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Assessing uncertainty of time-lapse
seismic response due to geomechanical
deformation
Doug Angus,
School of Earth & Enviro...
Outline
• Context
• Multi-physics solution
• Time-lapse seismics/geomechanics
• Overburden imaging
• Valhall example
• Geo...
Context
Sleipner
• Negligible pressure effect
• High porosity/high permeability
Snohvit/In Salah
• Pressure effect
• Snohv...
4
e.g., microseismicity – static velocity model
Event location SI Event location MTMIWaveformsVelocity model
e.g., microseismicity – non-static velocity model
Static velocity model
True dynamic velocity model
Event location MTMI
5
• Change in pore pressure (DP)
• Leads to change in horizontal
total stress
• Difficult to predict stress evolution
D ¢sV ...
• Integration (hydro-mechanics):
• Coupled fluid-flow/geomechanics
– Fully-coupled
– One-way coupling (flow to geomechanic...
Stress dependent velocities
Rock physics transforms
8
Reservoir model with high fault transmissibility
Rock physics
Shapiro 2003 Tod 2002
9
Seismic monitoring
Marine seismic
Land seismic
Acquisition (instrument) geometry
10
Time-lapse or 4D seismic
• Change in:
• Saturation
• Pressure/stress
• Mechanical properties
P-wave velocity change for tr...
Time-lapse or 4D seismic
• What is measured:
• Time differences
• Amplitude differences
• “Devil is in the detail”
12
Estimated P-wave reflection amplitude (strength)
changes using full-offset seismic data
Estimated P-wave reflection amplit...
P-wave velocity change for
true earth model
Estimated P-wave velocity
change using full-offset
seismic data
Estimated P-wa...
Time-lapse or 4D seismic
• Tau-p pre-stack approach
15
-7.0
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
1.0
1982 1987 1992 1997 2002 2007 2012
time (year)
subsidence(m)
QP - Measured
QP -...
AVOA modelling
• Map reflection coefficients and
fast P-wave direction
– Using layer-matrix approach
– Elasticity between ...
Microseismicity:
• Valhall reservoir
• Geomechanics and
microseismicity
18
• Likely not all CCS sites will be like Sleipner
• Large scale projects:
– Not always ideal porosity/permeability
– Inject...
• Rock physics transforms
– Models for multiphase fluids, patchy saturation, attenuation, anisotropy,
plasticity
– More da...
21
Valhall reservoir, North Sea
• ELFEN-VIP one-way coupling
– Hexahedra mesh (6 million elements)
– Cap plasticity, non-asso...
Elastic/Elasto-plastic properties
Elastic
Elasto-
plastic
Elastic
Elasto-
plastic
Elastic
23
Microseismicity:
• Weyburn CCS pilot
• Geomechanics and microseismicity
Overburden after production
Overburden after CO2 i...
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Assessing Uncertainty of Time Lapse Seismic Response Due to Geomechanical Deformation, Doug Angus - Geophysical Modelling for CO2 Storage, Leeds, 3 November 2015

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Assessing Uncertainty of Time Lapse Seismic Response Due to Geomechanical Deformation, Doug Angus - Geophysical Modelling for CO2 Storage, Leeds, 3 November 2015

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Assessing Uncertainty of Time Lapse Seismic Response Due to Geomechanical Deformation, Doug Angus - Geophysical Modelling for CO2 Storage, Leeds, 3 November 2015

