Well integrity management presents a wide variety of challenges for the industry today. With aging fields and more complex completion techniques coming into play, more efficient methods of well diagnostics and remediation are demanded. In the GOM, 45% of the wells have sustained casing pressure; therefore, the importance of having a resource that can provide an effective, accurate method of leak detection is abundantly clear.
Typical methods of leak detection today include the use of spinners, temperature tools and noise logs. Mechanical means such as calipers and isolation packers are also employed. While effective for larger leaks, these methods can produce nebulous results with smaller leaks and can be time consuming.
The frequency spectrum a leak produces is a function of differential pressure, leak magnitude, and leak geometry. These properties determine whether the frequency is audible, ultrasonic, or both. Typically, smaller volume leaks with a relatively high differential pressure will generate an ultrasonic signal. Based on this premise, an ultrasonic logging tool was developed and proven that detects frequency spectrums typically produced by leaks. The tool has a series of band pass filters which remove virtually all audible noise associated with tool movement, allowing continuous logging. Because ultrasonic energy will pass through compressed gas and steel, the tool can detect leaks in secondary barriers as well. Further, as ultrasonic energy attenuates quickly, the tool locates leaks with a high degree of accuracy. Using this tool, leaks as small as 0.005 gpm have been quickly located with an accuracy of a foot or less.
This paper will describe a down-hole ultrasonic leak detection tool and provide case histories of where the ultrasonic leak detection tool was used to find leaks that other methods were unable to locate. A comparison of the results from conventional leak detection methods will be discussed as well.