Dictionary:Dipole sonic log

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A sonic array tool in which sources are dipoles as opposed to radially symmetric monopoles, so that it generates both P- and S-waves in formations. Analysis involves mode identification and analysis of dispersion curves and yields both P- and S-wave velocities. A variant (crossed dipole mode) is an orthogonal set of horizontal dipole transmitters and an array of orthogonal dipole receivers to measure azimuthal anisotropy. This arrangement is suitable for detecting azimuthal velocity variations in a borehole. The dipole sonic imager (DSI) is a multiconfigurable tool that can emulate a BHC sonic, a standard monopole array tool, or an array dipole tool. Modes are configured to meet the logging conditions presented by different borehole environments. While monopoles work well in hard formations where mode conversion is required for S-wave recording, dipoles excite flexural modes directly and are efficient for generating Stoneley waves in slow formations. The analysis of the proper dispersion curves (modes) leads to the estimation of S-wave velocities in slow formations. Dipoles are directional and are sensitive to azimuthal velocity variations.