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$Drilling-induced tensile wall-fractures - Stanford University$

Eichhubl et al., 2004) did not lend significant cohesion to the detrital grains (Sternlof et al., 2005) or, at least that it did not impede CB formation. Why the lower boundary of the alteration front is located stratigraphically where it is, and why this horizon roughly coincides with the lower extent of compaction band formation remains a significant open question. Given that the bands predate alteration and pure coincidence is unlikely, it is interesting to speculate, however, that the relatively newly formed CB arrays in the Cretaceous Aztec sandstone played an active role in attracting and concentrating flow of the expulsing brines. As described above in Section 3, a preponderance of evidence indicates that the Aztec sandstone in the immediate study area just avoided being overridden by the Willow Tank and Muddy Mountain thrust sheets and that, based on diagenetic evidence, has never been buried by much more than the combined thickness of overlying Cretaceous and Neogene sediments (~1,600 m). Directly overlying the Aztec is the basal conglomerate of the Willow Tank formation, interpreted to be a gravel pediment indicative of erosional/depositional stasis. An upward coarsening, 1,300-m-thick sequence of Cretaceous deposition followed (Figure 1.2), dominated by more than 1,100 m of the Baseline sandstone representing aqueous redeposition of the Aztec from western upland sources into a foreland basin (Longwell, 1949; Bohannon, 1983). Up to 600 m of these lower Cretaceous sediments are overridden by the Willow Tank thrust, which is associated with shear banding in the Aztec that post-dates CB formation. Sternlof et al. (2005) conclude that no more than 600 m of fine-grained foreland basin sediments buried the Aztec sandstone during CB formation, and likely less. We further suggest that the evolution of this flexural foreland basin was in its earliest stages during CB formation and that no more than 200 m of clay-rich swampland deposits of the Willow Tank formation covered the Aztec. The end-member scenario is that the Aztec sandstone was essentially unburied, covered only by the gravel pediment, which is suggestive of mild uplift related to broad regional warping of the crust at the onset of the Sevier compression (Fleck, 1970; Brock and Engelder, 1977). In any case, it appears certain that CB formation in the Aztec occurred well before the thrust front reached the area. This interpretation is further corroborated by the observation that CBs exposed at Buffington Pockets (Figure 1.3) are substantially similar in geology and orientation to 30
those at the Valley of Fire, despite having been overridden by up to 5 km of the Muddy Mountain thrust sheet (Brock and Engelder, 1977) and probably rotated in a clockwise sense during later movement along the Las Vegas Valley shear zone and Lake Mead fault system (Figure 1.3). To summarize, we interpret CBs to have formed in the Aztec sandstone when it was shallowly buried (< 600 m) and well before active east-vergent thrust faulting affected the area. There is no evidence to suggest that the Aztec at this time was anything more than a weakly cemented granular aggregate (albeit one with a complex depositional architecture) topped with relatively thin (
Page 1 and 2: STRUCTURAL GEOLOGY, PROPAGATION MEC
Page 4 and 5: Abstract Low-porosity, low-permeabi
Page 6 and 7: delivered with fortitude, humor, su
Page 8 and 9: Chapter 3—Energy-release model of
Page 10 and 11: List of Illustrations Figure A. Cov
Page 12 and 13: Figure A. Cover photo that accompan
Page 14 and 15: likely present in subsurface sandst
Page 16 and 17: hooking-tip interactions—using th
Page 18 and 19: and sandstone, my co-authors—Moha
Page 20 and 21: the hard data from which accurate p
Page 22 and 23: Although the Aztec sandstone experi
Page 24 and 25: Waterpocket Fault 36 o 26‘ N 0 1
Page 26 and 27: Cenozoic Mesozoic Paleozoic Quatern
Page 28 and 29: 3.3. Deformation The Aztec also has
Page 30 and 31: There also are relatively high-angl
Page 32 and 33: (e) (f) (c) 500µm compaction band
Page 34 and 35: dihedral angle of 80° or more, and
Page 36 and 37: 5. Compaction band orientations Ori
Page 38 and 39: n = 20 M n = 20 P n = 22 B n = 20 R
Page 40 and 41: were encountered, giving the dihedr
Page 44 and 45: P (a) (c) S P S Figure 1.10. Stereo
Page 46 and 47: possible, and use these to better c
Page 48 and 49: 1.5(ρgz) (b) WEST Willow Tank Uppe
Page 50 and 51: 9. Acknowledgements My sincere than
Page 52 and 53: The term compaction band (CB) was c
Page 54 and 55: Pollard, 2002). The particular util
Page 56 and 57: Hue-based image analysis using MATL
Page 58 and 59: a direct genetic relationship (Hill
Page 60 and 61: Compaction band fin Depositional be
Page 62 and 63: suggests—that to first approximat
Page 64 and 65: Porosity Porosity 0.3 0.25 0.2 0.15
Page 66 and 67: pore-clogging clay—due presumably
Page 68 and 69: 500 µm Figure 2.9. Electron backsc
Page 70 and 71: (a) (b) σ 3 σ 1 x 3 x 1 x 1 (c) u
Page 72 and 73: 6. Elastic properties Despite a lon
Page 74 and 75: Comparison of the two approaches es
Page 76 and 77: term in (6a) and (6c) begins to dom
Page 78 and 79: MPa MPa 80 70 60 50 40 30 20 10 0 0
Page 80 and 81: 2002) and use a BEM approach (Crouc
Page 82 and 83: MPa 10 4 10 3 10 2 10 1 10 −5 10
Page 84 and 85: concentration of quartz plasticity
Page 86 and 87: conducted on well-cemented sandston
Page 88 and 89: ~ 62 m compaction band trend 500µm
Page 90 and 91: Sternlof et al. (2005) have suggest
Page 92 and 93:
2005). It consists of a long (infin
Page 94 and 95:
⎡ ∆ ⎤ ⎧ p 1 ∆ ⎛ M ⎞
Page 96 and 97:
which point the inelastic strain ha
Page 98 and 99:
they can exert significant effects
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interact is inversely proportional
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(a) (b) (c) (d) Figure 4.3. Typical
Page 104 and 105:
Viewed individually, CB traces tend
Page 106 and 107:
(a) (b) (c) (d) (e) (f) Figure 4.7.
