4D seismic monitoring using horizontal wells – A synthetic case study from Troll by Eva Janská (formally: TU Delft, recently: Statoil) S. A. Petersen (Statoil), G. Toxopeus (Statoil)

1. 4D seismic monitoring using horizontal wells
– A synthetic case study from Troll –
Eva Janská (formally: TU Delft, recently: Statoil)
S. A. Petersen (Statoil), G. Toxopeus (Statoil)

2. We have been looking at the possibility of monitoring the gas-oil contact movements by
seismic acquired in the horizontal well, in case that the sources and receivers are mounted
to the well completion.
Gas
Oil
Water
Copy: Amerex Corporation
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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3. Presentation Outline
First Feasibility Study on
• Where?
Frequent
• How?
4D Monitoring
of Gas-Oil Contact
• Results
(GOC)
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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4. Troll Field – West Oil • Geology
− Semi-horizontal layers
− Calcite cemented zones of uncertain extend
• Thin oil layer with a gas cap and continuity
• Oil produced by multi-branched horizontal wells − 2 types of reservoir sands
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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5. 2D Velocity Models Simulating Oil Production in Troll
Velocity difference
due to oil production
Original GOC
GOC Drawdown
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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6. How to Monitor the GOC Movements Frequently?
• Receivers
• Seismic acquisition − In the horizontal part of the well
• Tools fixed in/close to a horizontal well − Close to the target area of GOC
• Source(s)
− Various positions & frequencies
Multi-branch horizontal well in
Troll in schematic subsurface
2nd well branch –
same depth as 1st
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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7. Frequent GOC Monitoring - Investigation Strategy
-> Reservoir Before & After Production
− Velocity models
-> Simulating Seismic Acquisition
− Source(s) & receivers
− Finite-difference approximation of acoustic wave field
− > Synthetic seismograms
-> Evaluation of Results
− Differential seismograms
• More signal ≈ More GOC drawdown
− Interpretation suggestions
− > Optimal acquisition setup
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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8. Seismograms
Original GOC
Frequency [Hz] after oil
GOC production
50 100 500 1 000 5 000 10 000
Position
Frequency [Hz]
50 100 500 1 000 5 000 10 000
Single – Horizontal well
Position
Differential seismograms
Multiple – Horizontal well
Single – Horizontal well
Frequency [Hz]
Position MultipleSingle 50 100
– Horizontal zone
– Gas well 500 1 000 5 000 10 000
Multiple – Gas zone
Single – Gas zone
Single – Horizontal well
MultipleHeel of zone
– Gas horizontal well
Multiple – Horizontal well
Heel of Heel of horizontal well
horizontal well
Single – Gas zone
– Large velocity model
Multiple – Gas zone of horizontal well
Heel
– LargeSea bed model
velocity
Heel of horizontal well
Sea bed
Heel of horizontal well
– Large velocity model
Sea bed
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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9. Results
… The most advisable source delivers the most precise and demonstrable information about
the GOC shape after oil production and its distance from the well…
• Best setup: • Most economic setup:
− Multiple source in horizontal wells − Source in heel of well
− 1000 Hz Ricker wavelet − 100 Hz Ricker wavelet
− Easier to interpret  Harder to implement − Easier to implement  Harder to interpret
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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10. Multiple Source in Horizontal Well – 1 000 Hz
~ plane wave
well
time
Seismogram – GOC after oil production
• GOC indication on differential ~distance to well
seismogram:
− Direct
− Delay in reflections
• Also with the OWC movements
Differential Seismogram – effect of oil production
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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11. 100 Hz Source at Heel of Horizontal Well
• Complex origin of the time delay in signal:
− Snapshots from the wave field with original GOC (A) and from the ‘differential’ field (B)
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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12. 100 Hz Source at Heel of Horizontal Well
Differential Seismogram – effect of oil production
well
Max GOC drawdown
time
Max differential signal
Max differential signal far
behind max GOC drawdown.
Differential signal assigned to
the centre of source-receiver:
• Shape coincidance with GOC
 Calibration required
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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13. Conclusions
4D seismic monitoring using horizontal wells
- A synthetics case study from Troll -
Numerical simulations show that monitoring the gas-oil contact by a seismic acquisition,
where the tools are fixed in horizontal wells,
is feasible.
Most favourable source positions for the GOC monitoring:
• Proved by simulations – Multiple sources in the horizontal well
• First to be implemented – At heel of the well & sea surface
Geological setting:
• Not a crucial aspect (in horizontally layered reservoir)
• Reflective layers
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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14. Acknowledgments
• Statoil for the internship opportunity.
• Jan Thorbecke (TU Delft) for executing elastic simulations of some of my models.
• Guy Drijkoningen (TU Delft), Norunn Skjei (Statoil) and Kristian Gjerding (Statoil) for
their help and concern during the project.
4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Eva Janska, S. A. Petersen, G. Toxopeus
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15. Questions & Answers
Thank you for attention !

16. 4D seismic monitoring using horizontal wells – A synthetic case study from Troll
Classification: Internal 2010-05-03
2010-06-11Classification: Internal 2010-05-03
Eva Janska, S. A. Petersen, G. Toxopeus
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