Using rock physicsto reduce seismic exploration risk      on the Norwegian shelf                Per Avseth           Adjun...
Rock physics – the bridge between     geology and geophysics!  Seismic data                                               ...
Outline• The rock physics link = the rock physics  bottleneck• Seismic fluid sensitivity and geological processes• Snap-sh...
3 big challenges in seismic reservoir   characterization using rock physics!• More unknown variables than known observable...
The Rock Physics BottleneckFrom seismic data we can obtain only 3 (possibly 4) acousticproperties: Vp, Vs, density, (and Q...
The rock physics bottleneck: Example from Barents Sea Challenge: More unknowns than independent measurements.            ...
Rock Physics Templates (Ødegaard and Avseth, 2004)1) Increasing shaliness       1) Decreasing effective pressure2) Increas...
Seismic fluid sensitivity          - controlling factors•   Grain contacts (pressure and cement)•   Poreshape and pore sti...
Press and guess! Whats inside the container?Compressibility of dry rock:              1 =       1            φ            ...
Grane versus Glitne reservoir sands                                                                                       ...
SEM images and XRD reveal quartz cement    Unconsolidated                                        Cemented                 ...
North Sea compaction trends of       sands and shales
Couppled rock-physics and diagenesis                             modeling (Helset et al., 2004)          0                ...
Couppled rock-physics and diagenesis                             modeling (Helset et al., 2004)           0               ...
Using rock physics to estimation of cement volume                     (Example from Alvheim Field)                        ...
Cement estimation vs. depth
Bayesian lithology and fluid prediction constrained by spatial          coupling and rock physics depth trends            ...
Estimated depth trends (well 1)
Rock physics model w/uncertaintiesestimated from Well 1 (depth integrated)                         shale                  ...
3-D seismic prediction results   With depth trends   Without depth trends Red=gas   Green=oil
From loose sediments to consolidated rocks – what      happens to fluid and stress sensitivity?            Porosity       ...
4D anomalies; Gullfaks vs. StatfjordPicture 72             Before Water injection After water injection                   ...
Fluid and pressure sensitivity in Gullfaks versus Statfjord Fields              (Duffaut, Avseth and Landrø, 2011)
Troll East time shift analysis                    (Avseth, Skjei and Skålnes, 2012)                                       ...
Geologic overview (schematic), Troll East             Well A             Well B                            Compaction andC...
Shear modulus versus porosity    Sognefjord Formation                                               Contact cement model  ...
Timeshift at GOC                                                                               Seismic observations       ...
Barents Sea; a challenging area due complex        tectonic and uplift episodes             (Ohm et al., 2008)
Compaction trends – 7120/1-2                               CC                                    MC   MC           Torsk  ...
Skalle fluid and facies classification results                (Lehocki, Avseth, Buran and Jørstad, 2012, EAGE Copenhagen) ...
Be aware of scale effects!                             0.63 mm                             2µm
Future of rock physics           (as I see it…)• More integration with basin modeling• Using rock physics trends to constr...
Rock physics modeling of geological processes:From granular rocks to cracked media (Avseth and Johansen, 2012)        Elas...
Ksat and Kdry versus Porosity                 10             x 10         6         5                α = 1.0         4    ...
RPT analysis of tight gas sandstone w/cracks(Bakhorji, Mustafa, Avseth and Johansen, 2012)         2.2                    ...
Conclusions• Rock physics is both a bridge and a bottle-neck between  geophysics and geology.• Better integration with geo...
Let’s rock together! Geologist   Geophysicist
Acknowlegdements• Thanks to Geoforskning.no for the invitation• Thanks to Spring Energy for sponsoring this event• Thanks ...
Upcoming SlideShare
Loading in …5
×

Kan bergartsfysikk og kvantitativ seismisk tolkning bidra til økt funnrate på norsk sokkel?

