外文翻译

OIL UNDER ICE DETECTION: WHAT IS THE STATE-OF-THE-ART?

Abstract. Since the exploration for oil and gas in the Canadian and US arctic

commenced in the early 1970s, a need has been identified to develop technology to

detect oil under ice. Both electromagnetic and acoustic sensors have been tried, but a

practical field instrument has not been identified. Most proposed systems require that

the equipment be operated from the ice surface in order to get adequate coupling and,

for some systems, the snow must be removed from the ice. For many ice situations,

surface access is difficult and poses a severe safety issue. Two recent spills in Alberta

used “high technology” ice augers to detect the presence of oil under the ice. Some

potential new techniques are discussed and the basic principles of their operation

described.

Keywords: arctic, oil spill response, oil in ice, detection

1. Introduction

The detection of oil under continuous ice cover has presented one of the most difficult

challenges to the oil-spill technological community for the past two decades and there

is still no operationally proven system available. Dickins (2000) under the

sponsorship of the US Minerals Management Service conducted an excellent

review of the status of oil-under-ice detection and this paper complements this review

with a more detailed analysis of some systems. Dickins identified many false start

concepts, which will not be discussed in this paper. In order to determine the design of

a suitable oil-under-ice detector, the various situations under which oil may be found

under a continuous ice sheet need to be considered.

The oil must come from a sub-surface release since any surface release would either

be on the ice surface or in a lead or other opening in the ice. Potential sources of

sub-surface oil are a leak in a pipeline, the leakage from a submerged tank or vessel or

a natural seep. Oil when trapped under ice does not spread rapidly or cover a large

area due to natural roughness of the ice-water interface (Rosenegger, 1975). The

situation is analogous to oil spilled on land, rather than the more dynamic situation of

oil on water. Unlike the oil-on-water situation, the probable location of the source of

the oil can be well defined spatially, so the search for the oil is over a relatively small

confined area. Depending on the time of year, the ice may just be forming, be in a

rapid growth phase, be essentially static or in a break-up situation, so that the oil may

be on the surface surrounded by ice floes, at the ice-water interface or in the sheet. In

the first and last case, traditional remote sensing techniques can be used to detect

the oil. When the oil is at the ice-water interface or incorporated in the ice sheet,

new oil-under-ice detection systems are required. The basic mode of detection may be

different for the two situations.

2. Existing Technology

The signal associated with the detection of oil under ice may be due to dielectric or

acoustic impedance difference between the oil and the ice, or by a change in the

surface roughness of the oil-ice interface. The rougher the interface, the more the

probing signal is scattered and hence the weaker the signal returned to the receiver. This is the basis, for example, of the detection of oil-on-water using radar. The

interface roughness has been directly measured using a mould system deployed by

divers (Goodman et al., 1987) and found to be rough at spatial scales of meters and

roughness values of several. The oil released under ice fills the roughness features and

generates a smooth inter the water, which can be detected using either acoustic or

electromagnetic sensors.

2.1. MECHANICAL SYSTEMS

The only proven and widely used technology is to drill a hole in the ice using an ice

auger, a chain saw or similar mechanical system. While this is time consuming and is

a single point measurement, it works. In order to increase the productivity of such

units, they can be mounted on a small snow vehicle to increase their coverage, but

consideration must be given to the additional safety concerns of using such equipment

on ice sheets of unknown thickness. Using hand-held systems, ice thicknesses greater

than about a meter and a half are difficult.

Some experiments (Dickins et al., 2005) have been conducted on the detection of the

vapour from the oil that would permeate through the ice and be trapped on the surface.

While this system worked well in the laboratory environment, it would be very

difficult to implement in a typical cold weather environment. This system is very time