4D processing pilot over Umm Shaif shallow marine …...The processing :4D Qcs, difference sections 183551-MS • 4D Processing Pilot over a Giant Carbonate field, Offshore UAE •

4D processing pilot over Umm Shaif shallow marine carbonate field

A. Lafram*;P.F Serieys**; Christian Hubans*; XXXX***

* Total E&P

** CGG

*** ADMA

Time lapse seismic is a proven technology for reservoir monitoring. It allows accessing useful

information about the fluid movement, pressure changes and so on. But, this technology has still

some limits in term of area of application. Shallow marine Middle East carbonate reservoirs is one of

them.

In order to test this limit, ADMA performed a 4D pilot (OBC/OBC) over the Umm Shaif field, where

the 2013 monitor has repeated the geometry of 1994 base (parallel shooting). In this paper, we

describe the challenges of the 4D processing of this data, the applied solutions and some results.

The water bottom over the pilot area ranges from 15 to 25 m. The main challenges of this 4D

processing are:

- Geometry errors in the legacy OBC data: they have negligible impact in 3D but they increase

the 4D noise. Significant time was spent correcting these errors.

- Noise contamination: the 2C component over the area is highly contaminated by Scholte

waves and guided waves. Additionally, the geophone of the monitor data was highly

impacted by current noise. It was necessary to bring the hydrophone and geophone to a

satisfactory S/N before summation, in order to derive reliable operator for PZ summation

(Figure 1). One important point for this 4D project was to favor the less statistical and less

adaptive process.

- Multiple attenuation: in 4D, the multiple can be highly non repeatable because of changing

sea water conditions. The area is known for its severe contamination of short period

multiples due to shallow marine hard sea bottom environment. After PZ summation, an

optimized 3D deconvolution was performed (Figure 2 ) .

- 4D time and amplitude destriping: it was important to remove the distortion due to different

acquisition conditions, coupling etc. Using a robust S/N separation before deriving time shit

and scalar correction was a key in order to minimize 4D noise.

The data integrity analysis and correction, the optimal denoise and demultiple, the careful attention

paid to the acquisition-related distortion removal as well as adapted 4D QCS all along the

processing sequence allowed to obtain an interpretable 4D signal which gives useful information

about the reservoirs.

These successful results were made possible by a careful control of the noise and multiple

attenuation, favoring the use of the deterministic and constrained processes over the adaptive

processes even if these latter may be superior in 3D processing; and a robust S/N separation in the

4D crossequalisation/parallel processing were designed and applied. These elements enabled to get

an interpretable 4D signal under the very challenging conditions of the considered area and

reservoirs.

Figure 1 : Example of CMP gathers before/after pre PZ summation denoise

Figure 2 : Example of base and monitor inline before/after shallow water demultiple

HOSTED BY:

SUPPORTED BY:

1

183551-MS4D Processing Pilot over a Giant Carbonate

field, Offshore UAE

Abderrahim LAFRAM , TOTAL

Pierre Francois SERIEYS, CGG

Christian HUBANS, TOTAL

Ahmed SAEED AL KAABI, ADMA-OPCO

Marc BENSON, ADMA-OPCO

2

Introduction

Why 4D monitoring is challenging in offshore UAE ?

The acquisition description

The processing

Outline

Main challenges and solutions 4D QCs

Some interpretation elements

Conclusions

183551-MS • 4D Processing Pilot over a Giant Carbonate field, Offshore UAE • A.Lafram3

Introduction



The processing

Outline



Conclusions


Time lapse seismic is a proven technology for reservoir monitoring

Using repeated seismic, it allows to obtain useful information about : fluid saturations changes, pressure changes , stress changes

Widely used in North sea, West Africa, GOM but very few applications

Introduction

Widely used in North sea, West Africa, GOM but very few applications in Middle East carbonate fields

A pilot was designed by ADMA-OPCO to test this technology in Offshore UAE ( shallow marine survey 15-25 m)


Introduction



The processing

Outline



Conclusions


Why 4D monitoring is challenging in Offshore UAE ?

