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

Waterpocket Fault 36 o 26‘ N 0 1 km 114 o 32‘ Willow Tank Thrust Park Road Overton Syncline Lower Aztec 12 Oregon Washingto n California 30 Nevada Canada Las Vegas Idaho Air photo detail Valley of Fire Cretaceous units 25 Upper Aztec Park Office 25 Montana Utah Wyoming Arizona Baseline Fault Route 169
Figure 1.1 (opposite page) Location and general geology of the study area in the Aztec sandstone at the Valley of Fire State Park, southeastern Nevada. The Aztec crops out as a 1,400-m-thick sequence of gently folded, northeasterly dipping (~25°) æolian deposits consisting of ~800 m of red-stained sandstone (lower Aztec) and ~600 m of bleached and variegated sandstone (upper Aztec). The Aztec is immediately, though unconformably overlain by up to 1,300 m of Cretaceous deposits (principally the quartz-rich Baseline sandstone in the air photo). The Aztec has been extensively affected by Basin and Range extension, principally by north-northeasterly trending left-lateral strike slip-faults and subsidiary northwesterly trending right-lateral strike-slip faults (apparent in the many offsets of the red/buff alteration front). The major left-lateral bounding faults for the immediate study area (Waterpocket fault and Baseline fault) are indicated (after Bohannon 1983), as are the Overton Syncline (after Carpenter and Carpenter, 1994) and two representative bedding orientations in the lower Cretaceous units (after Bohannon, 1983). Less obvious are remnants of the east-vergent Willow Tank thrust (upper right corner, teeth denote hanging wall), marking the easternmost extent of compressional tectonism related to the Cretaceous Sevier ororogeny. The aerial photo base is a mosaic constructed of images downloaded from Google Earth. Within the general vicinity of the Valley of Fire (Figure 1.1), the 1,400-m-thick Aztec unconformably overlies terrigenous clastic, evaporitic and limestone deposits of the Triassic and Permian, which themselves unconformably overlie miogeoclinal carbonates of Pennsylvanian age and older. The Aztec in turn is unconformably overlain by up to 1,300 m of upward-coarsening Cretaceous clastics and, following a depositional hiatus through the Paleogene, another 300 m of Neogene limestones and clastics (Bohannon, 1983; Bohannon et al., 1993; Eichhubl et al., 2004). Figure 1.2 presents a generalized stratigraphic section of the region from latest Paleozoic time through the present day, as modified from Bohannon (1977). The Aztec sandstone itself is a subarkose containing up to 8% orthoclase and minor amounts of lithic fragments (Eichhubl et al., 2004). It is composed of moderately rounded, fine to medium-sized detrital grains (0.1 to 0.5 mm, 0.25 mm average) arranged in a large-scale wedge and tabular-planar cross stratified sedimentary architecture characteristic of æolian deposition (Marzolf, 1983). The Aztec is generally quite friable, with porosity averaging about 20-25% (Sternlof et al., 2005) and permeability ranging from about 100 to 2,500 mD (Flodin et al., 2005; Chapter 5 this thesis). Clay, chiefly kaolinite, comprises up to 6% of the rock by volume and forms the predominant grain- bridging, pore-filling cement. 13
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 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 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
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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
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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,
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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
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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