6. sedimentary micro structure
TRANSCRIPT
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Rock Physics Properties and
Sedimentary Microstructure-2Hilfan Khairy
UTP
Texture, and lithology: Rock physics basis
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
Theory and Model
`
The information of rock microstructure can be extracted from the relation ofvelocity-porosity.
Avseth, 2003
Rock physics properties change with the depositional environmentand burial depth
Adjusting an effective-medium theoretical model
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
A. Clean sandstones
1. Unconsolidated sand (friable model)
Model developed for this following contacttheory model of Hertz-Mindlin. The criticalporosity is relatively high about 0.4 and
very well sorted packing. The poorly sortedsand is accomplished by adding smallergrain deposited in the pore space. Thisadditional grain induced deterioratesorting thus decrease the porosity andslightly increase the velocity.
Avseth, 2007
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
1/322 2
22
1
18 1
c
HM
nK P
1/322 2
22
3 15 4
5 2 2 1
c
HM
nP
3 2
2 3K
K
0
z
b flP g dz
220 34 14n
Bulk modulus at critical porosity (c)
Shear modulus at critical porosity (c)
Poissons ratio
Pressure at certain depth
Coordination number
Kand are solid bulk and shear modulus respectively
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
1
/ 1 / 4
4 / 3 4 / 3 3
c cdry HM
HM HM HM
K
K K
1
/ 1 /c cdry
HM
zz z
9 8
6 2
HM HM HM
HM HM
Kz
K
Bulk and Shear modulusof friable sand
How to establish thesaturation model??
FLUID SUBSTITUTION BY USING GASSMANNS EQUATIONS
min1b fl
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
2. Contact cement model
During burial, the sand becomecemented sandstone. The effect of cement provides the rock become stifferand rigid, due to the grains are mergedtogether.
1 / 6dry c c nK n M S
3 3 1
5 20
dry c c
dry
K n S
(Dvorkin and Nur., 1996)
Saturation model? Gassmanns equations
Morecement
Avseth, 2007
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
3. Constant cement model
Constant cement model assumes that theporosity reduction come from noncontactpore-filling material, such asdeteriorating sorting. This model is a
combination of contact-cement andfriable sand model. At the beginning theporosity of sand-pack reduce to contact-cement porosity (b), and its continuesgoing down following the friable sandmodel. The friable sand model associates
with the sorting trend while the contactcement due toburial.
b
c
Avseth, 2007
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
1
/ 1 / 4
4 / 3 4 / 3 3
b b
dry b
b b b bK K K
/ 1 /b bdry
b bz z
9 8
6 2
b b b
b b
KzK
1 / 6b c c nK n M S
3 135 20
c cbb
n SK
Kb and b following thecontact cement :
The effect of fluid ?? Gassmanns equations
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
Avseth and Jrstad (2008)
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Rock physics and AVO-Universiti Teknologi PETRONAS
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B. Shales
B1. Constant-clay model for sandy shales
Silts are commonly suspended in the clay matrix and not cemented. Thus, it isfeasible to use Friable-sand model to calculate bulk modulus of constant clay.
The critical porosity for model should be very high for shales about 60%-70%.
Calculate Kmixed and mixed (quartz-clay)
Input into Friable sand model to get Kdryand dry
Performing Gassmanns fluid substitution for saturationmodeling scenario
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
1 1
mixed qz clay
C C
K K K
1 1
mixed qz clay
C C
Elastic moduli of clay minerals
1/322 2
22
1
18 1
c
HMclay
nK P
1/322 2
22
3 15 4
5 2 2 1
c
HMclay
n
P
3 2
2 3
mixed mixed
mixed mixed
K
K
0
z
b flP g dz
220 34 14n
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
1
_
/ 1 / 4
4 / 3 4 / 3 3
c cdry ssh HM
HM HM HM
K
K K
1
_
/ 1 /c cdry ssh
HM
zz z
9 8
6 2
HM HM HM
HM HM
Kz
K
Bulk and Shear modulusSandy Shale
How to establish thesaturation model??
