Marine UXO (UneXploded Ordinance) Identification and Avoidance for a Shallow Water Pipeline Route
Authors: Halpin Sean Michael , Morrison Martin L. 
Published: July 2009

The oil and gas industry has long dealt with the challenge of UnExploded Ordnance (UXO) in terrestrial and marine environments. As the pace of offshore development continues to accelerate and as greenfield areas become fewer we are seeing expansion into areas that have experienced modern warfare. Modern munitions, unlike pre Cold War ordnance, are frequently comprised of non-ferrous materials, including non-ferrous (hence non-magnetic) metals such as aluminum, exotic alloys and uranium, plastics, and carbon fiber. Passive magnetics, normally used during conventional surveys, are unable to detect non-ferrous UXO and other commercially viable technologies must be explored for detection and characterization.

This paper addresses the commercial seabed and subseabed detection and location mapping of non-ferrous metallic UXO through the application of electromagnetic induction (EMI or EM) technology for shallow water marine pipelines.

Introduction:

Conventional pipeline engineering surveys collect high-density, high-resolution information to characterize the seabed and sub-seabed environment. Typical survey goals include: establish seafloor morphology, establish the seabed and subseabed soil properties and structure, and detect all objects that may prove hazardous to pipeline installation and operation. Survey data are collected by a variety of sensors: multibeam and sidescan sonars, magnetometers and subbottom profilers. In environments where UXO may be present, these sensors are normally sufficient to assess possible target density. However, in marine areas that have been subject to modern conflict, the presence of non-ferrous UXO, may go undetected using conventional survey technology and with the results drastically underestimating the number of potential UXO.

Shallow and ultra-shallow (less than 20m) marine environments present unique survey and pipeline installation challenges.

Environmental loading severity typically increases as water depth decreases due to the impact of wave energy on the pipeline and surrounding seafloor. Fishing pressure and the potential for interference from shipping traffic (e.g. anchors and dropped objects) tends to be considerably more intense in shallow water than in deep water. In northern latitudes, the formation, presence and movement of ice may contribute a significant loading factor. These environmental concerns must be addressed during concept development (e.g. requirements for pipeline protection) and survey design.

Potential UXO in shallow water must be given extra attention as there is a chance that the effects of on-bottom detonation may reach the ocean surface, possibly injuring or killing personnel and damaging assets. Given the extreme severity of the consequences of shallow water on-bottom detonation, every effort must be made to locate and effectively remediate the risk of UXO while keeping the cost of specialist surveys to a manageable level.

The successful completion of a UXO survey required rigid adherence to a process (Figure 1) including desktop study of potential UXO in the development area, design and testing of suitable survey systems, careful well documented field operations and then study of the data by persons experienced in the identification of munitions.