Microstructural effects on the unconfined mechanical behavior of a tectonically deformed calcareous shale, a study case in the Santiago Formation, Mexico
Por:
Jimenez Camargo, Jubier Alonso, Cerca, Mariano, Carreon-Freyre, Dora
Publicada:
1 oct 2022
Resumen:
Microstructural properties play a crucial role in the mechanical
response of shale rocks. This work examines the impact of fabric
anisotropy on the strength and elastic behavior of a highly deformed
Jurassic calcareous shale from the Santiago Formation in eastern Mexico
by means of unconfined compression strength tests (UCS). The Santiago
Formation is attracting considerable interest for the development of
unconventional resources of shale gas and shale oil in Mexico. However,
the effect of tectonic deformation on the mechanical properties of these
Mexican Shales has not been addressed in detail. The anisotropy of the
shale was evaluated by means of rock samples cored in the direction
normal to layers and two horizontal directions defined along the
foliation planes. Petrography of oriented thin sections, X-ray
diffraction, scanning electron microscopy (SEM), and petrophysical
properties (porosity and permeability), were used to assess the rock
composition and microstructural properties. UCS tests results revealed
different mechanical responses between the normal direction (V) and the
direction parallel to layers, but also differences between the two
mutually orthogonal horizontal directions (H1, H2). Tangent Young's
modulus (E) showed higher values in the H2 direction (13-22 GPa) and
lower values in the H1 and V directions (8-10 GPa). All the specimens
yielded very low Poisson's ratios (<0.11). H2 samples displayed the
highest strength (48-84 MPa) and reached higher axial strains at failure
(0.4-0.7%). Specimens in the H1 direction presented the lowest strength
and axial strains (15-29 MPa and 0.22-0.35%, respectively). Compared to
H1 samples, vertical samples yielded slightly higher strengths (26-33
MPa) and axial strains (0.31-0.40%). The results reported here confirm
that microstructure strongly influenced the mechanical anisotropy and
fracture mechanisms of the Santiago Shale. A direct relation was
documented between fabric anisotropy, elastic response, UCS, and brittle
failure modes validating the importance of fabric characterization for a
complete description of anisotropy in tectonically deformed shale rocks.
Filiaciones:
Jimenez Camargo, Jubier Alonso:
Univ Nacl Autonoma Mexico, Posgrad Ciencias Tierra, Ctr Geociencias, Blvd Juriquilla 3001, Juriquilla 76230, Queretaro, Mexico
Cerca, Mariano:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Blvd Juriquilla 3001, Juriquilla 76230, Queretaro, Mexico
Carreon-Freyre, Dora:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Blvd Juriquilla 3001, Juriquilla 76230, Queretaro, Mexico
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