CASE STUDY: PIPELINE OBSTRUCTION

Client: BP Exploration
Project: Subsea pipeline
Task: Obstruction location

Raw_filtered_data_whitebg

Figure 2: Effect of filtering the acoustic signal. Upper graph shows the original measured signal and the lower graph shows this signal after it has been passed through an ultra-narrow band filter.

Excavation of the pipeline after these tests identified the obstruction in the precise location determined by Acoustek®.

Here Acoustek® was used to locate an obstruction in a pipeline. In this particular study, it was necessary to use Acoustek® because parts of the pipeline were buried in a rock dump, meaning access to the pipeline was restricted, such that no alternative techniques could be used to survey the pipeline with the detail required. In this study, the field was still producing at the time of the survey and there was considerable background noise.

The upper graph in Figure 2 shows the signal recorded by the microphone for one acoustic pulse test. The high levels of noise in this signal make it very difficult to identify any subtle reflections emanating from the obstruction in the pipeline. The lower graph in Figure 2, however, shows the response after it has been filtered using digital filter technology. This filter is able to reject the high and low frequency noise that is present in the signal and enables the reflections from an obstruction located approximately 450 m away from the platform to be clearly identified. 1st, 2nd and 3rd reflections can be seen from the obstruction as the acoustic signal passes back and forth between the platform and obstruction. Excavation of the pipeline after these tests identified the obstruction in the precise location determined by Acoustek®.