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

NV UT CA AZ Park Road Map Detail Park Boundary * Route 169 0 5 km NEVADA ARIZONA 10 km Valley of Fire State Park N LAKE MEAD 115 o 30' Figure 5.1. Schematic location map for the Valley of Fire State Park in southeastern Nevada. Colorful alteration patterns of iron-oxide staining in the Aztec sandstone lend the park its name (* marks approximate location of photographs shown in Figures 5.2 and 5.3). 126 36 o 15'
and Pollard 2000; Lothe et al. 2002), rendering them impediments to fluid flow under saturated conditions (Figure 5.2). Sternlof et al. (2004) have shown that anastomosing arrays of subparallel, subvertical CBs abundantly exposed in the Aztec sandstone (Figure 5.3) would significantly reduce bulk permeability and induce permeability anisotropy at outcrop scales. Part of a widespread Jurassic æolian system that includes the Navajo and Nugget sandstones (Marzolf 1983; Blakey 1989), the 1,400-m-thick Aztec is a medium-grained sub-arkose that is typified by large-scale cross stratification (Bohannon 1983) and comprises an exhumed analog for aquifers and reservoirs in similar lithologies. The pervasive CB arrays, which cut across depositional bedding as the oldest structural fabric present, formed in response to compression associated with the Cretaceous Sevier Orogeny (Hill 1989; Eichhubl et al. 2004; Sternlof et al. 2005). If present in an active aquifer or reservoir, these band arrays would cause substantial fluid-flow effects at scales relevant to production and management (Sternlof et al. in review). The specific hydraulic impacts exerted by CBs depend strongly on their porosity and permeability relative to the surrounding sandstone matrix, as well as on geometrical factors such as average band thickness, spacing and connectivity (Sternlof et al. 2004). Their limited thickness, however, renders direct measurement of CB permeability difficult and potentially inaccurate under even optimal conditions (Antonellini and Aydin 1994). Given the generally limited availability of potentially unconsolidated core samples from active aquifers and reservoirs, problems proliferate. Methods for estimating permeability from epoxy-impregnated thin-sections using computational techniques provide an alternative (e.g. Berryman and Blair 1987; Adler et al. 1990; Bakke and Øren 1997; Blair et al. 1996). In this paper, we evaluate a new physics-based algorithm for estimating permeability from thin section images (Keehm et al. 2004). In order to simulate the realistic situation of limited subsurface sample supply, we apply the method to a single, representative thin section from the Aztec (Figure 5.4) and compare the resulting estimates of CB and matrix permeability to available measurements reported for the Navajo and Aztec sandstones (Antonellini and Aydin 1994; Flodin et al. 2005). 127
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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
Page 88 and 89: ~ 62 m compaction band trend 500µm
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
Page 98 and 99: they can exert significant effects
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
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 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
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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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