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Second EAGE Workshop on Borehole Geophysics
- Conference date: 21 Apr 2013 - 24 Apr 2013
- Location: St Julian's , Malta
- ISBN: 978-90-73834-46-0
- Published: 21 April 2013
41 - 42 of 42 results
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An Amplitude Scaling Methodology for 2D/3D Migrated VSP Data
Authors M. Lou, J. Meng, D. Cheng and F. DohertyVSP data can provide a significantly high resolution image. However, VSP data is characterized by a highly uneven distribution of both CDP fold and reflection incident angles laterally away from the borehole. One end effect of this uneven distribution is a migration image characterized by amplitude decay as a function of offset from borehole in migrated VSP data. This paper presents an amplitude scaling methodology to compensate the offset-dependent amplitude decay. We first locate a geologically stable and flat event above a target zone, and calculate its RMS amplitude distribution as a function of offset. From calculated RMS amplitudes we then characterize the amplitude-decay pattern by least-squares fitting. While each dataset may be analysed by various polynomial or Gaussian functions for best fit, this paper we suggest the amplitude-decay pattern can be characterized by a four-term Gaussian function. Finally, by reversing the best fit function, an amplitude scaling factor is applied to each trace of the migrated VSP data. We demonstrate the methodology greatly enhances the dimming amplitudes at long offsets in migrated VSP data. The amplitude distribution of migrated events after scaling is laterally more homogenous, potentially allowing the data to be used for lithological inversion and interpretation.
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Transmission Amplitude Variation with Offset (TAVO)
Authors A.A. Al-Shuhail and A.K. PopoolaThis study presents new approximations for the transmission PP and PS coefficients from Zoeppritz equations. The approximations are presented in a form that is convenient for conventional AVO analysis. The expressions are tested using several reservoir models by comparing their performance to their corresponding Zoeppritz expressions. Results show that a one-term approximation is good at small to intermediate incidence angles while two or three terms might be required at large incidence angles approaching the critical angle. We show also that using higher number of terms does not improve the results. The presented approximations are ideal for use with VSP geometry and offer several advantages over existing reflected AVO analysis.
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