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The Effect of Bedding Laminations on Crack Propagation in the Marcellus Shale

Evan McMullen
University of Maryland, College Park

In this study I conducted deformation experiments on three Marcellus Shale samples, to investigate the effect of laminations on crack propagation. Cylindrical samples were used in the mechanical test. Two of the samples were taken parallel to the bedding planes, and one was taken perpendicular to the bedding planes. Prior to the deformation tests, initial porosity and permeability of the undeformed samples were measured. At the confinements and strain rates used in the study, all three samples failed by brittle fractures. Porosity and permeability measurements were then conducted on the deformed samples. By mechanically fracturing the samples, permeability and crack networks have been enhanced due to the internal features of the shale. I also performed microstructural analysis of undeformed and deformed samples. Comparison of the mechanical data and microstructure of bedding parallel to bedding perpendicular samples supports my hypothesis that the bedding orientation relative to stress orientation affects crack propagation. I also observed that crack growth is not only affected by the thin laminations, but also the strength contrast between silt-sized particles and clay minerals in these Marcellus Shale samples.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013