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compressive stress. These results are consistent with
calculations by Simonson et al. (1976)3 which also show
that a boundary layer of higher minimum compressive stress
should restrict fracture growth. In addition, experimental
studies by Daneshy (1978)5 suggest that fracture contain-
ment may be more a result of the nature and shear strength
of the layer interface rather than any difference in mate-
rial properties on either side of the interface.
These previous studies indicate that there are at
least three parameters which may control fracture growth
in layered rock: 1) differences in the mechanical pro-
perties of the formations on either side of the interface,
2) changes in the horizontal stress state across the inter-
face, and 3) shear strength of the interface. To date,
no systematic experimental work has been done incorporating
all three of these parameters for the purpose of determin-
ing their relative influence on vertical fracture growth
and possible fracture containment in layered rock.
Accordingly, we have conducted laboratory experiments
and elastic finite element studies which clearly show that
fracture propagation in layered rock is strongly influenced
by all three parameters in a consistent and predictable
manner. First, containment can occur whenever the shear
strength of the layer interface is sufficiently weak rela-
tive to the tensile strength and the minimum horizontal
compressive stress of the bounding layer that the fracture
more easily becomes an interfacial fracture than extending
across the interface into the bounding layer. The second
and more important condition for containment is due to
a compressional increase in the minimum horizontal stress
in the bounding layer. Differences in elastic properties
of the formations in a dilithologic layered rock sequence
may be the dominant factor in determining the horizontal
stress state in individual layers with a possible compres-
sional increase in the horizontal stress in going from
high shear modulus to low shear modulus layers.
EXPERIMENTAL PROCEDURE
Hydraulic fracture experiments were conducted on rec-
tangular composite 3-layer specimens 24 cm in length,
20 cm thick, and 20 cm wide (Figure 1). The individual
layers were 8 cm in length. The composite specimen has
a 0.68 cm borehole in its center, with the axis of the
borehole perpendicular to the layer interfaces. A hollow
steel packer (0.65 cm in diameter and 13 cm long with a
0.22 cm injection hole) was inserted 11 cm into the bore-
hole and cemented by expoxy. A solid steel packer (0.65
cm in diameter and 11 cm long) was cemented by epoxy into
the other end of the borehole, leaving a 2 cm open-hole
section in the center of the middle layer. This specimen
configuration assured fracture initiation in the central
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Teufel, L. W. & Clark, J. A. Hydraulic-fracture propagation in layered rock: experimental studies of fracture containment, article, January 1, 1981; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1184461/m1/5/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.