HYDRO 2016 Paper 6A3

Burial depth determination of cables using acoustics – Requirements, issues and strategies

Jens Wunderlich, Jan Arvid Ingulfsen, Sabine Müller

In the oil/gas business surveys to obtain the depth-of-burial (DOB) of pipelines and cables are done on a regular basis. DOB surveys shall determine the exact position and burial depth of the pipeline or cable directly after dredging and later in regular intervals during it's entire lifetime. With expanding offshore wind farming in the wake of the "Energiewende", site explorations, route and cable DOB surveys become increasingly important in this offshore sector, too.

Various geophysical methods like magnetic, electromagnetic and acoustic sensors are used to detect and track buried cables. This paper will consider acoustic technologies only.

For best detection probability of buried cables to date often lines crossing the expected cable route are surveyed. Although this is a good method to detect the cable and get its position, survey companies require more efficient technologies, accounting for both, operational and processing costs. Thus they are looking for easy to operate technologies that follow the cable along its actual route, work at different water depths, weather and seabed conditions and give immediate and reliable results to produce deliverables with high accuracy of XYZ cable positions. Following the cable requires a sufficient survey corridor and real-time cable tracking to avoid the cable falling out of this corridor. Different cable properties like diameter, shape and material, the survey-vehicle's speed and environmental conditions like noise level, weather and type of seabed have to be taken into account.

This paper summarizes user requirements for DOB surveys, identifies limitations of currently used acoustic technologies and discusses different approaches to overcome these issues. Application of the methods shown is not limited to cable DOB surveys, they may also be used for pipeline surveys or other activities during construction and maintenance of offshore structures, e.g. to detect boulders, UXO or other debris during site and route surveys.