1 Guangsheng Gu 1 Advisors: George J. Hirasaki 1, Walter G. Chapman 1 Collaborators: Colin A. Zelt...
25
1 Guangsheng Gu 1 Advisors: George J. Hirasaki 1 , Walter G. Chapman 1 Collaborators: Colin A. Zelt 2 , Priyank Jaiswal 2 1 Dept. of Chemical & Biomolecular Engineering 2 Dept. of Earth Science Rice University, Houston, TX, 77005 Consortium on Processes in Porous Media, 15th, April 26, 2011 Rice University, Houston Seismic Characteristics in Marine Hydrate Systems
-
Upload
theresa-lincoln -
Category
Documents
-
view
214 -
download
0
Transcript of 1 Guangsheng Gu 1 Advisors: George J. Hirasaki 1, Walter G. Chapman 1 Collaborators: Colin A. Zelt...
1
Guangsheng Gu1
Advisors: George J. Hirasaki1, Walter G. Chapman1
Collaborators: Colin A. Zelt2, Priyank Jaiswal2
1 Dept. of Chemical & Biomolecular Engineering2 Dept. of Earth Science
Rice University, Houston, TX, 77005
Consortium on Processes in Porous Media, 15th, April 26, 2011 Rice University, Houston
Seismic Characteristics in Marine Hydrate Systems
2
• Stable at high pressure and low temperature, typically in deep marine sediments or in permafrost environments
What is Gas Hydrate
• Crystalline compounds, with gas molecules (e.g. CH4, C2H6) captured in water molecular cages
• Dissociation:
1m3 methane hydrate = 168 m3 CH4 + 0.8 m3 H2O
3
Why Study Hydrates?
World-wide distribution; huge potential amount, as energy resource
Geohazards -Submarine slope failure
Influence on global climate change
T.S. Collett, Offshore Technol. Conf. (OTC) 2008.
4
Major Seismic Characteristics
• Used to identify hydrates in marine sediments
• Bottom Simulating Reflector (BSR)
• Seismic Blanking in Lateral Strata
• Wipeout in Gas Chimeny
5
Bottom Simulating Reflector (BSR)
A strong reflector below seafloor Parallel to the seafloor Indicating the abrupt transition from hydrate to free gas phase below In good accordance with 3-phase equilibrium of a pure-methane
system
Taylor et al., 1992; M.W. Lee et al, 2001
Hydrate or Gas Saturation
Abrupt Change
6
Seismic Blanking in Lateral Strata
• Hydrate accumulation induces blanking
7
Seismic Blanking
MJ. Hornbach, WS. Holbrook, et al., Geophysics, v. 68, n. 1, 92–100,2003.
8
Seismic Blanking
• Weak reflection in seismic profiling:
R < RBSR/10
Typically R < 0.02
9
Geologic Setting
1 ,1 ,1 ,1 1 ,1 1, , , , , ,H W V pS S S V Z
Layer 1
Layer 2 (shale/clay) 2 ,2 ,2 ,2 2 ,2 2, , , , , ,H W V pS S S V Z
In Reflection
12
12
ZZ
ZZR
Reflection Coefficient:
12
22
ZZ
ZT
Transmission Coefficient:
1010
Estimation of Acoustic Properties
Revised from the Time-average Equation (Pearson et al., 1983).
Average P-wave Velocity:
Average Density:
phase i =w,H,V
1111
Intrinsic Properties of Phases
Component Vp (m/s) (kg/m3)
Sea Water (w) 1500 1030
Hydrate (H) 3300 900
Mineral1 (sand) 200 ~ 2000 2500
Mineral2 (diatomite) 2000 2000
Reference Mineral (shale/clay) 2000 ~ 2400 2600
Parameter Value
Porosity1 (in sand layer) 0.2 ~ 0.3
Porosity2 (in shale layer) 0.2~0.7
Sh 0~1
Table 1: Acoustic properties of components
Table 2: Porosity and saturation ranges
Acoustic velocities from W.J. Winters and W.F. Waite (2007); Sloan (2007), etc..Nick Barton, Rock Quality, Seismic Velocity, Attenuation and anisotropy, Taylor & % Francis Group, 2007, p. 12.
The ranges of porosity were obtained from Hirasaki (lecture note, 2006), Jenyon (2006), Magara (1980).