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1973; Mardon, 1988; Peck et al., 19
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undamaged host rock. That CBs canno
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0.5 0.4 0.3 0.2 0.1 0.5 0.4 0.3 0.2
Page 114 and 115:
Normalized stress magnitude 3 2.5 2
Page 116 and 117:
helps to explain why the oblique ap
Page 118 and 119:
and ts = G·ds + H·dn (2) where tn
Page 120 and 121:
plastic compaction, as suggested by
Page 122 and 123:
To determine the sensitivity of pro
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segments will self-correct to provi
Page 126 and 127:
6.3. Approaching tip interactions A
Page 128 and 129:
0.2 0.15 0.1 0.05 0 −0.05 −0.1
Page 130 and 131:
0.2 0.15 0.1 0.05 0 −0.05 −0.1
Page 132 and 133:
the hooking patterns commonly obser
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(a) (b) (c) σ1 compaction band max
Page 136 and 137:
σ 3 σ 2 σ 1 Figure 4.24. Schemat
Page 138 and 139:
NV UT CA AZ Park Road Map Detail Pa
Page 140 and 141:
compaction band Figure 5.2. Typical
Page 142 and 143:
3. Computational method The methodo
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compaction band A 5 mm A‘ compact
Page 146 and 147:
4. Application to the Aztec sandsto
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Permeability (mD) 10 4 10 3 10 2 10
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B‘ A‘ A c f m c m c f c f c f c
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equivalent of the Aztec sandstone,
Page 154 and 155:
effective permeability represents a
Page 156 and 157:
NV UT CA AZ Park Road Map Detail Pa
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Commonly from ~1 mm to ~1.5 cm in t
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Although systematic arrays of DBs p
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to 2 m, with both sets in a cross-h
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y identical blocks all subject to t
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contiguous areas. This type of char
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(0,b) n 3 (0,0) f 2 n 2 n 1 (a,0) (
Page 170 and 171:
6.1. Parallel Effective permeabilit
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By contrast, band-parallel effectiv
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Relative Effective Permeability 1.0
Page 176 and 177:
(a) (b) (c) 0 meters 3 = 10-2 kb /k
Page 178 and 179:
Though grossly systematic, anastomo
Page 180 and 181:
168
Page 182 and 183:
100 meters 5 meters NV UT CA AZ Par
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compaction band trend 500µm Figure
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Cover Outcrop Band N 100 meters 20
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(CBs) and the matrix rock in all si
Page 190 and 191:
The finite volume discretization fo
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isotropic) can lead to numerical di
Page 194 and 195:
5. Simulations Three sets of 2-D si
Page 196 and 197:
Normalized ∆P ∆P ratio (n/p) 4.
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P P P P I I P P Case 1 P P Case 2 I
Page 200 and 201:
Case 1 Case 1 Case 1 (a) (b) (c) In
Page 202 and 203:
5.2.2. Discussion The elliptical pa
Page 204 and 205:
5.3.1. Results With the regional gr
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(a) (b) Leak 200 meters Regional gr
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anticipated sustainable pumping rat
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Finally, there is the issue of fore
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200
Page 214 and 215:
Bakke, S., and Øren, P. E., 1997,
Page 216 and 217:
Carpenter, D. G., and Carpenter, J.
Page 218 and 219:
Eichhubl, P., Taylor, W. L., Pollar
Page 220 and 221:
Karimi-Fard, M., Durlofsky, L. J.,
Page 222 and 223:
-, 1987, Fracture from a straight c
Page 224 and 225:
Shipton, Z. K., and Cowie, P. A., 2
Page 226:
Wong, T. F., David, C., and Zhu, W.
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