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

were encountered, giving the dihedral angles between the mean orientations for each set—labeled P (primary), S (secondary) and T (tertiary), based on relative abundance. P and S share a dihedral angle of about 80° at all five locations, as do S and T at the two locations where they coexist. P and T, however share a variably low dihedral angle at these same two locations, having similar trends, but opposite dip directions. Figure 1.9 displays the combined data for all locations (n = 484) as poles, density contours, and Rose diagrams of both strike and dip orientations. Table 1.1 provides a brief statistical summary of the numbers, including mean and median dihedral angles, and relative abundance. Two basic conclusions are immediately apparent. Firstly, wherever it occurs, the secondary CB set forms essentially orthogonal to the primary set. Secondly, the tertiary CB group is a steeply dipping subset of the primary orientation. Although the data were not collected to provide a statistically valid measure of relative abundance between the CB sets, they do also reasonably illustrate the dominance of the primary set at ~83% of all bands. 6. Tectonic interpretation Hill (1989) first suggested that high-angle deformation bands in the Aztec sandstone that do not exhibit macroscopic shear (CBs in current usage) resulted from tectonic compression related to the Sevier orogeny. His primary arguments were that the bands trend generally parallel to the encroaching thrust front and orthogonal to the east-vergent tectonic transport direction, and that they comprise the oldest structures present based on cross-cutting relationships. Subsequent workers (Taylor et al., 1999; Taylor and Pollard, 2000; Myers and Aydin, 2004; Flodin and Aydin, 2004; Eichhubl et al., 2004; Sternlof et al., 2004, 2005, 2006) have all come to the same conclusion and we concur, offering a more in-depth examination of the evidence and implications below. 6.1. Timing, spatial and material constraints The analysis of Taylor and Pollard (2000) demonstrates that CBs were already present in the Aztec to influence the initial upward and eastward expulsion of reducing basinal brines from beneath the advancing Sevier thrust front, which bleached the middle and upper parts of the sandstone as observed today (Eichhubl et al., 2004) (Figure 1.1). Thus, CBs formed in the sandstone while it was stained uniformly red with hematite grain coatings, suggesting that this trace (~1% by volume) cement (Flodin et al., 2003; 28
(a) (c) P P S T S T Figure 1.9. Stereograms for combined orientation data (equal area, lower hemispheric projections). P = primary set, S = secondary set, T = tertiary set, n = 484. (a) Normals to the band planes. (b) Density contours of planar normals (2.5% contour interval). (c) Rose diagram of strike azimuth data. (d) Rose diagram of dip azimuth data. Table 1.1. Summary of compaction band orientation data Primary Set (P) (n = 401) P Secondary Set (S) (n = 61) S T S T Tertiary Set (T) (n = 22) (b) P (d) Control Set (n = 33) Azimuth mean 81.7° 337.8° 241.2° 116.9° median 82.0° 338.0° 245.0° 116.0° standard dev. 13.3° 6.7° 11.5° 6.7° Dip angle mean 68.7° 56.9° 80.7° 61.6° median 69.0° 62.0° 80.5° 62.0° standard dev. 6.7° 13.6° 6.2° 4.9° Dihedral angles mean data median data P to S 89.4° 88.2° P to T 36.6° 34.8° S to T 89.6° 88.2° P to Control 32.6° 31.6° Rel. abundance 82.9% 12.6% 4.5% na 29
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 42 and 43: Eichhubl et al., 2004) did not lend
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
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2005). It consists of a long (infin
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⎡ ∆ ⎤ ⎧ p 1 ∆ ⎛ M ⎞
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which point the inelastic strain ha
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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
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Viewed individually, CB traces tend
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(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
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Normalized stress magnitude 3 2.5 2
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helps to explain why the oblique ap
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and ts = G·ds + H·dn (2) where tn
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plastic compaction, as suggested by
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To determine the sensitivity of pro
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segments will self-correct to provi
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6.3. Approaching tip interactions A
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0.2 0.15 0.1 0.05 0 −0.05 −0.1
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0.2 0.15 0.1 0.05 0 −0.05 −0.1
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the hooking patterns commonly obser
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(a) (b) (c) σ1 compaction band max
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σ 3 σ 2 σ 1 Figure 4.24. Schemat
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NV UT CA AZ Park Road Map Detail Pa
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compaction band Figure 5.2. Typical
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3. Computational method The methodo
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compaction band A 5 mm A‘ compact
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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,
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effective permeability represents a
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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) (
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6.1. Parallel Effective permeabilit
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By contrast, band-parallel effectiv
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Relative Effective Permeability 1.0
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(a) (b) (c) 0 meters 3 = 10-2 kb /k
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Though grossly systematic, anastomo
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168
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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
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The finite volume discretization fo
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isotropic) can lead to numerical di
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5. Simulations Three sets of 2-D si
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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
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Case 1 Case 1 Case 1 (a) (b) (c) In
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5.2.2. Discussion The elliptical pa
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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
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Bakke, S., and Øren, P. E., 1997,
Page 216 and 217:
Carpenter, D. G., and Carpenter, J.
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Eichhubl, P., Taylor, W. L., Pollar
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Karimi-Fard, M., Durlofsky, L. J.,
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-, 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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