset classes with an interval of 25m.

The dip move out was reversed prior to PSTM and PSDM. Radon Multiple Removal: Radon multiple removal typically removes multiples characterized as events with a slower velocity than the primary events. Testing comprised identifying the ideal difference in move-out between multiples and primaries.

7.8 PSTM/PSDM

Migration velocity analysis: Migration velocity analysis was done in the time, time migrated and depth domains.

7.9 Velocity model updates

Migration velocities were updated in a step by step fashion from initial stacking velocity through to the final interval velocity model (Figures 6, 7, 8, 9, 10 and 11) under control of geological model. After the first iteration of PSDM production the migration velocity field was removed and velocities were repicked in order to improve the stacking response. This was done with high density automatic velocity picking using horizon velocity spectrums with the geological model.

Figure 6: Initial stacking velocity for the first pass of PSTM


Figure 7: Initial interval velocity model

Figure 8: Adapted RMS velocity model for PSTM


Figure 9: Interval velocity model for PSDM

Figure 10: Residual interval velocity correction for final PSDM


Figure 11: Final interval velocity model for PSDM

7.10 Pre-stack automatic gain correction (AGC)

Final PSTM stacks was created with pre-stack AGC. Pre-stack AGC gates applied were 1000ms, time 0ms-5000ms.

7.11 Stack

A stacking mute (as shown below) was applied

Time (ms) Offset (m)

0 165

333 590

626 1365

1116 2257

2000 3240

2750 6000

The data was stacked using 1/n stack compensation. The nominal fold was 240. Static correction to the final datum was made by applying the regional CDP floating datum statics component. The final datum for all datasets is 500m with a replacement velocity of 3000m/s. A post stack bandpass filter 5-8-80-100 Hz was applied. No post-stack scaling was applied as no improvement was noticed.

8. FINAL PRODUCTS The following SEGYs for the line were archived:

PSTM full stack (Figure 12)

PSDM full stack (Figure 13)


A comparison of all three versions is shown in Figure 14

Figure 12: PSTM stack using the final velocity model

Figure 13: PSDM stack using the final velocity model


A)

C)

B)

Figure 14: the original stack of AMSAN13B-04 (A) in comparsion with the final PSTM stack (B) and PSDM stack (C)


9. RECOMMNEDATIONS

9.1 Processing

Processing is complicated by the variable geology in both the shallow and deeper sections. It is recommended that in future processing, the following be taken into consideration:

Static solutions must be resolved point by point. This could be accomplished by having high density 2D data or using uphole data.

Close attention should be paid to amplitude gain due to the variable surface and deep geology, the large scattering effects on the steep dip, faults and unconformities.

Variable deconvolution must be applied due to very variable surface and deep geology.

Intensive diffraction waves in all directions need to be preserved during linear noise attenuation, as this will help to get the best images after PSTM and PSDM.

Intrinsic absorption is not a major problem, however low frequency should be preserved to ensure quality imaging of the basement.

As a result of the high velocities in the section, clear and coherent gathers are required.

Velocity variations and steep dips mean that the final TWT or depth geometry is very sensitive to the velocity models.

A variable mute is required along the line.

9.2 Interpretation

Phase to phase interpretation looks difficult due to the complex nature of the geology (multiple unconformities etc), length of the line and absence of well data. Picking of the intermediate elements (channels, unconformities, inter salt layers etc) is the most complicated challenge and requires additional iterations between processing and interpretation. PSDM is a good method for time to depth conversion. It will be most effective under a controlled geological model with adequate well control. The complicated geology may require a number datasets for interpretation, including angle and offset stacks.

9.3 Acquisition

Figure 15: 1D modelling of optimal acquisition parameters


The folliwng table provides an overview for the recommended recording parameters for any future acquisition in the Amadeus Basin. The recording of raw uncorrelated data is required. Table 2: Recommended recording parameters for future acquisition in the Amadeus Basin

10. CONCLUSION The AMSAN13B-04 PSDM trial has been effective and furthered the understanding of the complicated Amadeus Basin geology and its implications for future acquisition and processing. The primary objective was to improve the confidence in the basement pick. Some improvement was obvious along the line, as well as improvement within the intermediate structural elements. This trial has largely improved the understanding of preferred processing and acquisition parameters. An opportunity now exists to apply the learnings from this trial on any future acquisition in the Amadeus Basin.

Recommended Parameters

No. channels per shot record 700-1500 Depending on recording system

Nominal stacking fold 350-375

Recording array Symmetrical Split spread,

Nominal offset range 7000(7500) – x – 7000(7500) m

Listening length 5 secs

Recorded sample interval 2 ms

Source interval 10-20 m

Receiver interval 10-20 m

Bin size 5-10

Source Parameters

Source type Vibroseis

Vibrator type I/O AHV 4

Vib Control VE464

Number of Vibrators 3 Vibes Inline.centred on half station, 60-80% force

Sweep frequency 6(8)-80(90)Hz

Sweep type Linear

Sweep length 10-16 secs

Number of sweeps per VP 1

Front & Back – end tapers 250 msec/ 250msec

Instrumentation

Recorder Sercel SN428/FairField Nodal

Filters Hi cut 0.8 Nyquist Linear Phase Low cut out

Data Format SEG-D, SegY

Auxiliaries TB,100Hz,Pilot,DPG Ref, Sweep Auto-Correlation

Recording Correlated and uncorrelated gathers*

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