Leak Detection Using Distributed Temperature Sensing: An Improved Calculation Method

This paper presents an efficient calculation to determine the transient heat transfer in ground surrounding a liquid pipeline. This improved calculation method was applied to support a feasibility assessment regarding implementation of Distributed Temperature Sensing (DTS) fibre optic systems for detection of leaks on an oil pipeline spanning long distances and varied geological conditions. With DTS, a leak or rupture could be detected if a portion of the sensor that is soaked is heated or cooled by leaked fluid. In many scenarios the temperature difference of a small leak may approach the sensing limits of the technology; calculating this limit requires an accurate understanding of the expected thermal characteristics of the fluid and soil surrounding the pipeline to identify where the technology is suitable and to calibrate accordingly. The method discussed in this paper was developed for use in heavy oil pipelines, for which changes in temperature have a large effect on the fluid viscosity, and therefore on frictional pressure losses. The model predicts the temperature profile in the soil surrounding a pipeline, including a number of transient effects. The model and results obtained are useful to identify optimal placement of a DTS cable, given a target size of detectable leak, time of year, and a number of parameters specific to the pipeline design. Importantly, this approach addresses changing geological conditions along the length of a pipeline, allowing an assessment of coverage and performance year round for the line under the most conservative case.