Precise inversion of logged slownesses for elastic parameters in a gas shale formation
Author(s)Miller, Douglas E.; Horne, Steve A.; Walsh, John
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Dipole sonic log data recorded in a vertical pilot well and the associated production well are analyzed over a 200×1100-ft section of a North American gas shale formation. The combination of these two wells enables angular sampling in the vertical direction and over a range of inclination angles from 54° to 90°. Dipole sonic logs from these wells show that the formation's average properties are, to a very good approximation, explained by a transversely isotropic medium with a vertical symmetry axis and with elastic parameters satisfying C[subscript 13]=C[subscript 12], but inconsistent with the additional ANNIE relation (C[subscript 13]=C[subscript 33]−2C[subscript 55]). More importantly, these data clearly show that, at least for fast anisotropic formations such as this gas shale, sonic logs measure group slownesses for propagation with the group angle equal to the borehole inclination angle. Conversely, the data are inconsistent with an interpretation that they measure phase slownesses for propagation with the phase angle equal to the borehole inclination angle.
DepartmentMassachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Society of Exploration Geophysicists
Miller, Douglas E., Steve A. Horne, and John Walsh. “Precise Inversion of Logged Slownesses for Elastic Parameters in a Gas Shale Formation.” Geophysics 77.4 (2012): B197. ©2012 Society of Exploration Geophysicists
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