Raw hydrophone After denoise + Pz summation

183551-MS • 4D Processing Pilot over a Giant Carbonate field, Offshore UAE • A.Lafram

After shallow water demultiple and denoiseFinal gathers

Same amplitude scale ! 7

Surface conditions

Shallow marine with hard water bottom and strong shallowreflections : extreme contamination of sholte waves, guidedwaves and multiples

Noise ( multiples, coherent and ambient noise) much higher energythan the desired « signal »

In 4D context, this noise has to be removed in a consistent way in

Why 4D monitoring is challenging in Offshore UAE ?

In 4D context, this noise has to be removed in a consistent way in base and monitor

Reservoirs configurations

Heterogeneous reservoirs, changing porosity, changing facies Rock physics in carbonate not fully understood


Some interpreted production phenomena

WOC Rise-up

Re-pressurization

Gas cap expansion


Despite the challenging surface and reservoir conditions, it was possible to interpret some very useful information about the reservoirs

Gas re-dissolution

Sea water vs. BrineDIp/Ip

9

Introduction



The processing

Outline



Conclusions



Vintage Base Monitor

Ocean Bottom Cable

Cable Spacing 300m 300m

Receiver Int. 50m 25m

P-Z (2 compon.)

P-Z-X-Y (4 compon.)

Maximum Offset 3000m 10145m to be cut to 3000

BaseMonitor


Active cable number /SP 2 3

Source

Operating Pressure 2000psi 2000psi

Total Volume 1500 cu in 2740 cu in

String Separation 10m 5m

Array Length 15.6m 12m

Source Line Spacing 50m 50m

Shot Int. 25m 25m

Number Source Lines / Patch 12 24

Source Depth 3m 5m

Receiver

Shot

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Shot (in red) and receiver ( in black )positions

Monitor Base

12



4D repetablity GeometryDSR = DS + DR


Monitor Base

13


Offset 500 m Offset 1500 m Offset 2500 m


Geometry repeatability dsdr

0 m 150 m



Monitor Base

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Offset 500 m : 62 % traces with dsr <20 m ; 90 % of traces with dsr <50 m Offset 2500 m : 55 % traces with dsr <20 m ; 87 % of traces with dsr <50 m


Offset 500 m Offset 1500 m Offset 2500 m


Geometry repeatability dsdr

0 m 150 m



Monitor Base

Except in the obstructions , the geometrical repeatability is good

15

Offset 500 m : 62 % traces with dsr <20 m ; 90 % of traces with dsr <50 m Offset 2500 m : 55 % traces with dsr <20 m ; 87 % of traces with dsr <50 m

Introduction



The processing

Outline



Conclusions


Main challenges :

Geometry errors for the legacy data

Noise contamination

Ocean Bottom Cable measurements ( Geophone and hydrophone ) : different noise characteristics

High contamination of guided and sholte waves

The processing

High contamination of guided and sholte wavesHigh contamination of seabed current noise ( especially the monitor)

Multiples ( non repeatable ? )

Acquisition related time and amplitude distortions

4D QCs :

Optimal 4D results # 2 optimal 3D processings: The processing steered by 4D QCs


The processing : Denoise before summation

Progressive and targeted noise attenuation , different collections ( data sorting) and combining different techniques


Geophone raw Geophone input to PZ sum

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Bring Geophone and Hydrophone to the best and the most similar SNR to combine them robustly in the PZ summation

The processing : Demultiple


Base after Pz sum Monitor after Pz sum Difference after Pz sum

Base after SWD Monitor after SWD Difference after SWD

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Multiples ( especially surface related ones) are highly non repeatable


Base Multiples Monitor Multiples

ones) are highly non repeatable between the base and monitor

20

Introduction

Why 4D monitoring is challenging offshore UAE ?


The processing

Outline



Conclusions


The processing :4D Qcs, difference sections


Final 3D image 4D diff after PZ sum 4D diff after SWD 4D diff time and amplitude destriping and denoising

4D diff after regul4D diff after Fast trackFinal 4D diff

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The processing :4D Qcs, NRMS sections

NRMS time and amplitude


Final 3D imageNRMS after PZ sum NRMS after SWD

NRMS time and amplitude destriping and denoising

NRMS after regulNRMS after fast trackFinal NRMS

( )( ) ( )monitorRMSbaseRMS

basemonitorRMSNRMS

+

−=

.2

Good Bad

23

The processing : 4D QCs : SDR=f(NRMS)


