Estimating A Shear Modulus Of A Transversely Isotropic Formation
Name
1990.2 Ellefsen et al.pdf
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657.81 KB
Format
Adobe PDF
Checksum (MD5)
264b32e997f616530c183ea01c4af426
Author(s)
Ellefsen, K. J.
Cheng, C. H.
Toksoz, M. N.
Date Issued
1990
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1990-02
Abstract
A method to estimate c[subscript 66], which is a shear modulus of a transversely isotropic formation (with its symmetry axis parallel to the borehole), is developed and tested. The inversion for c[subscript 66] is based upon a cost function which has three terms: a measure of the misfit between the observed and predicted wavenumbers, a measure of the misfit between the current estimate for c[subscript 66] and the initial guess of its value, and penalty functions which constrain the estimate for c[subscript 66] to physically acceptable values. The inversion is applied to synthetic data for fast and slow formations, and the estimates for c[subscript 66] are within 5% of their correct values and are well resolved. The inversion is applied to field data from a formation which consists mostly of siltstone. All estimates for c[subscript 66] are significantly higher than for c[subscript 44] , and the S-wave anisotropy generally ranges from 19 to 24%.
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