structural geology, propagation mechanics and - Stanford School of ...

hooking-tip interactions—using the BEM code. The degree of success attained suggests
that the linear elastic anticrack mechanical model provides a valid first approximation for
conceptualizing and simulating CB propagation. Perhaps the most interesting and
potentially useful result of this paper is the model observation that anticrack CBs respond
to high compressive normal stress (σ2 ≈ σ1) oriented parallel to their trend with
propagation-path instability. This is opposite to the instability effect observed for
opening-mode cracks (Olson and Pollard, 1989; Thomas and Pollard, 1993), and could be
used to help forecast the degree of anastomosis in subsurface CB arrays as a function of
stress history. By the same token, the configuration of an exhumed CB array could be
used to constrain the ambient principal paleostress state (orientation and magnitude) in
which it formed. For this paper, I performed all the fieldwork, modeling, writing and
figure drafting, with guidance and editing provided by second-author David Pollard. For
the modeling, I used the BEM code written by third-author Gaurav Chopra (Chapter 2).
Submission of a final manuscript based on Chapter 4 to Journal of Structural Geology is
anticipated.
Chapter 5 represents another outgrowth of my collaborative efforts, in this case with
Tapan Mukerji and Youngseuk Keehm of the Stanford Rock Physics and Borehole
Geophysics (SRB) Group. I had gone to Mukerji for help in using MATLAB® to
perform automated image-analysis measurements of porosity from my thin-sections, the
results of which contributed to every other chapter in this thesis. For the purposes of the
fluid-flow modeling presented in Chapter 7, I had also contemplated collecting
permeability measurements, but was dissuaded by the difficulty of obtaining reliable
results from thin CBs at reasonable expense. Through Mukerji, however, I learned of the
computational permeability estimation algorithm that had been developed in the SRB,
principally by Keehm, and could be used to generate virtual permeability measurements
from my existing thin sections. I recognized the opportunity to perform a practical test of
this new tool within the context of the analog reservoir research concept. Specifically, we
applied the method to my prize thin section and compared the estimation results to
available permeability measurement data for both CBs and host rock from the Aztec and
Navajo sandstones. Correspondence was excellent, suggesting that, for a subsurface
equivalent of the CB-rich Aztec from which only scarce, potentially unconsolidated
4