Hole size measurements while drilling are difficult to make because the dynamic environment precludes the use of a truly mechanical device. Several MWD caliper tools, which utilize acoustic technology, are available to the industry but they typically have a limited operating range and are often integrated with other MWD sensors, such as a density or sonic tool.1,2,4 

Technical issues which could preclude the use of acoustics for an MWD caliper tool include the noise associated with the downhole drilling environment, tool accuracy, tool reliability, and errors associated with mud attenuation and signal detection, tool eccentering, formation cuttings, gas, etc.

This paper describes the design and testing of a new MWD acoustic caliper tool. The tool has been designed with its own processor, memory, power supply, and surface communications port, so it can be run in a standalone mode or integrated with other MWD sensors. This new sensor utilizes new digital signal processing technology, which increases its accuracy and operating range, when compared to previous MWD acoustic caliper tools.

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