Resolution Enhancement of Sonic Logs Supported by Ultrasonic Data
- Jingxuan Liu (The University of Texas at Austin) | Ali Eghbali (The University of Texas at Austin) | Carlos Torres-Verdín (The University of Texas at Austin)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 60th Annual Logging Symposium, 15-19 June, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
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Sonic logs represent spatially averaged responses of rocks along the length of the receiver array. This measurement condition makes the interpretation of sonic logs across thinly laminated beds challenging.
We introduce a method to improve the vertical resolution of sonic logs by incorporating borehole images for better definition of small features such as thin beds or vugs. To that end, we develop an inversion-based interpretation method for sonic logs that uses high-resolution bed boundaries and compressional slowness obtained from ultrasonic borehole images. This method estimates high-resolution, layer-by-layer compressional and shear slownesses via joint inversion of compressional and shear slowness logs and ultrasonic-image-log-derived compressional slownesses.
To enable inversion-based interpretation, we use a new fast forward modeling algorithms for simulating sonic logs based on spatial sensitivity functions. The latter is combined with Backus averaging when bed thicknesses are smaller than the length of the receiver array to honor the long-wave equivalence requirements for a homogeneous anisotropic effective medium.
Two synthetic fluid substitution examples underline the importance of detecting laminations or other rock heterogeneities thinner than the length of the receiver array. Furthermore, the new-introduced inversion method is implemented to perform slowness inversion of field sonic log to construct earth models across highly heterogeneous laminated formations. Compared to conventional slowness data, high-resolution layer-by-layer slowness data exhibit wider variations on crossplots of Vp/Vs ratio and compressional slowness. For thinly laminated and highly heterogeneous formations, this inversion-based interpretation provides an improved estimation of rock-physics properties.
In formation evaluation, quantifying the petrophysical properties of thinly laminated or highly heterogeneous formations is essential for accurate reservoir characterization. Conventional processing of acoustic array waveforms provides an averaged sonic response over the length of the receiver array (typically 6 ft) by stacking the waveforms across the entire receiver array (Kimball and Marzetta, 1984). Beddings, laminated features or heterogeneities under the sonic resolution can be overlooked and commonly yield biased calculations of rock properties. (Peyret and Torres-Verdín, 2006; Oyler et al., 2008).
|File Size||2 MB||Number of Pages||11|