  1. 1. Assessing uncertainty of time-lapse seismic response due to geomechanical deformation Doug Angus, School of Earth & Environment, University of Leeds, d.angus@leeds.ac.uk Acknowledgements: Claire Birnie, Yanxiao He, Tom Lynch & Dave Price
  2. 2. Outline • Context • Multi-physics solution • Time-lapse seismics/geomechanics • Overburden imaging • Valhall example • Geomechanics and uncertainty • Way forward 2
  3. 3. Context Sleipner • Negligible pressure effect • High porosity/high permeability Snohvit/In Salah • Pressure effect • Snohvit – compartmentalisation • In Salah - ?Top layer 2010 thickness(m) structuralthickness (metres) temporalthickness (msec) 3
  4. 4. 4 e.g., microseismicity – static velocity model Event location SI Event location MTMIWaveformsVelocity model
  5. 5. e.g., microseismicity – non-static velocity model Static velocity model True dynamic velocity model Event location MTMI 5
  6. 6. • Change in pore pressure (DP) • Leads to change in horizontal total stress • Difficult to predict stress evolution D ¢sV = DsV -aDP D ¢sH = DsH -aDP Herwanger (2007) Dynamic view (syn- and post-production) 6 Multi-physics: porous deformable media
  7. 7. • Integration (hydro-mechanics): • Coupled fluid-flow/geomechanics – Fully-coupled – One-way coupling (flow to geomechanics) – Two-way coupling Geophysical attributes D Pp D k, ø, c Stress changes Petroleum Production Reservoir property changes D Si 4D Seismics Microseismics 7 Multi-physics: porous deformable media
  8. 8. Stress dependent velocities Rock physics transforms 8
  9. 9. Reservoir model with high fault transmissibility Rock physics Shapiro 2003 Tod 2002 9
  10. 10. Seismic monitoring Marine seismic Land seismic Acquisition (instrument) geometry 10
  11. 11. Time-lapse or 4D seismic • Change in: • Saturation • Pressure/stress • Mechanical properties P-wave velocity change for true earth model Baseline - Monitor 1 Baseline - Monitor 2 Baseline model 11
  12. 12. Time-lapse or 4D seismic • What is measured: • Time differences • Amplitude differences • “Devil is in the detail” 12
  13. 13. Estimated P-wave reflection amplitude (strength) changes using full-offset seismic data Estimated P-wave reflection amplitude (strength) changes using near-offset seismic data Time-lapse or 4D seismic • Extract time-lapse amplitude changes 13
  14. 14. P-wave velocity change for true earth model Estimated P-wave velocity change using full-offset seismic data Estimated P-wave velocity change using near-offset seismic data Time-lapse or 4D seismic • Extract time-lapse velocity changes 14
  15. 15. Time-lapse or 4D seismic • Tau-p pre-stack approach 15
  16. 16. -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 1982 1987 1992 1997 2002 2007 2012 time (year) subsidence(m) QP - Measured QP - Numerical North - Numerical South - Numerical Vertical displacements predicted vs measured • Subsidence evolution recorded at seafloor • From PO-035105 document – QP (524204,6237070) – North (522181,6242020) – South (527011,6231800) Vertical division of the domain for parallel analysis Horizons surfaces Isosurfaces of vertical displacement 16
  17. 17. AVOA modelling • Map reflection coefficients and fast P-wave direction – Using layer-matrix approach – Elasticity between chosen layers Base Miocene Top Chalk2130ms horizon 17
  18. 18. Microseismicity: • Valhall reservoir • Geomechanics and microseismicity 18
  19. 19. • Likely not all CCS sites will be like Sleipner • Large scale projects: – Not always ideal porosity/permeability – Injection rates and volumes – Fluid-rock (e.g., geochemical) alterations • Must be capable of monitoring strains and overburden effects – Monitor seal integrity – Evaluate CO2 containment Recap 19
  20. 20. • Rock physics transforms – Models for multiphase fluids, patchy saturation, attenuation, anisotropy, plasticity – More data (e.g., shallower depths – overburden) – Calibration with in-situ data (not only core samples) – Scaling (static measurements to dynamic measurements) – significant knowledge gaps, but can apply site specific empirical relationships • Hydro-mechanical models: – Calibration/history match fluid-flow and geomechanical simulation models – Systematic approach to model building (i.e. geometry & meshing) – Constitutive models from rock and petro-physics with up-scaling – Uncertainty of model parameters and geophysical/seismic attributes 20 Challenges, uncertainties & way forward
  21. 21. 21
  22. 22. Valhall reservoir, North Sea • ELFEN-VIP one-way coupling – Hexahedra mesh (6 million elements) – Cap plasticity, non-associated flow rule, water weakening SR3 adjusted to Valhall model (ISAMGEO PO-035105) – Soft coupled to 500,000 grid VIP model – VIP pore pressure output monthly • Pore pressure used by Elfen as applied load • ELFEN solved in parallel (4 domains) • 3 element groups are mapped (VIP-Elfen) – Reservoir Tor – Reservoir Hod – Reservoir faults Overburden Reservoir & Sideburden Underburden Domain partitions for parallel analysis VIP model 22
  23. 23. Elastic/Elasto-plastic properties Elastic Elasto- plastic Elastic Elasto- plastic Elastic 23
  24. 24. Microseismicity: • Weyburn CCS pilot • Geomechanics and microseismicity Overburden after production Overburden after CO2 injection Overburden after shut-off Overburdenfracturepotential Microseismiclocations 24

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