Influence of borehole-eccentred tools on wireline and logging-while-drilling sonic logging measurements

Abstract
We describe a numerical study to quantify the influence of tool-eccentricity on wireline (WL) and logging-while-drilling (LWD) sonic logging measurements. Simulations are performed with a height-polynomial-adaptive (hp) Fourier finite-element method that delivers highly accurate solutions of linear visco-elasto-acoustic problems in the frequency domain. The analysis focuses on WL instruments equipped with monopole or dipole sources and LWD instruments with monopole excitation. Analysis of the main propagation modes obtained from frequency dispersion curves indicates that the additional high-order modes arising as a result of borehole-eccentricity interfere with the main modes (i.e., Stoneley, pseudo-Rayleigh and flexural). This often modifies (decreases) the estimation of shear and compressional formation velocities, which should be corrected (increased) to account for borehole-eccentricity effects. Undesired interferences between different modes can occur at different frequencies depending upon the properties of the formation and fluid annulus size, which may difficult the estimation of the formation velocities. © 2013 European Association of Geoscientists & Engineers.

Citation
Pardo, D., Matuszyk, P. J., Torres-Verdin, C., Mora, A., Muga, I., & Calo, V. M. (2013). Influence of borehole-eccentred tools on wireline and logging-while-drilling sonic logging measurements. Geophysical Prospecting, 61, 268–283. doi:10.1111/1365-2478.12022

Acknowledgements
The work reported in this paper was funded by the University of Texas at Austin Research Consortium on Formation Evaluation, jointly sponsored by Anadarko, Aramco, Baker-Hughes, BG, BHP Billiton, BP, Chevron, ConocoPhillips, ENI, ExxonMobil, Halliburton, Hess, Marathon, Mexican Institute for Petroleum, Nexen, Pathfinder, Petrobras, Repsol-YPF, RWE, Schlumberger, Statoil, Total and Weatherford. The first author was partially funded by the Spanish Ministry of Sciences and Innovation under project MTM2010-16511, the Laboratory of Mathematics (UFI 11/52) and the Ibero-American Project CYTED 2011 (P711RT0278).

Publisher
Wiley

Journal
Geophysical Prospecting

DOI
10.1111/1365-2478.12022

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