Fluid substitution effects on seismic anisotropy
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Transcript of Fluid substitution effects on seismic anisotropy
Fluid substitution effects on seismic anisotropy
Long Huang, Robert Stewart, Samik Sil, and Nikolay Dyaur
HoustonApril 2nd, 2014
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Outline Motivation Natural fractures and anisotropy, fluid effects
Theory and methods Anisotropic Gassmann’s equations, parameterize, recast Gassmann’s equations
Discussions P- & S-wave moduli and velocities, Thomsen’s parameters, azimuthal amplitude variation
Conclusions
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X
ZY
Orthorhombic
Beautiful fractured Atoka Sandstone at Natural Dam.
(Liner, 2013)
X
YZ
HTI (http://www.rechproject.com/related-project.html)
The deformation in carbonates rocks
How to characterize these fractured rocks?How would fluid influence their physical properties?How about seismic anisotropy with different fluids?
Fractures
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(Huang et al., 2013)
Theory
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X
YZ
2
1 22
11 1 21 2
m fl m
1 -2
2 1/ K -K K - 1
2
drym iso N N
satN N dry
dry iso N Nm fl iso
K KC r
KK K K
11 12 13
12 22 23
13 23 331 1 2 2
44
55
66
0 0 00 0 00 0 0
( , , , , , )0 0 0 0 00 0 0 0 00 0 0 0 0
ORTij N T N T
C C CC C CC C C
C fC
CC
(Schoenberg, 1980; Schoenberg and Sayers, 1995;Bukulin et al., 2000)
Dry term Fluid term (Gassmann, 1951)
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m fl m/ K -K K -Kmsat
m fl
K KK K
K K
3,2,1,,,,
/9C-KK-K/3/3/
pqmflmij
ji
KKCKCK
CCflm
jmimij
sat
Dry term Fluid term (Gassmann, 1951)
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44 21satTC
55 11satTC
1 266
1 2
1 11
T Tsat
T T
C
2
1 22
11 1 21 2
m fl m
1 -2
2 1/ K -K K - 1
2
drym iso N N
satN N dry
dry iso N Nm fl iso
K KC r
KK K K
2
1 22
22 1 21 2
m fl m
1-2
2 1/ K -K K - 1
2
drym iso N N
satN N dry
dry iso N Nm fl iso
K KC r
KK K K
2
1 22 2
33 1 21 2
m fl m
1-2 2
2 1/ K -K K - 1
2
drym iso N N
satN N dry
dry iso N Nm fl iso
K KC r r
KK K K
The complete recipe
Gas to brine substitution: S-waves
Shear-wave moduli are independent of fluid type Shear-wave velocities depend on fluid type due to density change
1 20.5, 0.1T T
44 44 21sat dryTC C
55 55 11sat dryTC C
1 266 66
1 2
1 11
T Tsat dry
T T
C C
Φ=5%
Φ=25%
Red is for gasBlue is for brine
Φ=5%
Φ=5%
Φ=25%Φ=25%
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Gas to brine substitution: P-wave
Φ=5%
Φ=25%
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Porosity (φ) Δ C11 Δ C22 Δ C33
5% 38% 5% 2%25% 56% 23% 19%Porosity (φ) Δ Vpx Δ Vpy Δ Vpz
5% 16% 1% 0%25% 19% 6% 4%
Φ=5%
Φ=25%
Red is for gasBlue is for brine
Fluid substitution effects on P-wave are anisotropic
P-wave moduli of high-porosity sands are more sensitive to fluids
Vertical P-wave velocity of low-porosity sands is constant with fluids
X
YZ
Φ=5% Φ=5%
Φ=25%Φ=25%
gas gas
gasgas
brine brine
brinebrine
Porosity (φ) Δ ε1 Δ δ1 Δ ε2 Δ δ2
5% -22% -9% -5 % -35 %25% -30% -20% -13% -31%
Gas to brine substitution: Thomsen’s parameters
Shear-wave splitting (γ) is independent on fluids Both ε and δ are sensitive to fluids
(1)2
(1)2 2
(1)2
2 1 ,
2 [ 1 2 ],N
N T
T
g g
g g
(2)1
(2)1 1
(2)1
2 1 ,
2 [ 1 2 ],N
N T
T
g g
g g
(1)
(2)
(Bakulin et al., 2000)
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Φ=5%Φ=25%
Red is for gasBlue is for brine
X
YZ
X
ZY
(1) (1) (1), ,
(2) (2) (2), ,
YZ plane XZ plane
brine
brine
gas
gas
Porosity (φ) Δ AVAZ (30°)5% 12%25% -6%
Gas to brine substitution: AVAZ
High-porosity: gas sands have more azimuthal amplitude variations Low-porosity: wet sands have more azimuthal amplitude variations
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Shale
Sandstone
X (0°)Y (90°)P-wave reflectivity
(180°)
(Rpp calculated from Václav Vavryčuk and Ivan Pšenčík, 1998)(Azimuth versus incidence angle)
Future work: experiments with 3D printed models
Shear-wave splitting in both directions implies it’s slightly orthorhombic material.
(Huang et al., 2013)
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3D printed cube with penny-shaped cracks.
Extended Gassmann’s equations for an orthorhombic medium
Shear rigidity and splitting are independent on fluid type, but not shear-wave velocity
Fluid substitution effects are anisotropic
Vertical P-wave velocity of low-porosity sands is constant with fluids
High-porosity gas sands or low-porosity wet sands, have more azimuthal amplitude variations
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Conclusions
Acknowledgement
• Allied Geophysical Laboratories, UH
• Dr. Robert Sheriff and SEG Foundation
• UH adjunct and research professors: Dr. Leon Thomsen and Dr. Colin Sayers
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Thank you!
Questions?