Investigating the integrity of a casing, with the tubing in place, has always presented a challenge to operators worldwide. Even more challenging, is taking on an investigation into cross flow between formations & identifying regions of flow behind pipe, all while the tubing is still in place.
Flow behind pipe has always been a well debated subject amongst industry professionals; most advancement in this matter has been subjective, based on well educated speculation and largely dependent on temperature profiles and changes in the geothermal gradient. Saudi Aramco have recently utilized a new ultrasonic based, diagnostic technology, in order to map regimes of flow behind pipe, identify cross flow between downhole formations, locate casing leaks with a pin-point accuracy, all while the tubing is in place, and while using conventional Electric Line logging.
This technology exploits the innate physical properties of ultrasound. The capacity of ultrasonic waves to propagate through numerous and varied media, including steel, liquids & compressed gas; allows a radial investigation of up to 3m. Unlike several technologies that utilize ultrasound, this diagnostic tool, is a passive listener, with no transmitters. It is designed to pick up the sonic energy fluctuations created by the turbulent flow of fluids over a specific spectrum within the ultrasound frequencies window. A window that is so uniquely suited for precision wellbore diagnostics.
This paper presents the basic physics behind the technology chosen by Saudi Aramco to address the aforementioned issues. It will highlight the possible applications of these tools and more specifically discuss the recent case studies successfully performed in Saudi Aramco.