Pulse-echo ultrasonic measurement techniques are used in the oil and gas industry for imaging casings and tubings for cement bond and corrosion evaluation. Conventional downhole ultrasonic measurement tools typically consist of one or multiple ultrasonic transducers, that probes inner surface and are rotated to provide full azimuthal coverage. This paper proposes a method of achieving this using phased array transducers.

Phased array pulse-echo methods are widely used in non-destructive testing and medical applications. In a typical operation, multiple elements are activated in collaborative fashion to transmit and receive the ultrasonic waves. By introducing de-phasing among the elements, the ultrasonic beam can be shaped and directed onto regions of interest to target. The main advantage of this technique for cased hole imaging is the versatility thanks to a high number of emitting and receiving elements that are placed around the circumference of the tool; electronic scanning can replace the mechanical rotation that requires complex mechanical systems.

SLB has developed such a phased array ultrasonic transducer integrated into an experimental prototype tool and conducted logging in test cells at the NORCE Norwegian Research Centre facility. The test cells are made of a variety of pipes with designed cementing defects. In this paper, we will introduce an overview of downhole phased array measurements and present test cell logs in comparison to the reference logs from commercial tools. The results show a good agreement between images obtained from the legacy and new phased array sensors in the tested conditions.

This paper reports one of the first well integrity measurements performed with an ultrasonic phased array for azimuthal cement bond and pipe thickness imaging. On the other hand, the simplification of the tool architecture allows a reduction of the outer diameter and unlocks the possibility to deploy such a tool on monocable in diameters starting from 3.5 in. casing/tubing, which was not available before.