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

100 meters 5 meters NV UT CA AZ Park Roa d Route 16 9 0 km 5 Map Detail Air Photo NEVADA ARIZON A 10 km Valley of Fire State Park N LAKE MEAD 115 o 30' Figure 7.1. Aerial photograph showing a largely bare and level outcrop area of Aztec sandstone in the Valley of Fire State Park of southeastern Nevada. The geographical location of the study area is indicated in the map (inset, upper right). A high-resolution digital scan of the negative made it possible to identify (photo inset lower left) and map (photo inset lower right) the patterns of individual, cm-thick compaction bands cropping out as distinct fins over an area of more than 150,000 m 2 . 170 36 o 15'
exert appreciable fluid flow and transport effects at scales of practical relevance to resource management in aquifers and reservoirs has remained an open question. To begin addressing this issue, we present a series of flow simulation scenarios that honor the exact details of individual compaction band arrays mapped over an outcrop area of some 150,000 m 2 (37 acres) in the Aztec sandstone of southeastern Nevada (Figure 7.1). The simulations were conducted using a discrete-feature model in which the bands are represented as one-dimensional elements assigned realistic petrophysical properties. This effort represents the application of state-of-the-art flow modeling to a data set of unprecedented detail and scale, which was derived from a real geological system that serves as an exhumed analog for active sandstone aquifers and reservoirs. Analog outcrop-based permeability and flow-modeling studies, whether focused on gross sedimentological heterogeneities (e.g. White and Barton, 1999; Stephen and Dalrymple, 2002) or on fine-scale structural features (e.g. Taylor et al., 1999; Sternlof et al., 2004), can provide valuable insights into the natural variability of inter-well flow and the balance of parameters governing optimal (or at least improved) well placement. The Aztec sandstone as exposed in the Valley of Fire State Park lies about 60 km northeast of Las Vegas (Figure 7.1, map inset). The Aztec is a fine to medium-grained, sub-arkosic æolian sandstone some 1,400 m thick, which was deposited as large amplitude cross beds in a back arc basin setting from Late Triassic to Middle Jurassic time (Bohannon, 1983; Marzolf, 1983). It exhibits a mean grain size of about 0.25 mm, porosity ranging from 15% to 25% and permeability ranging up to several Darcys (Antonellini and Aydin, 1994; Flodin et al., 2005). Extensive arrays of sub-parallel, anastomosing compaction bands (CBs) pervade the upper 600 m of the Aztec exposed over an area of more than 10 km 2 . Apparently associated with tectonism of the Cretaceous Sevier orogeny, these bands at high angle to bedding comprise the oldest structural fabric present, which subsequently was overprinted by shear bands, joints, sheared joints and strike-slip faults (Hill, 1989; Taylor and Pollard, 2000; Eichhubl et al., 2004; Flodin and Aydin, 2004; Myers and Aydin, 2004; Sternlof et al., 2005). As observed in the Aztec and similar sandstones, CBs are discrete, tabular, bounded features of porosity-loss compaction accommodated by granular rearrangement, grain crushing and chemical diagenesis that exhibit little or no net shear and tend to weather 171
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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
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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
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 172 and 173: By contrast, band-parallel effectiv
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 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.,
Page 222 and 223: -, 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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