The Influence of Listric Faults on Formation of Fractures in the Coso Geothermal Field - PowerPoint PPT Presentation

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The Influence of Listric Faults on Formation of Fractures in the Coso Geothermal Field

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F.C. Monastero, J.R. Unruh, and K. Richards-Dinger. Coso dextral releasing stepover creates a transtensional strain environment ... – PowerPoint PPT presentation

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Title: The Influence of Listric Faults on Formation of Fractures in the Coso Geothermal Field


1
The Influence of Listric Faults on Formation of
Fractures in the Coso Geothermal Field
  • F.C. Monastero, J.R. Unruh, and K. Richards-Dinger

2
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3
Coso dextral releasing stepover creates a
transtensional strain environment
4
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5
Coso Geothermal Area
A
A
0
4
Depth (km)
8
350C
350C
12
40
30
20
10
0
6
P-T Parameters for Selected Coso and Other Wells
Well TD P(max) T(max) T(grad)
P(hydro) P(litho) depth (m) bars ?C
?C/km bars bars (m)_at_400?C
A. 2,713 172 305 106 285 650 3,744 B. 2,594 217
334 120 273 622 3,333 C. 3,968 242 336 85 417 951
4,706 D. 2,967 192 341 109 312 711 3,670 E. 3,0
48 172 350 115 321 731 3,478 Kakkonda WD-1A
3,729 N.R. 515 133 392 894 3,400 San
Pompeo 2 2,930 240 gt400 125 308 703 lt2,930
Average ambient air temperature 17.8?C
7
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8
Stress Refraction in the Vertical Plane
(after Bradshaw Zoback, 1988)
9
Effective Viscosity (?eff)
?eff Ct1-n exp(E/RT)
Adapted from G. Ranalli, 1995, Rheology of the
Earth
10
Effective Viscosities of Wet Granite at Varying
Temperatures
11
The Effect of Effective Viscosity (
) Contrast on Rotation of Stress
?s
?sh
(From Bradshaw Zoback, 1988)
12
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13
Seismic P T Axes as Kamb Plots for 45 dip
normal faults
14
Seismic PT Axes as Kamb plots for flat or
vertical faults
15
Kamb contour plots of seismic P T axes for 921
Coso events on the East Flank 1-2km, 2-3 km, and
3-4 km depth intervals
16
Rotation of stress axes and effect on orientation
of Riedel shears with depth
17
Conclusions
  • Systematic changes of strain axes with depth in
    Coso field are the result of changes in effective
    viscosity with depth due to temperature
    differences
  • Orientation of related shears also change with
    depth which requires consideration of the effects
    on production and injection strategies
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