3D images of a wellbore generated in real time support drilling engineers to monitor wellbore profiles. Including the time as 4th dimension, 4D images can be used to analyze the evolution of the wellbore geometry as well as to support the drilling engineer in actuating appropriate counteractions in real time. Costly failures can be avoided more precise, alterations in the drilling practices to optimize the shape of the borehole will improve the drilling efficiency, or the driller is supported in making proper decisions such as reaming a critical zone or modifying the string rotation speed to reduce vibrations.

This paper reviews tests and experiments, which have been performed using high frequency ultrasonic caliper sensors in different drilling fluids and wellbore conditions. Test results show that with the new design of an ultrasonic caliper tool velocity of sound can be determined in real time at the pressure and temperature of downhole condition. This will increase the accuracy of the measured diameter and the shape of the borehole in real time.

In addition, a method for fast data transmission from down-hole to surface is presented and the best method for transmitting data to create the 4D images is discussed.

Even with such technology improvements the ultrasonic caliper cannot provide absolutely accurate information for all drilling environments and conditions. Several operational factors, such as mud density, borehole wall roughness, and tool position in the borehole need to be considered in order to optimize the accuracy of the borehole caliper data. For this reason, robust circle fitting algorithms based on the Kasa method have been implemented. In combination with the new design of the caliper tool, the accuracy of the results has been strongly increased.

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