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This article describes the advances in tool design and resulting data quality of the Sonic Scanner tool. Examples from the USA, Norway and Mexico highlight applications that include determining formations,


for


shear velocities in ultraslow radial profiling


drilling, completion and sampling operations, fluid-mobility logging, fracture characterization and imaging away from the borehole.


Engineering Success More so than electromagnetic and nuclear logging tools, a sonic tool’s very presence in a borehole can introduce a bias to the measurements it acquires. The steel tool housing is extremely efficient at propagating sonic waves. Sonic-logging tool designers have minimized this unwanted effect by isolating the transmitters from the receivers with insulating materials or by milling slots and grooves into the steel sonde (see “ History of Wireline Sonic Logging,” page 32). These efforts were aimed at delaying undesirable signals and making the tool as transparent to the measurement as possible. The Sonic Scanner tool is completely


different from other tools. Its design, material composition and components were engineered so that the effects of its presence could be modeled. These effects can then be incorporated into predicting the complete tool-borehole-formation response. These theoretical predictions have been verified by experimental results in a test well having known formation properties. As a result, tool effects can be predicted accurately in isotropic homogeneous formations, and real-time corrections can be made at the wellsite. The transmitter-receiver (TR) geometry and functionality of the new tool were carefully designed to provide P-, S-, Stoneley- and flexural- wave slowness measurements at varying radial depths of investigation (for a review see “ Borehole Acoustic Waves,” page 34). These modes are acquired at a logging speed of 1,800 ft/h


[ 5 49 m/h] . For the typical scenario with formation compressional and shear speeds increasing with distance from the borehole, this is achieved by increasing TR spacing to probe deeper into the formation. The Sonic Scanner tool combines this long-spaced approach with the close TR spacing of a borehole-compensated arrangement, and also adds azimuthally distributed receivers. The tool features 13 axial stations in a 6-ft [ 1.8-m] receiver array. Each station has eight receivers placed every 45 ° around the tool, for a total of 104 sensors


optimizing


Spring 2006


15


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