12
(Case 1) Impossible to be blanking
BlankingRange
0 0.2 0.4 0.6 0.8 12.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
3.3
3.4x 10
6
Sh, %
Ave
rage
Im
pe
dan
ce,
kg/(
m2 *s)
Average Impedance in Sand Layer
sand
= 0.3 shale
= 0.5
Vpsand
= 1000 Vpshale
= 2400
Sand Layer
Shale Layer
13
(Case 2) Possible to be blanking
BlankingRange
0 0.2 0.4 0.6 0.8 13.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9x 10
6
Sh, %
Ave
rage
Im
pe
dan
ce,
kg/(
m2 *s)
Average Impedance in Sand Layer
sand = 0.3
shale = 0.5
Vpsand = 1500 Vpshale = 2400
Sand Layer
Shale Layer
14
(Case 3 ) Impossible to be blanking
BlankingRange
0 0.2 0.4 0.6 0.8 13.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
5x 10
6
Sh, %
Ave
rage
Im
pe
dan
ce,
kg/(
m2 *s)
Average Impedance in Sand Layer
sand
= 0.3 shale
= 0.5
Vpsand
= 2000 Vpshale
= 2400
Sand Layer
Shale Layer
15
Reflection Coeffiecient
Layer porosity Vp (m/s) Density (kg/m3)Layer 1 (quartz) 0.3 1000 2650
Layer 2 (Clay/Shale) 0.4~0.7 2400 2600
Blanking region
-0.26
-0.26-0.24
-0.24
-0.24-0.22
-0.22
-0.22-0.2
-0.2
-0.2-0.18
-0.18
-0.18-0.16
-0.16
-0.16-0.14
-0.14
-0.14-0.12
-0.12
-0.12-0.1
-0.1
-0.1-0.08
-0.08
-0.08-0.06
-0.06
-0.06-0.04
-0.04
-0.04
-0.02
-0.02
-0.02
0
0 0.02
Sh
o
f cl
ay
Reflection Coefficient from A certain layer to Clay Layer
0 0.2 0.4 0.6 0.8 10.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
-0.25
-0.2
-0.15
-0.1
-0.05
0
Just possible to be
blanking
Sh in sand layer
16
Reflection Coeffiecient
Layer porosity Vp (m/s) Density (kg/m3)Layer 1 (quartz) 0.3 1500 2650
Layer 2 (Clay/Shale) 0.4~0.7 2400 2600
Very possible to be blanking
-0.12 -0.1
-0.1
-0.08
-0.08
-0.08
-0.06
-0.06
-0.06
-0.04
-0.04
-0.04
-0.02
-0.02
-0.02
0
0
0
0
0.02
0.02
0.02
0.04
0.04
0.04
0.06
0.06
0.06
0.08
0.08
0.08
0.1
0.1
0.1
0.12
0.12
0.12
0.14
0.14
0.14
0.16
0.16 0.18
Sh
o
f cl
ay
Reflection Coefficient from A certain layer to Clay Layer
0 0.2 0.4 0.6 0.8 10.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
-0.1
-0.05
0
0.05
0.1
0.15
Blanking region
17
Reflection Coeffiecient
Layer porosity Vp (m/s) Density (kg/m3)Layer 1 (quartz) 0.3 2000 2650
Layer 2 (Clay/Shale) 0.4~0.7 2400 2600
Just Possible to be blanking
-0.02 0
00.02
0.02
0.04
0.04
0.04
0.06
0.06
0.06
0.08
0.08
0.08
0.1
0.1
0.1
0.1
0.12
0.12
0.12
0.14
0.14
0.14
0.16
0.16
0.16
0.18
0.18
0.18
0.2
0.2
0.2
0.2
0.22
0.22
0.22
0.24
0.24
0.24
0.26
0.26 0.280.3
Sh
o
f cl
ay
Reflection Coefficient from A certain layer to Clay Layer
0 0.2 0.4 0.6 0.8 10.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0
0.05
0.1
0.15
0.2
0.25
Blanking region
18
Different Layer (Diatomite vs. Clay)
Layer porosity Vp (m/s) Density (kg/m3)Layer 1 (Diatomite) 0.65 2000 2000Layer 2 (Clay/Shale) 0.4~0.7 2400 2600
-0.22
-0.2
-0.18
-0.18
-0.16
-0.16
-0.14
-0.14
-0.14
-0.12
-0.12
-0.12
-0.1
-0.1
-0.1
-0.08-0.08
-0.08
-0.08
-0.06
-0.06
-0.06
-0.06
-0.04-0.04
-0.04
-0.04
-0.02
-0.02
-0.02
0
0
0
0.02
0.02
0.02
0.04
0.04
0.06
0.06
0.08
0.08 0.10.12
0.14
Sh
o
f cl
ay
Reflection Coefficient from Diatomite to Clay Layers
0 0.2 0.4 0.6 0.8 10.4
0.45
0.5
0.55
0.6
0.65
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
Blanking region
Very possible to be blanking
19
Conclusion
Hydrate accumulation in marine sediment is helpful for blanking; Sensitive to parameters and stratum lithology;Hydrate accumulation doesn’t guarantee a blanking.
20S. Horozal et al., Marine Geology 258: 126–138, 2009.
KIGAM data showing BSR in debris-flow deposits (DFD). BSR is weak and discontinuous. Seismic chimneys look very narrow due to vertical exaggeration (ca. 14×). Seismic chimney, marked by S, is about 820 m wide and 110 m tall above the BSR, forming a rather horizontal zone of amplitude reduction. DFD, debris-flow deposits; THS, turbidite/hemipelagic sediments.
Wipeout in gas chimneyWipe outin vertical columnar regions
21
gas chimney
Geological Society of America Bulletin, Riedel, 2006.
Northern Cascadia margin near Ocean Drilling Program (ODP) Site 889/890.
22Riedel, 2006.
23
chimney
S. Horozal et al., Marine Geology 258: 126–138, 2009.
24
Mechanisms
• Due to gas bubbles in the GHSZ in the Cascadia Margin (Wood et al., 2002). These gas bubbles may be coated with hydrate that prevents the inflow of water (Riedel et al., 2006).
• Due to a thermal (Wood et al., 2002) or a thermo-chemical effects (Hornbach et al., 2005)
• Due to presence of gas hydrate, and intrinsic acoustic properties in sediments (Chand and Minshull, 2003.).
25
Acknowledgement• DOE Grant (No. DE-FC26-06NT42960)• Rice University, Hirasaki Group, Chapman Group• Colleagues in Earth Science Department
