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

~ 62 m compaction band trend 500µm Band tip Band tip Figure 3.1. Anatomy of a compaction band in the Aztec sandstone. (top) Archetypical fin exposed in outcrop from tip-to-tip (15 mm max thickness). (bottom) Backscatter electron images of the uncompacted sandstone (left) and CB (right). Quartz is medium gray, feldspar is dirty white, clay is dark gray, hematite is bright white and porosity is black. Note intense microfracture-accommodated plasticity of grains common in the band. These images were collected from the same thin section collected across the band. 76
importance to applications because of their effect on permeability. Both field (Sternlof et al., 2004; Taylor and Pollard, 2000) and laboratory measurements (Holcomb and Olsson, 2003; Vajdova et al., 2004) have shown that the permeability for flow across CBs is as much as several orders of magnitude smaller than that of the surrounding (host) material. Consequently, the formation of CBs in subsurface porous formations can strongly affect applications involving the injection or withdrawal of fluids, such as petroleum production, CO 2 sequestration, contamination clean-up and aquifer management. Viewed as two-dimensional profiles in outcrops of Aztec sandstone, individual CBs are generally long (10s of meters), thin (a few centimeters) zones of grains compacted through inelastic processes of porosity loss, primarily grain fracture and rearrangement (Figure 3.1). These CBs appear to have propagated outward along planes roughly orthogonal to the direction of maximum remote compressive stress (Sternlof et al., 2005). Experimental efforts to induce compaction localization in sandstone cylinders under axisymmetric compression (Olsson, 1999; Olsson and Holcomb, 2000; Baud et al., 2004; Klein et al., 2001) have tended to produce zones of compaction that appear to occur nearly instantaneously across the width of the specimen indicating that propagation, if it occurs, does so rapidly. On the other hand, in triaxial simulations of bore hole breakouts in sandstone (Haimson, 2001; Hamison and Lee, 2004; Klaetsch and Haimson, 2002), the tips of features resembling CBs have been identified extending from elongated, slot- shaped breakouts. In order to examine band propagation in the laboratory, Vajdova and Wong (2003) and Tembe et al., (2006) and conducted axisymmetric compression experiments on cylindrical specimens with an external, circumferential notch. In some cases, they observed compaction initiating at the notch and extending across the specimen in increments corresponding to small load drops. A critical element in reconciling different laboratory observations, differences between laboratory and field observations, and in making predictions for practical applications is a better understanding of conditions for propagation. Although theoretical studies (Olsson, 1999; Issen and Rudnicki, 2000, 2001; Detournay et al., 2003; Bésuelle and Rudnicki, 2004; Rudnicki, 2002, 2003, 2004) have had some success in identifying stress conditions and material behavior that are favorable for CB formation, there is less understanding of the conditions for propagation or arrest. Sternlof and Pollard (2002) and 77
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STRUCTURAL GEOLOGY, PROPAGATION MEC
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Abstract Low-porosity, low-permeabi
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delivered with fortitude, humor, su
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Chapter 3—Energy-release model of
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List of Illustrations Figure A. Cov
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Figure A. Cover photo that accompan
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likely present in subsurface sandst
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hooking-tip interactions—using th
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and sandstone, my co-authors—Moha
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the hard data from which accurate p
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Although the Aztec sandstone experi
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Waterpocket Fault 36 o 26‘ N 0 1
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Cenozoic Mesozoic Paleozoic Quatern
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3.3. Deformation The Aztec also has
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There also are relatively high-angl
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(e) (f) (c) 500µm compaction band
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dihedral angle of 80° or more, and
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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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Page 84 and 85: concentration of quartz plasticity
Page 86 and 87: conducted on well-cemented sandston
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
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Page 100 and 101: interact is inversely proportional
Page 102 and 103: (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.
Page 108 and 109: 1973; Mardon, 1988; Peck et al., 19
Page 110 and 111: undamaged host rock. That CBs canno
Page 112 and 113: 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
Page 124 and 125: 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
Page 134 and 135: (a) (b) (c) σ1 compaction band max
Page 136 and 137: 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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