The Development and Operations of a Depth of Buria Survey System To Meet the Requirements of H.R. Bill No. 4888
Authors: Swinney E.A. 
Published: October 2008

The paper will review the development and operation of a first generation shallow water pipeline depth of burial survey system. The system is designed to meet the requirements of PL101–599. The emphasis of the paper sill not e on the actual pipe detection sensor itself but rather the ancillary techniques and techniques and technologies which developed along the way. From being a simple single sensor array, the system developed into a multi sensor complex system. The developments cover the areas of pipeline identification, seafloor definition and sensor array motion. The problems created by these topics will be illustrated and the solutions described and evaluated.

THE DEVELOPMENT

As it became apparent that pipeline depth of cover surveys would become a requirement, the authors division within the company was tasked with the development and operation of a system. At this stage no "off the shelf!? system was available and depth of cover of pipeline was not a feature that was often requested. To develop an operational system the department set itself the following constraints.The system had to be operational within one year. This meant using as much existing technology as possible.The system had to meet the (then) expected legal requirements.The system had to minimize capital investment. The repeat surveys may be as much as five years apart and given that time frame, system obsolescence is apossibility, therefore recovery of investment must be achievable in the first round of surveys.The system must operate in all of the conditions found in the Gulf of Mexico which came under the law.The system must be commercially attractive, both technically and financially.

At the time the constraints Were set there was only one known way of determining the depth of cover over a pipeline in shal1ow water and this entailed utilizing divers who would physically probe for this line. This method was taken as the baseline both technically and commercially. Any improvement which could be made would indicate probable success for the system.

The conclusion reached was that the diver probe method was sometimes inaccurate, especially where indeterminate seabeds occurred and it was extremely slow and expensive.

The seabed in the Gulf of Mexico varies from hard shell areas to extremely soft silts. In the extremely soft areas a diver cannot define the seabed water interface to any degree of accuracy. Acoustic systems will also provide differing results depending upon the frequency used. A higher frequency generally reflecting from a shallow horizon while the lower the frequency the deeper the reflector.

The prime technical objective was to design, develop or obtain the sensor which could determine position and depth of a pipeline. The authors division within the company was also responsible for pipeline surveys in deeper water utilizing Remotely Operated Vehicles (ROV'S). During many surveys the Innovatum pipe tracking system had been utilized and thus it was intuitively felt that a system built around Innovatum may succeed.