Mineralogical characterization and strain analysis of the Marcellus shales

Due to the complex structure of the brittle formations like shale, their microcracking and mechanical deformation behavior are not well known. To understand the fundamental factors at the micron scale, Marcellus shales were cored both parallel and perpendicular to the bedding orientation and mechani...

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Bibliographic Details
Published in:International journal of rock mechanics and mining sciences (Oxford, England : 1997) England : 1997), 2020-06, Vol.130, p.104345, Article 104345
Main Authors: Yakaboylu, Gunes A., Gupta, Neel, Sabolsky, Edward M., Mishra, Brijes
Format: Article
Language:English
Subjects:
Calcite
Crack initiation
Creep
Creep tests
Crystal defects
Deformation
Fracture mechanics
Heterogeneity
Kerogen
Lattice strain
Macrostrain
Marcellus shale
Mechanical properties
Microcracking
Microcracks
Microstrain
Mineralogy
Organic matter
Raman spectroscopy
Shale
Shales
Strain
Strain analysis
X-ray diffraction
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Summary:Due to the complex structure of the brittle formations like shale, their microcracking and mechanical deformation behavior are not well known. To understand the fundamental factors at the micron scale, Marcellus shales were cored both parallel and perpendicular to the bedding orientation and mechanically tested through triaxial creep test under constant stress. The parallel-bedded shales exhibited higher level of permanent strain in the radial direction, which increased with increasing time. This also confirmed their anisotropic nature due to the bedding. Their advanced characterization via X-ray diffraction (XRD) and Raman spectroscopy techniques before and after the creep tests revealed the mineralogical heterogeneity, and the presence of an organic matter (kerogen) concentrated in the microcrack areas. Besides, the XRD peak shifts and changes in peak shape indicated that there was a certain level of macrostrain and microstrain in the shale. Further investigation of the XRD peak shape (integral breadth) changes using the Williamson-Hall method demonstrated a higher concentration of lattice defects and associated microstrain (inhomogeneous lattice strain) present in the calcite phase compared to the quartz. The parallel-bedded shales also revealed a higher level of microstrain with respect to the perpendicular-bedding. The results proved that the microcracking (initiation and propagation) and associated mechanical deformation of the Marcellus shales were mostly influenced by the presence of organic matter, microstrain level (defect concentration) in the calcite mineral, and the bedding orientation.
ISSN:1365-1609
1873-4545
DOI:10.1016/j.ijrmms.2020.104345