Standoff and Caliper Measurements While Drilling Using a New Formation-Evaluation Tool With Three Ultrasonic Transducers

Abstract

Abstract A new formation-evaluation LWD tool that employs three ultrasonic transducers to determine tool standoff and borehole diameter is presented. The ultrasonic data are used to improve density and neutron-porosity measurements obtained from the same tool. The paper describes the ultrasonic transducer hardware and operating characteristics, as well as a unique technique for setting the ultrasonic threshold. Data processing procedures and caliper equations are also presented. Downhole phenomena that adversely affect the measurements are discussed, along with solutions used to handle them. Log examples illustrate the effectiveness of the ultrasonic measurements and include evidence of sticking, lateral bouncing, and whirling of the toolstring while drilling. Although monitoring of these undesirable bit motions is not currently available, future tools will be able to communicate this information to the surface to aid drillers.