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

By contrast, band-parallel effective permeability is not reduced by an order of magnitude until wb/W=90%, a DB volume density far exceeding the approximate upper limit of 20% observed in the Aztec. Thus for parallel DB patterns within the realistic wb/W range, a permeability anisotropy of up to 2 orders of magnitude can be expected, with the maximum permeability oriented in the band-parallel direction (Figure 6.9). Note also that band-parallel effective permeability for both kb/km=10 -2 and 10 -3 are virtually indistinguishable below wb/W=80%. 6.2. Cross-hatch Cross-hatch DB sets in the Valley of Fire exhibit a consistent acute intersection angle of ~80°. In other locales, intersection angles ranging from ~20° to ~90° have been reported (Aydin and Reches, 1982; Hill, 1989; Jamison and Stearns, 1982; Underhill and Woodcock, 1987). We begin our analysis of the effective permeability of cross-hatch patterns by studying those of evenly spaced, orthogonal DB sets as a function of kb/km and wb/W. Figure 6.10 compares our numerical modeling results for kb/km=10 -2 to an analytical approximation presented by Taylor and Pollard (2000) and band-normal effective permeability as calculated by harmonic averaging. The numerical and harmonic averaging results match well over the entire wb/W range, but correspond to the analytical approximation only for wb/W below about 5%. For kb/km=10 -3 the wb/W range of correspondence drops to
Relative Effective Permeability 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 Taylor and Pollard (2000) Numerical Model Harmonic Average 0 10 20 30 40 50 60 70 80 90 100 Volume Fraction Deformation Bands (%) Figure 6.10. Isotropic effective permeability for cross-hatch patterns of evenly spaced, perpendicular DB sets as a function of DB volume fraction for the DB/sandstone matrix permeability ratio of 10 -2 . Results from the finite difference-finite element method used in this paper (FD-FE) modeling are plotted against both the analytical approximation of Taylor and Pollard (2000) and the permeability computed normal to just one of the DB sets using the harmonic averaging method. The FD-FE and harmonic averaging methods agree well over the entire volume fraction range, while the approximation holds only for volume fractions up to about 5%. The range of DB volume fraction observed in the Aztec sandstone is highlighted in gray. 161
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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
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n = 20 M n = 20 P n = 22 B n = 20 R
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were encountered, giving the dihedr
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Eichhubl et al., 2004) did not lend
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P (a) (c) S P S Figure 1.10. Stereo
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possible, and use these to better c
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1.5(ρgz) (b) WEST Willow Tank Uppe
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9. Acknowledgements My sincere than
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The term compaction band (CB) was c
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Pollard, 2002). The particular util
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Hue-based image analysis using MATL
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a direct genetic relationship (Hill
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Compaction band fin Depositional be
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suggests—that to first approximat
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Porosity Porosity 0.3 0.25 0.2 0.15
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pore-clogging clay—due presumably
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500 µm Figure 2.9. Electron backsc
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(a) (b) σ 3 σ 1 x 3 x 1 x 1 (c) u
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6. Elastic properties Despite a lon
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Comparison of the two approaches es
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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
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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
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
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
Page 144 and 145: compaction band A 5 mm A‘ compact
Page 146 and 147: 4. Application to the Aztec sandsto
Page 148 and 149: Permeability (mD) 10 4 10 3 10 2 10
Page 150 and 151: B‘ A‘ A c f m c m c f c f c f c
Page 152 and 153: 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
Page 158 and 159: Commonly from ~1 mm to ~1.5 cm in t
Page 160 and 161: Although systematic arrays of DBs p
Page 162 and 163: to 2 m, with both sets in a cross-h
Page 164 and 165: y identical blocks all subject to t
Page 166 and 167: contiguous areas. This type of char
Page 168 and 169: (0,b) n 3 (0,0) f 2 n 2 n 1 (a,0) (
Page 170 and 171: 6.1. Parallel Effective permeabilit
Page 174 and 175: 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
Page 184 and 185: compaction band trend 500µm Figure
Page 186 and 187: Cover Outcrop Band N 100 meters 20
Page 188 and 189: (CBs) and the matrix rock in all si
Page 190 and 191: The finite volume discretization fo
Page 192 and 193: 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.
Page 198 and 199: 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
Page 206 and 207: (a) (b) Leak 200 meters Regional gr
Page 208 and 209: anticipated sustainable pumping rat
Page 210 and 211: Finally, there is the issue of fore
Page 212 and 213: 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.,
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-, 1987, Fracture from a straight c
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Shipton, Z. K., and Cowie, P. A., 2
Page 226:
Wong, T. F., David, C., and Zhu, W.
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