[First Hit]

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Origin of Anomalous Previous HitMagneticNext Hit Fabrics in the Woodford and Marcellus Shales


The anisotropy of Previous HitmagneticNext Hit susceptibility (AMS) in most shale units is characterized by a normal Previous HitmagneticNext Hit fabric where the Previous HitmagneticNext Hit foliation is parallel to the bedding plane with a distinctly oblate shape. New AMS data from the Woodford and Marcellus shales show anomalous AMS signatures with a Previous HitmagneticNext Hit foliation perpendicular to the bedding plane and a mixed prolate/oblate fabric. The acquisition of these Previous HitmagneticNext Hit fabrics may be explained by the following processes: (1) fluid filled fractures displacing adjacent ferromagnetic and paramagnetic grains; (2) bioturbation; (3) inverse Previous HitmagneticNext Hit fabrics carried by single domain magnetite or goethite; (4) granular rotation of Previous HitmagneticNext Hit carrier minerals in localized viscoplastic zones (5) and authigenic ferromagnetic and minerals formed in association with fluid events. Preliminary observations of the Woodford shale suggest that anomalous AMS fabrics are associated with localized vertical/sub vertical fluid filled fractures however, further investigation is required. Observations of the Marcellus shale indicate an association between anomalous AMS fabrics and localized viscoplastic zones. Paleomagnetic and rock Previous HitmagneticNext Hit investigations reveal that the dominant Previous HitmagneticNext Hit carrier mineral is magnetite for both shale units. The degree of anisotropy (P′) in both the Woodford and Marcellus shales increases with depth, suggesting fabric stretching in response to overburden. The average shape factor (T) in the Marcellus shale is oblate. The average T in the Woodford shale is prolate. Significant spatial variability of Previous HitmagneticNext Hit susceptibility is observed in both shales, suggesting a complex Previous HitmagneticTop mineralogy. An understanding of anomalous AMS fabric development in these shales units can provide insight into fluid flow processes.