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

Cenozoic Mesozoic Paleozoic Quaternary Permian Triassic Triassic? Jurassic Cretaceous Tertiary Miocene & Pliocene Miocene Thickness (m) 5,400 4,800 4,200 3,600 3,000 2,400 1,800 1,200 600 0 Quaternary Deposits Muddy Creek Formation Horse Spring Formation Baseline Sandstone Willow Tank Formatio n Aztec Sandstone Moenave Formation Chinle Formation Moenkopi Formation Kaibab Limestone Toroweap Formatio n Hermit Shale Lithologic Descriptions Sandstone Shale Siltstone Calcareous shale Limestone Dolomite Magnesite Conglomerate Breccia Evaporites (gypsum) Calcareous conglomerate Figure 1.2. Generalized stratigraphic column for the Valley of Fire area from the Permian Hermit shale through Quaternary alluvium (adapted from Bohannon, 1977). 14 Chert
Abundant deeply etched and/or kaolin-replaced orthoclase grains indicate that much of the clay present is internally derived (Eichhubl et al., 2004; Sternlof et al., 2005). Small amounts of inter-layered smectite and illite are also present (Eichhubl et al., 2004). Abundant mutual indentation of quartz grains via pressure solution has been reported (Flodin et al., 2003; Eichhubl et al., 2004), although much of this texture may in fact be due to mechanical indentation accommodated by pervasive intra-grain microfracturing (Sternlof et al., 2005). 3.2. Diagenesis Syndepositional precipitation of hematite grain coats resulted in the Aztec being stained a uniform red color during initial burial (Eichhubl et al., 2004). The color from this earliest diagenetic alteration still dominates the lower half of the sandstone. The upper Aztec, however, has been subjected to at least two stages of bleaching and iron oxide redistribution apparently associated with upward and eastward expulsion of reducing basinal brines from beneath Sevier-related thrust sheets advancing from the west (Eichhubl et al., 2004). These fluid-flow events are responsible for the vividly colorful patterns of iron mineralization from which the Valley of Fire derives its name (Figure 1.1). Despite its long alteration history, however, the presence of only limited quartz overgrowth cementation and diagenetic illite, both restricted to the very bottom of the pile (and within the damage zones of some major faults), indicate that the base of the Aztec in the Valley of Fire has likely never been buried deeper than about 3 km (~ 80° C for a normal geothermal gradient). Interestingly, this equals the sum of its own thickness and of all overlying sedimentary deposits through (Eichhubl et al., 2004; Sternlof et al., 2005). In any case, the Aztec is today at best moderately well cemented toward the bottom, where it is still red, and poorly cemented toward the middle and top (Flodin et al., 2003), where it has been extensively bleached and now exhibits an unconfined uniaxial compressive strength of only 2-3 MPa (Haimson and Lee, 2004). Neither is there evidence to suggest that the state of lithification anywhere in the Aztec was ever appreciably greater than it is today. Our own limited triaxial testing, however, does indicate that the resistance of present-day Aztec to uniform compaction with increasing pressure approaches that of quartzite. 15
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 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 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
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MPa MPa 80 70 60 50 40 30 20 10 0 0
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2002) and use a BEM approach (Crouc
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MPa 10 4 10 3 10 2 10 1 10 −5 10
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concentration of quartz plasticity
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conducted on well-cemented sandston
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~ 62 m compaction band trend 500µm
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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
Page 104 and 105:
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,
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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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