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

P (a) (c) S P S Figure 1.10. Stereograms for restored orientation data (equal area, lower hemispheric projections0. P = primary set, S = secondary set, n=484. All orientation data were rotated 25° counterclockwise about an axis with azimuth 315° (NW) and plunge of 0°, in order to restore them to pre-tilting attitudes. (a) Normals to the band planes. (b) Density contours of planar normals (2.5% contour interval). (c) Rose diagram of strike azimuth data. (d) Rose diagram of dip azimuth data. Table 1.2. Summary of restored compaction band orientation data Primary Set (P) (n = 423) P S Secondary Set (S) (n = 61) S (b) (d) P Control Set (n = 33) Azimuth mean 89.9° 317.9° 116.9° median 91.9° 320.4° 116.0° standard dev. 16.9° 12.0° 6.7° Dip angle mean 51.7° 51.2° 61.6° median 51.2° 55.2° 62.0° standard dev. 9.1° 12.1° 4.9° Dihedral angles mean data median data P to S 88.8° 86.2° P to Control 24.5° 22.7° Rel. abundance 87.4% 12.6% na 32
otated all of the CB orientation data 25° counterclockwise about an axis trending 315° (northwest) and plunging 0°, in keeping with available bedding orientation data for the Cretaceous units (Bohannon 1977, 1983). The restored data are presented graphically in Figure 1.10 and summarized in Table 1.2. The most obvious result of the restoration is that the 22 measurements originally attributed to a distinct third set of CBs trending northwest and dipping steeply southwest (also previously identified by Hill, 1989 and others) can reasonably be categorized as falling within the periphery of the primary (dominant) orientation group. This leaves just two sets of CBs with mean orientations that are essentially orthogonal (dihedral angle of 88.8°). On average, the dominant set trends due north and dips 52° east, while the secondary set trends almost due northeast and dips 51°northwest. The axis of intersection between these mean CB orientations—azimuth of 24° and plunge of 27°—represents the approximate line of σ3, which turns out to be more nearly horizontal than vertical. The inferred azimuth/plunge directions of all three paleostresses are: 270°/38° (σ1), 138°/39° (σ2) and 24°/27° (σ3) (Figure 1.11a). These inferred paleostress directions represent approximate estimates, both because σ1 and σ2 (the poles to the dominant and secondary mean CB orientations) are not quite orthogonal (88.8°), and as a result of the scatter in the raw orientation data (± 17° in azimuth and 12° in dip) (Table 1.2). 6.3. Geomechanical implications The radical departure of our inferred paleostress state from the classic Andersonian expectation that one of the principal stress components is always subvertical, σ3 in thrust- faulting environments (Anderson, 1951) means one of three things: the reconstruction of the paleo CB orientations is faulty and the two sets were actually subvertical as well as orthogonal; the underlying interpretation of CBs as anticracks is incorrect and they do not reflect the orientations of the principal paleostresses; or the analysis is correct and points to an as yet unrecognized regional tectonic explanation. We address the two former possibilities first. While our first-order approach to the reconstruction is certainly approximate, it is fundamentally sound and anything more complex is currently unwarranted given the available data. The best way to refine the reconstruction would be to collect a high density of bedding orientation data as stratigraphically low in the Cretaceous deposits as 33
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 32 and 33: (e) (f) (c) 500µm compaction band
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 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
Page 82 and 83: MPa 10 4 10 3 10 2 10 1 10 −5 10
Page 84 and 85: concentration of quartz plasticity
Page 86 and 87: 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 ⎞
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which point the inelastic strain ha
Page 98 and 99:
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
Page 130 and 131:
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,
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
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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