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From loose grains to stiff rocks –
The rock-physics "life story" of a clastic
sediment, and its significance in QI studies
Prof. Per Avseth, NTNU/G&G Resources
The rock physics “life story” of a clastic sediment
– a teaser:
1Ksat
1Kmineral
+
K + K fluid
Age (M.yrs)200 0
Bu
rial
dep
th/T
emp
.
70 oC
Chemical compaction
Mechanicalcompaction
Tectonic uplift
100
A
BA
B
0.30 0.35 0.40
Ela
stic
Modulu
s
Po ro sity
ContactCement
Init ialSandPack
Friable
ConstantCement
Sorting variability
Chemical compaction
Mechanical compaction
Deposition
HC trends
Acoustic Impedance
Vp/Vs
B
A
Bjørlykke (2015)
Pore compressibilitystrongly affected by diagenesis!
3
Selected references:
• Helset et al., 2004: Combined diagenetic and rock physics modeling for improved control on seismic depth trends (EAGE Abstract)
• Brevik et al., 2011: Rock Physicist step out of the well location, meet geophysicists and geologists to add value in exploration analysis (The Leading Edge).
• Dræge et al. 2014: Linking rock physics and basin history – Filling gaps between wells in frontier basins (The Leading Edge).
• Zadeh et al. 2016: Compaction and rock properties of Mesozoic and Cenozoic mudstones and shales, northern North Sea (Marine and Petroleum Geology).
• Avseth and Lehocki, 2016: Combining burial history and rock-physics modeling to constrain AVO analysis during exploration (The Leading Edge).
Geology GeophysicsRock Physics
Bridge & Bottle-neck Few observablesMany parameters
Ambiguities
QI prediction
Limitations/ResolutionUncertainties
Pit-fallsMore/Better data!More knowledge!
More integration!
ComplexityNoise/Artifacts
Variability
Reducing uncertainties through integration
Case example from North Sea (Alvheim Field)
Sand and shale compaction trends
in the North Sea
Alvheim well (Kneler discovery)
Velocity jump in sst due to cementation
Friable sst
CCT
0.30 0.35 0.40
Ela
stic
Modulu
s
Porosity
ContactCement
InitialSandPack
Friable
ConstantCement
Vclay Vp Porosity
Oil leg
Burial history and subsidence curves for top
reservoir sst at Kneler well (schematic)
Burial depth/temperature
Time (M.yrs before present)
0-15-60
Present day burial
Upper Sst Unit
Lower Sst Unit
Time range of target > 70C (= cementation)
70C = ca. 2km
0
Maximum burial
DepositionPaleocene
Tilting/Uplift Miocene
Continuoussubsidence
AVO classification constrained by depth trends
(Alvheim field, North Sea)Rimstad et al. (2012):(Bayesian classification)
Avseth and Lehocki (2016)(Mahalanobis distance)
BrineOil
Gas
shale
Uncon.
Cemented
GasOil Brine
shaleCem.
Unc.
Are injectites on Volund cemented or not?
From Schwab et al. 2015
Well log data from 24/9-6
0 50 100 150
2000
2050
2100
2150
2200
2250
GR
De
pth
(m
)
0 2 4
Velocity
4 6 8 10 12
Acoustic impedance
1.5 2 2.5 3
Vp/Vs
Intra Balder (oil)
Intra Balder (brine)
Hermod
Heimdal
AI Vp/VsVs & VpGR
2000m
2250m
Rock Physics diagnostics of Paleocene sandstone units
0.15 0.2 0.25 0.3 0.35 0.4 0.451.5
2
2.5
3
3.5
4
4.5
Porosity
Vp
(km
/s)
Balder sst 1
Balder sst 2
Hermod
Heimdal
Unconsolidated sand model
Dvorkin-Nur
contact cement model
0.30 0.35 0.40
Ela
stic
Modulu
s
Po ro sity
ContactCement
Init ialSandPack
Friable
ConstantCement
Combined modeling of burial
history and rock physics
Mechanical compaction (Lander and Walderhaug, 1999)
Chemical compaction (Walderhaug, 1996), when T > 70 C
Rock physics modeling
0.30 0.35 0.40
Ela
stic
Modulu
s
Porosity
ContactCement
InitialSandPack
Friable
ConstantCement
Hertz-Mindlin (mech. comp)Dvorkin-Nur + Hashin-Shtrikman
(chemical compaction)
Slide 13
Stable packing configuration
Dep. porosity
Initial volume of pore filling material
Exponential decline factor
Effective stressSum of pore space:
Volume of Qz cement precipitated between time T1 and T2
Volume of Qz cement at time T1
Molar weight of qz Qz- precipitation rateQz- surface area
Qz- densityPorosity at Cement start Heat rate
Combined burial and rock physics modeling of porosity versus P-
wave velocity (sensitivity study)
Vp/VsAcoustic Imp.
