Geophysical Approach to Submarine Pipeline Surveys
Authors: Van Reenan Earl D. 
Published: October 2008

A number of geophysical methods and survey devices are available for conducting comprehensive studies of submarine pipeline routes. The primary objectives of these studies are to determine water depths, sediment characteristics, depth or presence of bedrock, bottom debris, existing currents and precise locations of existing pipelines.

Hydrography, high-resolution seismic profiling, sonar side s canning, magnetic measurements, and sediment sampling can all be carried out from a single ship operation to meet the objectives of the route survey. The side scan sonar can also be used to locate or monitor existing pipelines and is particularly effective for rapidly locating exposed areas of pipelines in river crossings to pinpoint potential trouble areas for remedial work.

The costs for carrying out these studies are minimal when measured against the value of avoiding costly installation problems or submarine pipeline repairs.

INTRODUCTION

Many factors must be considered when designing and planning a submarine pipeline. After the required pipe diameter is established, the specific gravity of the pipeline must be balanced against lift and drag forces from currents and possible storm surges. The water depth and type of s oils encountered must be considered along with the necessity to bury the pipe in some areas to avoid anchor snags, bridging, or shifting. When a route is selected, that route should be surveyed and studied to collect as much data as possible concerning the hydrography, soil characteristics, presence of obstacles and location of existing pipelines, current velocity data and other pertinent information.

The purpose of this paper is to outline a comprehensive survey approach to marine pipeline route studies. The tools and techniques to accomplish these studies can be provided from a, single ship operation if proper planning and coordination are used. Figure 1 illustrates the concept of using several sensors and sonic devices simultaneously from the survey ship. The following devices are used for these studies:High-resolution seismic profilerPrecision depth sounderSide scan sonarMarine proton magnetometerBottom sediment samplersCurrent meters

The following sections describe these devices and their use for obtaining pertinent data for submarine pipeline route investigations.

2. EQUIPMENT

The electronic sensing instruments and mechanical sampling devices used for these studies consist of commercially available equipment. Some of these systems require considerable skill and experience to operate at optimum effectiveness. The success of these projects is directly proportional to the operators I skills as well as to proper supervision and coordination. Therefore it is advisable to use well-trained professional personnel on these projects to assure successful operations.

2.1 Seismic Profiling

A number of systems are commercially available for obtaining seismic profiles; however, many of these devices have limitations. The ideal systems combine high resolution of near-surface sediment data along with relatively deep penetration capabilities. Consistently effective devices for this application have been the electro-mechanical system?s such as one produced by EPC Labs. This system produces a short, clean sound impulse with a minim um of secondary cavitation or ringing.