FLUID SUBSTITUTION BY USING GASSMANNS EQUATIONS
min1b fl
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
B2. Dvorkin-Gutierrez silty shale model
shC
1
1 4
4 / 3 4 / 3 3
sat sh
sh sh q sh
C CK
K K
1
1sat sh
sh sh sh sh
C Cz
z z
9 8
6 2
sh sh shsh
sh sh
Kz
K
Porosity of shale as a function of clay content
Ksh and sh are saturatedelastic moduli of shale andthey are derived from well-log measurement of Vp, Vsand density in a pure shalezone.
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Rock physics and AVO-Universiti Teknologi PETRONAS
Dr. Hilfan Khairy
C. Shaly sandstones
C1. Constant-clay model for shaly sand
Since this model has the assumption of clay mineral dispersed in the grainand fill the pores between grains, thus it can be modeled the prediction ofelastic modulus by using Friable-sand model. The process has a similartechnique with the constant-clay model for sandy shale. However, the critical
porosity should be adjusted in between 10% to 40%, depending on the claycontent. Mineral modulus of mixed between quartz grain and shale can beestimated by applying lower bound ofHashin-Shtrikman or average of
Voigt-Reuss model. Special note should be addressed if the claycomposition is very soft such as smectite and illite (please refer to the elasticmoduli of clay minerals) and mixed with relatively stiff quartz.
Because the quartz grain are cemented and stiffer than the shale (smectiteand illite), the mixed of those two mineral should be stiffest possiblealternative. Thus, it is recommended to useVoigt bounds.
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
Calculate Kmixed and mixed (quartz-clay)
Input into Friable sand model to get Kdryand dry
Performing Gassmanns fluid substitution for saturationmodeling scenario
1
mixed q clayK C K CK
1
mixed q clayC C
1/322 2
22
1
18 1
c
HMclay
nK P
1/322 2
22
3 15 4
5 2 2 1
c
HMclay
nP
3 2
2 3
mixed mixed
mixed mixed
K
K
0
z
b flP g dz
220 34 14n
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
1
_
/ 1 / 4
4 / 3 4 / 3 3
c cdry ss HM
HM HM HM
K
K K
1
_
/ 1 /c cdry ss
HM
zz z
9 8
6 2
HM HM HM
HM HM
Kz
K
Bulk and Shear modulusSandy Shale
How to establish thesaturation model??
FLUID SUBSTITUTION BY USING GASSMANNS EQUATIONS
min1b fl
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
C2. Yin-Marion shaly sand model
The model is dedicated to predict the elastic modulus with the increasing ofclay content. By assuming the total porosity will decrease with the increasingof clay content (C) , and again it increases after threshold point, the totalporosity can be formulated as follows:
1 for C
s sh s
s sh s
sh s
C
Shaly sand
Sandy shale
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
Marion et.al., 1992
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
dry pf sat
q sat q dry s q pf
K KK
K K K K K K
1 1
pf clay fluidK K K
sat dry
1 1 1s q sh clay s sh flC C
Kdry= dry sand frame bulk modulus
dry= dry sand frame shear modulusKq = quartz bulk modulusKpf= bulk modulus pore filling material (fluid and clay)
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
Marion et.al., 1992
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
Avseth, 2007
Clean sand line
Shale line
Unconsolidated sand
Shaly sand
Silty sand
Clean sand line:constant-cement model
Shale line:constant clay model
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
Chi and Han., 2009
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
Chi and Han., 2009
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Rock physics and AVO-Universiti Teknologi PETRONASDr. Hilfan Khairy
Avseth and Jrstad (2008)
Quantifying cement from Vs-porosity graph
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Rock physics and AVO-Universiti Teknologi PETRONASD Hilf Kh i
Avseth and Jrstad (2008)
Quantifying sorting from Vs-porosity graph