Download SEDIMENT COMPACTION - THE BARENTS SEA ROCK

SEDIMENT COMPACTION - THE BARENTS SEA
ROCK PROPERTIES (BARROCK) PROJECT,
Jens Jahren, N. H. Mondol & B. Thyberg
Project presentation and some results from earlier and
ongoing compaction studies at the University of Oslo
BarRock
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Barents Sea Rock Properties (BarRock)
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Objectives: To analyze rock property distributions in shales and sandstones in the
uplifted Barents Sea area.
To study Porosity, permeability, seal integrity and deformation related to primary
and secondary petroleum migration in an uplifted cemented sedimentary
sequences.
University of Oslo, Department of Geosciences
Partner - Norwegian Geotechnical Institute
Additional cooperation with Russia and USA
Financed by PETROMAKS and University of Oslo
Start 2010-06
End 2014-09 (UiO PhD)
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Associated project: ”Cementation and Rock Properties in Organic Rich Siliciclastic
Rocks” financed by ConocoPhillips
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The project aims to integrate sedimentology, diagenesis, geomechanical
properties, rock physics, structural geology and geophysical/seismic properties to
better understand the behavior of sedimentary rocks in an uplifted area and how
the fluids and fluid movement are affected during uplift.
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The challenge is to relate geology to geophysics where no satisfactory quantitative
relations exist between different sedimentary rocks and their geophysical
properties.
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Experimental compaction tests have provided a basis for understanding rock
mechanical properties of different sediments.
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Studies of cemented rocks show that quartz cementation dominate porosity loss
below a depth corresponding to about 70 oC. Cementation processes continue also
during uplift if the temperature is higher than about 70 oC.
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Quantification of these potentially important stress relaxing cementation
processes during uplift has not been addressed in detail before. Stress relaxation
from cementation would reduce brittle deformation due to stress redistribution
related to uplift processes proposed for the Barents Sea Area (e.g Makurat et
al.1992).
Work Packages (WP’s)
• WP1: Sedimentology, fluid migration, compaction and cementation (PI: Jens
Jahren)
• WP2: Rock mechanical testing, rock physics and seismic modeling and
quantitative seismic interpretation (PI: Nazmul Haque Mondol)
• WP3: Structural geology in relation to rock properties – case study (PI: Roy
Helge Gabrielsen)
• WP4: Regional uplift and erosion in relation to rock properties (PI: Jan Inge
Faleide)
• WP5: Integration and synthesis – Barents Sea Petroleum system (all PI’s)
• PhD students (WP1 – financed by UiO, WP2 – financed by PETROMAKS)
Compaction of sediments (and rock stiffening) in subsiding
basins involves both mechanical and chemical processes
• During early burial siliceous
sediments compact mostly
mechanically (2-3 km/60-80 ◦C).
Mechanical compaction is
governed by increasing
effective stress resulting in
volume reduction due to
rearrangements or breaking of
grains.
• Chemical compaction is a
function of thermodynamics
and kinetics and are rather
insensitive to the effective
stress.
Mechanical
compaction
(effective stress)
Bjørlykke, 1998
Diagenetic processes during burial
Time
10
Uplift
Extension
Brittle deformation
40
Mechanical
compaction
70
Chemical compaction
(quartz cementation
110
Temperature
140
Integrated Time
Temperature
Illitization of kaolinite
and K-feldspar
Porosity
Chemical compaction continues also during
uplift at temperatures higher than about 60◦C
Continued
chemical
compaction
during
uplift
Bjørlykke 2010
Velocity-depth trends in the Barents
Sea area is clearly affected by
Chemical processes during uplift
Sonic velocity
measurements
with depth) from
the Haltenbanken
area