PorosityCement volume
Rock physics and AVO modeling constrained
by burial history
Slide 15
1. Burial history
Burial depth (m)Temperature (degrees C)
Geologic Age (M.Yr)0250
Stø Fm
Deposition
Max. burial
(Present day burial)
2. Diagenetic modeling (Walderhaug)
Depth/Temperature
Onset cement
3. Rock physics modeling (Dvorkin-Nur)
Depth/Temperature
Oil
Brine OilBrine
4. AVO modeling (Zoeppritz)
+ shalecompaction
and RP Intercept+-
+
-
Gradient
Deposition Brine
Oil
Shale (Background)
Max. burial
A «typical» present day
geo-section offshore Norway
16
Quarternary sediments
Sea water
Miocene sediments
Oligocene-Eocene
Paleocene
Cretaceous
Syn-rift
Jurassic/Triassic
Prospect A
Prospect B Prospect C
Discovery
70 C
Cenozoic upliftIncreasing landward
«Restoring» geo-section to maximum burial.
Have prospects been into the frying pan?
17
The “Frying Pan”(T>70 C required for Qz-cem. )
Burial constrained AVO
modeling at “Discovery” well.(Campanian sands w/oil give AVO class III)
“Frying pan” (chemical compaction/Qz cementation)
Brine sst
Oil
Oil
Brine
Shale
Shale
Brinesand
Burial curve
70 C
Fluid trend
Compaction trendBrine
Oil
Burial constrained AVO modeling at prospect A
(Paleocene sst)
Oil-filled sst = AVO class I-IIp
19
“Frying pan”
Brine sstBrine sst
Oil Oil
OilBrine
Shale
Shale
Brinesand
Burial curve
70 C
Fluid trend
Compaction trend
Burial constrained AVO modeling at prospect B
(Paleocene sand)
Oil-filled sst = AVO class III
“Frying pan”
Brine
Oil
Brine
Oil
OilBrine
Shale
Shale
Brinesand
Burial curve
70 C
Fluid trend
Compaction trend
Burial constrained AVO modeling at prospect C
(Aptian sst)
Oil-filled sst = AVO class IIp
“Frying pan”
Brine sst
Oil
Brine sst
OilFluid trend
Compaction trend
OilBrine
Shale
Shale
Brinesand
Burial curve
70 C
RPT and AVO analysis
@Pingvin well 7319/12-1
22
Fluid trend
Porosity/Rock stiffness
shaleBrinesandGas
heterolithics
Limestone
AI
Vp/Vs AI Vp/Vs
Litho/Fluid classification
Intercept
Gra
die
nt
Gas
Gas(tight)
Burial analysis and simulated AVO signatures in Pingvin
(7319/12-1)
23
Net erosion mapfrom N. Johansen (2017)
Unc.sand
Cem.sst
Sorting
Diag.
Brine sand
Oil
OilBrine
Max burial = 1250m
Uplift = 700m
ShaleBrine
Oil
Reservoir
Cap-rock
700
The reservoir sands in Pingvin has not been buried deepenough to be cemented! Hence, great fluid sensitivity! AVO class III expected for any HC-fill.
Onset cementation = 70C
GasGas
Gas
Eocene more deeply buried in Sørvestnaget Basin:
Burial constrained AVO at well 7216/11-1S
24
Onset cementation = 70oC
OilBrineGas
Wisting example
Net uplift=1500m (Temp grad=42.5C/km)
Gas Oil Brine
Summary:
How burial controls AVO and fluid sensitivity
Pingvin
EoceneProspect 1
Eocene Prospect 2
Juraprospect
Age
depth
70oC
AVO class III
AVO class III-IV
AVO class II-IIp
AVO class II-III
Conclusions
• The present day seismic signatures will reflect depositional and burial
history, and this knowledge should be included in AVO and QI studies.
• Rock physics modeling can be combined with burial modeling for
uplift estimation, to constrain low-frequency trends, and to model
expected AVO signatures.
• Normally, bright seismic amplitudes and class II-III AVO signatures are
only associated with unconsolidated to poorly consolidated sandstones.
• There is likely a lot of «hidden» hydrocabrons (esp. oil) in consolidated
sandstone reservoirs with stiff rock frame and reduced fluid sensitivity,
that can be challenging to discover during AVO and QI studies.
28
Acknowledgements
• Thanks to Ivan Lehocki at Lehocki Geospace for contributions to
burial modeling codes.
• Thanks to MCG for AVO data on Pingvin
• Thanks to FORCE for the invitation
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