Untangling Acoustic Anisotropy
- Jennifer Market (Weatherford) | Camilo Mejia (Weatherford) | Ovunc Mutlu (formerly Weatherford) | Mojtaba P. Shahri (Weatherford) | Joanne Tudge (Weatherford)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- October 2015
- Document Type
- Journal Paper
- 420 - 439
- 2015. Society of Petrophysicists & Well Log Analysts
- 1 in the last 30 days
- 275 since 2007
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Acoustic anisotropy analysis is used in a wide variety of applications, such as fracture characterization, wellbore stability, production enhancement, and geosteering. However, acoustic anisotropy methods are not always understood clearly, both by the end user and the data analyst. Azimuthal variations in velocities may be due to stress variations, intrinsic anisotropy, bed boundaries, or some combination thereof. Environmental effects, such as hole inclination, centralization, wellbore condition, dispersion and source/receiver matching, affect the viability of the data to detect anisotropy and must be considered in the interpretation. Untangling the various acoustic anisotropy types from environmental effects is essential to interpret the results correctly.
This paper begins with a discussion of the types of acoustic anisotropy, followed by a review of common industry methods for extracting anisotropy from wireline and LWD azimuthal sonic data. Environmental factors such as tool centralization, irregular borehole shape, poor tool calibration, and dispersion are considered, paying particular attention to the practical limitations of acquiring data suitable for high-quality anisotropy analysis in adverse conditions.
Quality control techniques are discussed in some detail, as they help identify various causes of “false anisotropy” due to processing artifacts. Quality control plots, such as shear slowness images, dispersion crossover plots, and combined analysis with calliper and microimages, are suggested to aid the nonspecialist in determining whether the anisotropy results are viable.
Intrinsic, induced, and geometric anisotropy are discussed in detail, along with consideration of the depth of sensitivity of acoustic measurements. A case study is presented to illustrate the art of untangling overlapping acoustic anisotropy responses.
|File Size||19 MB||Number of Pages||20|