1,219 views

Published on

av Per Avseth

Published in: Education, Technology, Business
  • Be the first to comment

  • Be the first to like this

Kan bergartsfysikk og kvantitativ seismisk tolkning bidra til økt funnrate på norsk sokkel?

  1. 1. Using rock physicsto reduce seismic exploration risk on the Norwegian shelf Per Avseth Adjunct Professor, NTNU Geophysical Advisor, Odin Petroleum Lunch seminar, Oslo, 22/5-2012
  2. 2. Rock physics – the bridge between geology and geophysics! Seismic data Reservoir geology Qualitative interpretation Rock physics analysis Constant Contact Cement Cement Elastic Modulus Quantitative interpretation of physical rock properties, Friable Initial Sand lithologies and pore fluids Pack 0.30 0.35 0.40 Porosity
  3. 3. Outline• The rock physics link = the rock physics bottleneck• Seismic fluid sensitivity and geological processes• Snap-shot examples from the Norwegian shelf• The issue of scale• The future of rock physics
  4. 4. 3 big challenges in seismic reservoir characterization using rock physics!• More unknown variables than known observables!• Fluid (and stress) sensitivity can vary drastically, not only from one field to another, but within a given field!• What is valid at microscale is not necessarily valid at seismic scale!
  5. 5. The Rock Physics BottleneckFrom seismic data we can obtain only 3 (possibly 4) acousticproperties: Vp, Vs, density, (and Q). Very often we have reliableestimates of only 1 or 2 (AI and Vp/Vs). Seismic Reservoir Rock Physics Properties Attributes Properties Traveltime Porosity Vnmo Vp Saturation Vp/Vs Vs Pressure Ip,Is Density Lithology Ro, G Q Pressure AI, EI Stress Q Temp. anisotropy Etc. etc
  6. 6. The rock physics bottleneck: Example from Barents Sea Challenge: More unknowns than independent measurements.  We need to constrain by local geology! Increasing burial (compaction) Increasing porosity Increasing clay volume Increasing HC saturation
  7. 7. Rock Physics Templates (Ødegaard and Avseth, 2004)1) Increasing shaliness 1) Decreasing effective pressure2) Increasing cement volume 2) Increasing gas saturation3) Increasing porosity
  8. 8. Seismic fluid sensitivity - controlling factors• Grain contacts (pressure and cement)• Poreshape and pore stiffness (e.g. cracks)• Porosity• Mineralogy• Saturation pattern and scale (patchy vs. uniform)• Viscoelastic effects of fluid movement• Relative contrast (cap-rock properties)
  9. 9. Press and guess! Whats inside the container?Compressibility of dry rock: 1 = 1 φ + K dry K mineral Kφ Compressibility of pore space 1 = 1 ∂v pore K φ v pore ∂σ Compressibility of saturated rock: 1 ≈ 1 φ + K +K K sat K mineral φ fluid
  10. 10. Grane versus Glitne reservoir sands Constant Contact Cement Cement Elastic Modulus Constant Constant Contact Cement Contact Cement Cement Fraction (2%) Line Line Cement Fraction (2%) Line Line 3.53.5 Initial Friable SandVp (km/s) Pack Vp (km/s) 0.30 0.35 0.40 3.0 3 Well #2 Grane sst Porosity 2.52.5 Unconsolidated Unconsolidated Glitne sands Well #1 Line Line 0.25 0.3 0.30 0.35 0.35 0.4 0.25 Porosity 0.40 Porosity