Sonic velocity
measurements
the Barents
Sea area
Storvoll (2005)
Experimental mechanical compaction
Time (Hours)
600
Time needed to maintain
drained condition for
different clay aggregates
400
200
0
0
10
20
30
40
50
Smectite (100%)
Smectite (80%), Kaolinite
Smectite (60%), Kaolinite
Smectite (40%), Kaolinite
Smectite (20%), Kaolinite
Kaolinite (100%)
(20%)
(40%)
(60%)
(80%)
Vertical Effective Stress (MPa)
Mondol et al. 2008a,b
Compression
Porosity (%)
0
20
40
60
80
Vertical Effective Stress (MPa)
0
Kalonite: 20%
Smectite: 42%
10
20


30
40
Kaolinite (100%)
Smectite (20%), Kaolinite
Smectite (40%), Kaolinite
Smectite (60%), Kaolinite
Smectite (80%), Kaolinite
Smectite (100%)
(80%)
(60%)
(40%)
(20%)
50
Mondol et al. 2008a,b
2500
Velocity-porosity relationship
Velocity (m/ s)
2000
Kaolinite (100%)
Smectite (20%), Kaolinite
Smectite (40%), Kaolinite
Smectite (60%), Kaolinite
Smectite (80%), Kaolinite
Smectite (100%)
1500
1000
(80%)
(60%)
(40%)
(20%)
500
10
20
30
40
50
Stress-velocity relationships
60
Porosity (%)
1000
2200
800
Vs (m/ s)
Vp (m/ s)
2000
1800
600
1600
400
1400
200
0
20
40
Vertical Effective Stress (MPa)
0
10
20
30
40
50
Vertical Effective Stress (MPa)
Mondol et al. 2008a,b
Mondol et al 2008a
Mondol et al. 2008a
Rock stiffening
Mondol et al. 2008b
Mechanical and chemical compaction in
Sandstones -Etive Formation, North Sea
Lab experiments on loose Etive sand representing mechanical
compaction only. Deviation from mechanical compaction trend
represent chemical compaction (quartz cementation).
Marcussen et al 2009
How quartz cementation
in sandstones works
Intra granular volume (IGV) is not much affected by quartz
cementation indicating that dissolution at stylolites is the main
contributer of silica (passive innfilling between grains.
Marcussen et al 2009
Chemical compaction in mudstones
• Quartz cementation and clay mineral transformations - The simplified
reaction equations below illustrate the two most important clay
mineral reactions:
– Smectite + K+ = Illite + Silica + H20 (e.g., Boles and Franks, 1979).
• taking place between about 60-100 ºC
– Kaolinite + K+ = Illite + Silica + H20 (e.g., Bjørlykke et al.,1995)
• taking place at temperatures greater than 120-140 ºC
– The reactions requires a potassium source (K-feldspar) and silica removal
(precipitation or transport out of the system) to proceed (e.g., Bjørlykke
and Aagaard, 1992).
How smectite affect compaction
(measured as velocity - all samples buried to similar depth/temperature)
Marcussen et al. 2009
Mudstone velocity depth trends – North Sea
Hordaland group – smectite rich
Marcussen et al. 2009a
Smectite even affect reflectivity – red curve represent bulk smectite
Marcussen et al. 2009a
Mudstones - Norwegian Sea
Depth (msf)
How clay mineralogy affect both mechanical and chemical compaction
0
0
0
1000
1000
1000
2000
2000
2000
3000
3000
3000
4000
4000
4000
5000
5000
5000
0
0.2
0.4
PHI
0.6
0.8
1000 1500 2000 2500 3000 3500
Vp
1.6
2
2.4
2.8
RHOB
Peltonen et al., 2009
0-1000 m – Mechanical compaction of glacial clays
1000-2000 m - Mechanical compaction of smectite rich clays
2000- 3500 m – Chemical compaction (quartz cementation and illite formation
Blue compaction curve – Experimental compaction of 75% kaolinite-25% silt sample
Quartz cementation in mudstones
Petrographic evidences of microquartz crystals
Micro-quartz crystals embedded in the
fine-grained clay matrix
Well 33/5-2, 2370 m/75◦C
CL-response from microquartz indicate an
authigenic quartz origin
CL-response
of the detrital
grain is
taken from
Peltonen et
al. (2009)
EDS spectrum of the illitized clay
matrix chemistry (un-filled) and the
micro-quartz crystals (filled)
Thyberg et al. 2009).
Micro-quartz cement embedded in the
fine-grained clay matrix
Well 33/5-2, 2570 m/80◦C (right)
Below approx 2500 m/80-85◦C: inter-grown
aggregates of micro-quartz and clay
crystals typically dominate (bottom left)
Continuous quartz cement growth. Well
6505/10-1, 2620m/90-95◦C (bottom right)
Quartz cement platelets representing formation of incipient
schistosity (quartz outlined in green)- Well 6505/10-1, 4300 m/150◦C
Thyberg and Jahren 2010