Development of a downhole ultrasonic transducer for imaging while drilling

A novel development process was used to design, fabricate, qualify, and test a downhole ultrasonic transducer to acquire a high-resolution borehole surface image in the harsh environmental operating conditions experienced while drilling. The ultrasonic transducer was designed and developed to be incorporated into a downhole drilling tool to acquire a pulse-echo signal from the borehole wall, known in the industry as imaging while drilling. The design of the transducer incorporated acoustic modeling to achieve the desired sensitivity and bandwidth using a composite piezoelectric element, two impedance matching layers, and a high impedance backing. Mechanical design techniques, including a manufacturing procedure that produces reliable bonds between layers, a ruggedized housing, and impact-resistant transducer packaging, were chosen to ensure the transducer's reliability in the downhole environment. A standard pulse-echo transducer test procedure was created to acquire accurate, repeatable measurements for quality control and performance monitoring. Environmental qualification testing was conducted on a prototype transducer to validate the transducer's functionality during exposure to vibration, temperature cycling, and high temperature and pressure. Successful field tests of an imaging while drilling tool with the new borehole imaging transducer have verified the transducer has sufficient sensitivity and bandwidth to reliably acquire a high-resolution borehole image in the downhole drilling environment.