  11. 11. SEM images and XRD reveal quartz cement Unconsolidated Cemented Cement rim (Glitne) (Grane) 4000 Si Counts Well #1 Uncemented Well #2 Cemented 2000 C O 0.25 mm 0.25 mm 0 0 2 4 Energy (keV) Back-scatter light Cathode lum. light Grain SEM back-scatter image: Well #2 SEM cathode-luminescent image: 4000 Si Well #2 Counts 2000 O 0.1 mm C 0.1 mm 0 0 2 4 Energy (keV) Qz-grain Qz-cement rim
  12. 12. North Sea compaction trends of sands and shales
  13. 13. Couppled rock-physics and diagenesis modeling (Helset et al., 2004) 0 Exemplar modelling 20 0 (Lander and Walderhaug) 40 0 60 0 Porosity Contact cement model 80 0 Cement volume 4.00 10 0 0 Vp (km/s) 12 0 0 14 0 0 16 0 0 3.00 18 0 0 ep )D th(m 20 0 0 22 0 0 Friable sand model 24 0 0 26 0 0 2.00 28 0 0 0.100 0.200 0.300 0.400 30 0 0 phi (frac) 0 5 10 15 20 25 30 35 R c F ctio s(% o k ra n ) CrePro (% o o sity ) Ma CrePro (% e s. o o sity ) Qa ce e t (% u rtz mn )
  14. 14. Couppled rock-physics and diagenesis modeling (Helset et al., 2004) 0 Exemplar modelling 20 0 (Lander and Walderhaug) 40 0 60 0 Porosity 80 0 Cement volume 10 0 0 12 0 0 14 0 0 16 0 0 18 0 0 e th )D p (m 20 0 0 22 0 0 24 0 0 26 0 0 28 0 0 30 0 0 0 5 10 15 20 25 30 35 R c F ctio s(% o k ra n ) CrePro (% o o sity ) Ma CrePro (% e s. o o sity ) Qa ce e t (% u rtz mn ) Note decreasing fluid sensitivity with depth and diagenesis Ma Qa ce e t (% e s. u rtz mn )
  15. 15. Using rock physics to estimation of cement volume (Example from Alvheim Field) Constant Contact Cement Cement 4500 10 Elastic Modulus 4000 Qz 9 8 3500 Constant cement trendsVs 7 3000 Initial 6 Friable Sand Increasing cement volume Cement volume Pack 2500 5 0.30 0.35 0.40 Vs (m/s) Dvorkin-Nur Porosity 4 2000 contact cement 3 Qz-cement 1500 Picture 2 2 1000 1 500 Shale 0 0 -1 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Porosity Porosity
  16. 16. Cement estimation vs. depth
  17. 17. Bayesian lithology and fluid prediction constrained by spatial coupling and rock physics depth trends (Rimstad, Avseth and Omre, 2012) (Rimstadi
  18. 18. Estimated depth trends (well 1)
  19. 19. Rock physics model w/uncertaintiesestimated from Well 1 (depth integrated) shale Shale Brine sand Oil sand Gas sand
  20. 20. 3-D seismic prediction results With depth trends Without depth trends Red=gas Green=oil
  21. 21. From loose sediments to consolidated rocks – what happens to fluid and stress sensitivity? Porosity Porosity Loose sands: • Large fluid sensitivity (Gassmann theory works well) • Large stress sensitivity (Hertz-Mindlin theory applies) Gullfaks (loose sands) Statfjord (consolidated) Consolidated sandstones: • Reduced fluid sensitivity (Gassmann theory works as long as pores are connected) • Reduced stress sensitivity (Hertz-Mindlin theory does not apply to cemented grain contacts. Dvorkin- Nur ignores stress-sensitive grain contacts)
  22. 22. 4D anomalies; Gullfaks vs. StatfjordPicture 72 Before Water injection After water injection (Duffaut and Landrø, 2007) σ diff ~6 MPa  σ diff ~0-1 MPa Water injector offline Water injector online Top Target σ diff ~15 MPa  σ diff ~6-7 MPa
  23. 23. Fluid and pressure sensitivity in Gullfaks versus Statfjord Fields (Duffaut, Avseth and Landrø, 2011)
  24. 24. Troll East time shift analysis (Avseth, Skjei and Skålnes, 2012) Seismic observations (courtesy of Åshild Skålnes, Statoil) Base Tertiary Top Draupne Cretaceous overburden Top Sognefjord Top FensfjordGas coloumn
