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The creation of a sub-porosity
by sediment deposition within a fracture is
controlled by the aperture and flow path geometry
and the volumetric flow rate. An acoustic lens
system was used to produce a pseudo-collimated
wavefront with a controllable beam diameter to
define field of views of 5 mm, 20 mm and 60 mm.
Based on analysis of the of the seismic signals
measured, frequency independent stiffness is not
sufficient to indicate homogeneity in fracture
properties alone. Frequency dependent stiffness
indicates that a probability distribution of
fracture specific stiffness exists in a fracture.
How the observed relationship between fracture
specific stiffness and frequency changes with
increasing scale of observation determines the
existence of a spatial distribution of fracture
specific stiffnesses. The research delineates
competing effects from scattering caused by both
probability distributions and spatial distributions
in fracture specific stiffness.
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The ability to distinguish
open fluid-filled fractures from those partially
filled by a
sub-porosity depends on the aperture of the
fracture, the size of the grains composing the
subporosity, the relative thickness of the
sub-porosity layer to the thickness of the
water-layer and the wavelength of the seismic
signal. If seismic techniques are to be
developed to monitor the injection and containment
of phases in sequestration reservoirs or the
propping of hydraulically induced fractures to
enhance oil and gas production, it is important to
understand how a sub-porosity within a fracture
affects macroscopic seismic and hydraulic
measurements.
For additional details, see:
Acosta-Colon, A.A., and Pyrak-Nolte., L.J. 2007,
Detecting the Presence of a
Sub-Porosity in an Open Fluid-Filled Fractures. Eos
Trans. AGU, 88(52), Fall Meet. Suppl., Abstract
H11B-0485.
Pyrak-Nolte, L.J., 2007, Fracture anisotropy: The
role of fracture-stiffness gradients. The Leading Edge, 26, 1124-1127,
DOI:10.1190/1.2780781.
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