SDR

NRMS

Progress in processing

24


basemonitorRMSNRMS

+

−=

.2

The processing : 4D QCs : SDR=f(NRMS)

density


SDR

NRMS

Progress in processing

25


basemonitorRMSNRMS

+

−=

.2

Introduction



The processing

Outline



Conclusions




Very good coherency between 4D signal and expected WOC rise-up areas

27

Some interpretations elements D

Vp

/Vp


Good coherency between dVp/Vp results and the structural scheme

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Vp

Some interpretations elements : interpretation summary

4D Signal in the reservoir is:

Coherent with structural scheme Coherent with dynamic data from wells (gas/water production, …) Coherent with phenomena expected by the reservoir model

As a main point, water rise-up is recognized, and the top water surface at monitordate can be picked


date can be picked

Barrier role at an identified level in the reservoir level is well expressed on 4D data

Other production phenomena (expected from dynamic model) like re-pressurization, gas re-dissolution, gas cap expansion can be interpreted on 4D

29

Introduction

Why 4D monitoring is challenging offshore UAE ?


The processing

Outline



Conclusions


Conclusions

This experiment shows that 4D seismic in carbonates offshore UAE with difficult seismic environment is possible under some acquisition repeatability conditions and by designing and conducting processing carefully

The data integrity QC and correction, the extensive denoise sequence, the demultiple as well as the correction of acquisition related distortions were necessary to reveal the 4D signal


necessary to reveal the 4D signal

The systematic 4D QCs are mandatory to steer the processing

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Acknowledgements

Abu Dhabi Marine Operating Company (ADMA-OPCO) for designing and conducting this experiment and for the authorisation to publish this work

Total for supporting this work


Total for supporting this work

Jean Luc PIAZZA from Total and Jean Louis RIVAULT from CGG for the fruitful interactions and Frederic CAILLY, Adeoye ADEYEMI and Tarek AL ROMANI from Total for their elegant interpretation and interactions

32


Thanks/Questions

33


Back up

34

The multiples can be highly non repeatable : if not removed optimally, they hide and distort the 4D signal

OBC dual sensor measurement : combination of Hydrophone and Geophone allow to attenuate the ghost and the water layer reverberations


Residual water layer reverberations as well as the multiples generated by other shallow reflections are tackled by Shallow Water Demultiple ( prediction of multiples followed by subtraction )

Adaptive subtraction tested for benchmarking but not used


The base data has some errors in the geometry

The impact of these errors : little in 3D imaging , significant in 4D

The solution used : refraction travel time analysis

The processing : Legacy geometry correction


Changes in tide elevations, water velocity Time distortion Emitted Source signal and sensors response Amplitude distortion

The processing : acq related time and amplitude distortion correction

These distortions must be corrected to reveal the production related 4D

Time shift overburden


to reveal the production related 4D

Before correction After correction


Base after Pz sum Base after SWD


Base after Pz sum

Monitor after Pz sum

Base after SWD

Monitor after SWD

Multiples Base Multiples Monitor

The multiples ( especially surface related ones) are highly non repeatable between the base and monitor

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The pilot processing :4D Qcs, SDR maps ( reservoir window)

2

)),((2

max monitorbaseCCSDR

−=


Good Bad

)),((2

max1 monitorbaseCCSDR

−=

after PZ sum after SWDAfter time and amplitude destriping and denoising

after regularisation after fast track Final

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The processing sequence

Geometry Qc and correction

Cold water & Cold water &

Base Monitor

Zero-Phase Zero-Phase

Geometry Qc

Guided waves , Scholte waves attenuation

Swell noise and seabed current noise attenuation

Pz summation and Shallow water demultiple

Guided waves , Scholte waves attenuation

Swell noise and seabed current noise attenuation

Pz summation and Shallow water demultiple


4D Binning

High Density Velocities HR radon demultiple

Foot print attenuation Random Noise attenuation

Migration Migration

Cold water &Tidal Statics

Cold water &Tidal Statics

Global Matching

Global Matching

Regularisation and denoise

4D time and amplitude destriping

High Density Velocities HR radon demultiple

Foot print attenuation Random Noise attenuation

40

Regularisation and denoise

Documents

4D processing pilot over Umm Shaif shallow marine …...The processing :4D Qcs, difference sections 183551-MS • 4D Processing Pilot over a Giant Carbonate field, Offshore UAE •