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

and sandstone, my co-authors—Mohammad Karimi-Fard, David Pollard and Louis Durlofsky—and I were able to model the impact of the bands for a variety of practical scenarios: well-pair pump testing, five-spot reservoir production and contaminant plume migration. Our results confirm that the anastomosing band pattern as mapped would exert significant pressure drop and directional fluid transport effects over hundreds of meters. In addition to conceiving of the project, I conducted all of the fieldwork and photo mapping (including arranging for additional air photos to be taken), designed the five- spot and plume scenarios modeled, and produced all the text (except for the Flow Model section) and final figures. Karimi-Fard ran the flow simulations—an arduous task—using a model code previously developed, primarily by him. He also collaborated closely in designing the simulation scenarios and figures, wrote the Flow Model section, and participated in every sense as an equal research partner. Pollard and Durlofsky provided guidance and thorough editing. This paper has been accepted for publication in Water Resources Research and is currently in press. This introduction would not be complete without touching on my experimental efforts and collaborations, which failed to bear publishable fruit in time for inclusion in this dissertation, but did add about a year to my tenure at Stanford. The desire to test the anticrack CB mechanical interpretation in the lab, and by so doing shed light on the enigmatic nature of CB tip-zone processes, was irresistible to me—practical timing concerns voiced by my committee notwithstanding. Besides, as mentioned above in the introduction to Chapter 3, it seemed that experimental compaction localization research, which had already become a hot area, was headed in a direction at odds with observable natural reality. In forging ahead despite my committee’s accurate admonitions, I did manage to glean valuable “negative result” insights into the balance of material and loading conditions conducive to CB formation. Specifically, I suggest that natural compaction bands, such as observed in the Aztec, form in unconsolidated to barely lithified porous sands subjected to tectonic and burial stress states typical of the shallow crust. Despite using weakly lithified Aztec specimens in my experiments, which I seeded with stress-concentrating flaws and loaded uniaxially over a range of geologically plausible confining pressures, failure invariably occurred by dilational shear. On the other hand, experiments that force compaction to occur in lithified sandstone at mid-crustal 6
confining pressures produce, in my opinion, a failure phenomenon distinct from compaction banding as observed in outcrop. The greater value of my fledgling laboratory efforts probably lies in the collaborative relationships developed within the experimental community pursuing compaction localization research. I visited and worked in the labs of Bezalel Haimson (University of Wisconsin-Madison), William Olsson and David Holcomb (Sandia National Labs) and David Lockner (USGS-Menlo Park), and corresponded extensively with the laboratory of Teng-fong Wong (Stony Brook University). Through these interactions and a DOE- sponsored workshop (October 2004), which led directly to my association with co-author John Rudnicki (Chapters 2 and 3), David Pollard and I have introduced a much-needed field-based reality check into compaction localization experimentation. Whether this influence will become more tangible through my own future experimental efforts remains to be seen. Finally, I would be remiss in not observing that, although a strong process-based mechanics perspective and approach pervade this thesis, it is based primarily on observations made from outcrops and samples of the Aztec sandstone. While this fact does not detract from my results and interpretations, the issue of ubiquity is relevant from a practical applications standpoint. That is, are CB arrays such as observed in the Aztec common in sandstone aquifers and reservoirs, or are they a relative freak of nature? From a fundamental physical and mechanical point of view, it is unlikely that CBs in the Aztec represent an isolated phenomenological fluke. However, shear deformation bands have been observed in a wide variety of clastic deposits exposed around the world, and similar observations of CBs are needed to confirm them as a common structure in porous sandstone. Beyond this obvious direction for future analog reservoir-based fieldwork, a concerted effort also is needed to develop borehole geophysical methods for detecting and characterizing deformation bands of all types in the subsurface. The general petrophysical attributes of bands should, in theory at least, render them visible to a variety of imaging technologies, ranging from acoustic to electromagnetic. In conjunction with a solid mechanical understanding of how CBs and CB arrays form—the foundations for which are laid here in Chapters 1 through 4—such imaging techniques would provide 7
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 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 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
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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
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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.
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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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