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

(e) (f) (c) 500µm compaction band trend depositional bedding N 0 1 km (a) (b) ~ 10 mm compaction band 20 compaction band trend 500µm (g) (d)
Figure 1.4. (opposite page) Photo collage depicting compaction bands in the Aztec sandstone. (a) Study area air photo from Figure 1.1 with arrows indicating approximate locations where other photos were taken. (b) Photomicrograph mosaic of a compaction band at high angle to depositional bedding, which passes through the band with no apparent shear offset, change in direction or change in thickness (white grains are quartz, dark grains are mostly stained orthoclase and some hematite, blue is epoxy-filled pore space. (c) Backscatter electron image (BEI)from just outside the compaction band (light gray is quartz, off-white is orthoclase, dark gray is kaolinite, stark white is hematite, black is pore space). (d) BEI from inside the compaction band. Note the abrupt drop in porosity, pore size and pore connectivity accommodated by intense damage to some quartz grains. This damage, and attendant grain interpenetration, is predominantly due to pervasive microfracturing. (e) Close-up view of compaction band fin capturing its essential tabular-planar aspect, cm thickness and lack of obvious shear displacement. (f) Typical view of subparallel, anastomosing compaction band array (resistant fins) in outcrop. View is north-northwest along the dominant trend). (g) Cross-hatch pattern formed by two distinct band orientations at high angle to each other. Bands belonging to the dominant trend set (view is northward) pass through both the upper and lower crossbed boundaries, while the secondary set of bands is constrained within the middle bedding package. reduction—from ~25% and ~1,500mD in the sandstone to ~10% and 1.5 mD in the bands (Sternlof et al., 2004; Sternlof et al., 2006; Chapter 5 this thesis). In outcrop, individual CBs appear to be grossly penny-shaped and elliptical in profile, ranging in maximum thickness up to a few cm (averaging ~ 1 cm) and in length to more than 100 m. They often exhibit well-defined, elliptically tapered tips, and a variety of meter-scale patterns of near-tip interactions that are diagnostic of in-plane propagation as anticracks (Sternlof et al., 2005; Chapter 4 this thesis). By far the dominant pattern at the outcrop-scale, however, is an anastomosing planar fabric trending north-northwest and dipping steeply eastward (Figure 1.4f). Spacing between adjacent bands within this fabric can vary from 1 mm to several meters, averaging ~0.7 m (based on 286 m of orthogonal scan lines intersecting 423 bands at 23 locations—see Section 5 below). Also distinctly notable, although relatively rare and spatially isolated, are patterns of CBs that cross and sometimes turn into each other at high angle (Figure 1.4g). These “cross-hatch” patterns (Sternlof et al., 2004) are comprised of through-going bands belonging to the dominant orientation set, and a subsidiary local set trending generally southwest, dipping steeply northwest and spaced ~1.2 m on average (based on 73 m of scan lines intersecting 61 bands at 5 locations). Bands from these two sets generally cross-cut each other at a 21
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 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
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
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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
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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,
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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
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Shipton, Z. K., and Cowie, P. A., 2
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Wong, T. F., David, C., and Zhu, W.
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