  25. 25. Geologic overview (schematic), Troll East Well A Well B Compaction andCompaction depositional trendtrend Draupne Fm GWC Sognefjord Fm Fensfjord Fm
  26. 26. Shear modulus versus porosity Sognefjord Formation Contact cement model 9 x 10 15 Well B Shear modulus (Pa) Diagenesis (east) 10 5 Well A (west) Friable sand model 0 0.1 0.2 0.3 0.4 Porosity
  27. 27. Timeshift at GOC Seismic observations Modelled time shifts (courtesy of Åshild Skålnes, Statoil) 4 6 x 10 1.5 6.745 31/3-S-41 1.2 1.1 6.74 31/3-1 3.5 1 6.735 0.9 1 31/6-6 6.73 dTWT 0.8UTM-Y 3 6.725 Well A 31/6-1 31/6-A-37 (ms) 0.7 Well B 31/6-5 0.6 0.5 6.72 0.5 2.5 31/6-2 31/6-B-6H 0.4 6.715 31/6-8 0.3 25.35 6.71 5.4 1.4 5.45 1.6 5.5 5.55 0.2 0 1 1.2 1.8 2 UTM-X 5 x 10
  28. 28. Barents Sea; a challenging area due complex tectonic and uplift episodes (Ohm et al., 2008)
  29. 29. Compaction trends – 7120/1-2 CC MC MC Torsk Transition Kolmule zone CC7120/1-2
  30. 30. Skalle fluid and facies classification results (Lehocki, Avseth, Buran and Jørstad, 2012, EAGE Copenhagen) Fluids Facies Pre-drill (Myrsildre well only)Post-drill(Skalle well)
  31. 31. Be aware of scale effects! 0.63 mm 2µm
  32. 32. Future of rock physics (as I see it…)• More integration with basin modeling• Using rock physics trends to constrain migration and full waveform inversions• Rock physics of EM, gravity and seismic integrated.• Rock physics of source rocks and unconventionals (practical recipes and computational revelations).
  33. 33. Rock physics modeling of geological processes:From granular rocks to cracked media (Avseth and Johansen, 2012) Elastic modulus DEM HSUB CCT Mineral point alpha=1.0 0.01 0.1 Decreasing aspect ratio Initial contact cement Porosity Critical porosity
  34. 34. Ksat and Kdry versus Porosity 10 x 10 6 5 α = 1.0 4 α = 0.1K (Pa) 3 Wet rock α = 0.01 2 5% contact Dry rock cement 1 0 0 0.1 0.2 0.3 0.4 Porosity
  35. 35. RPT analysis of tight gas sandstone w/cracks(Bakhorji, Mustafa, Avseth and Johansen, 2012) 2.2 0.8 2 0.6 Vp/Vs Brine rock Swt 1.8 0.4 1.6 0.2 Dry rock 1.4 4 6 8 10 12 14 16 AI
  36. 36. Conclusions• Rock physics is both a bridge and a bottle-neck between geophysics and geology.• Better integration with geology can help us constrain the non-uniqeness in quantitative interpretation.• Be aware of the rock type and associated rock stiffness before you look for hydrocarbons using seismic data.• If rocks are well cemented, it can be hard to detect oil from seismic. The oil-window seems to be located around the depth where reservoir sands start to be cemented. In the Barents Sea, the oil window is probably within stiffer rocks than in the North Sea and the Norwegian Sea.• At the end of the day, remember that seismic is the sound of geology!
  37. 37. Let’s rock together! Geologist Geophysicist
  38. 38. Acknowlegdements• Thanks to Geoforskning.no for the invitation• Thanks to Spring Energy for sponsoring this event• Thanks to Statoil and Lundin-Norway w/licence partners for data on various fields on the Norwegian shelf.• Thanks to everybody who has inspired me!• Thanks to everone who has contributed!

×