Spotting those spills
  from: Offshore Engineer
  by: Terry Knott
  Wednesday, May 11, 2005

Detecting the release of oil to the sea from offshore installations or ships on a continuous basis is no easy task. But now a new technique has emerged that promises to identify and report oil spills as they occur, as Terry Knott reports.

'While preventative measures have been taken worldwide to reduce oil being released into the marine environment,' says Casper Kvitzau of online environmental surveillance specialist OSIS International in Denmark, 'it is estimated that more than 500,000t of oil are spilled into the sea every year. But success in identifying the precise sources of the oil spills is not that great.'

By way of example, he points to the 'Special Areas' designated by the United Nations' International Maritime Organisation (IMO) under Annex 1 to the Marpol 73/78 protocol, to protect sensitive marine environments from ship discharges - the protocol has so far been ratified for the Mediterranean, Black Sea, Red Sea, Gulf of Oman, Gulf of Aden, the Arabian Gulf region, Antarctic, Baltic and northwest European waters. While the Marpol protocol does not specifically cover offshore structures, national and regional regulations, for example the Ospar Convention covering the North East Atlantic, do focus on discharges from the offshore industry.

'The present strategy for detecting oil pollution in sensitive areas relies heavily on aerial surveillance,' he notes. 'The local authorities make regular surveillance flights but their resources are very stretched, so they tend to focus on, say, just the main shipping lanes. Or they may purchase satellite images, but these are really snapshots in time, not round the clock, and don't always prove who discharged the oil. With thousands of ship movements and hundreds of offshore platforms in these regions, aerial surveillance cannot hope to spot all releases of oil. Offenders are rarely caught in the act and brought to prosecution.'

In a report published in 2002 by the National Research Council of the US National Academy of Sciences, the average total worldwide annual release of oil from all known sources to the sea was estimated at 1.3 million tonnes - arising from a wide range, possibly 470,000t to 8.4 million tonnes per year. According to the report, while natural oil seeps accounted for 46% of the oil, among the other principal sources, operational discharges from ships and discharges from land-based sources produced 37%, accidental spills from ships 12%, and 'extraction of oil' - the offshore industry - only 3%.

While the offshore industry might take some comfort in its relatively small contribution to the overall problem, Kvitzau points out that offshore platforms are currently exempt from the Special Areas protocol, which requires oil discharge levels to be below 15ppm for vessels under 400t, and no discharges from larger vessels. Under Ospar, the current requirement for platform discharges is 40ppm, with a recommendation that this be reduced to 30ppm in 2006.

'Ospar produced an action plan in the late 1990s which called for the development of best available techniques and best environmental practices for the control of oil and other substances in aqueous discharges from offshore installations,' says Kvitzau. 'The drive is toward harmonising the IMO and Ospar regulations so that platforms will also be more restricted in the discharge of oil. This will require more effective monitoring of oil emissions from offshore structures,' he observes.

Driven by the need for better surveillance, the OSIS project was set in motion five years ago to develop and demonstrate a sensor system, mounted directly on offshore platforms that would perform 24-hour surveillance in checking for oil spills. The prototype of that system has recently completed offshore trials.

Funded by the Danish Environmental Protection Agency, Danish Energy Authority and the European Union, the development by OSIS International of OSIS - oil spill identification sensor - has been targeted at delivering a system which can detect oil spills round the clock, estimate the area of a spill and its thickness, and relay this information to onshore authorities in real time.

The prototype platform-mounted sensor at the heart of the system is packaged in a fibre glass and aluminum pod, and is driven by an electric motor so that it rotates to sweep the area around the installation - the prototype is 1.65m high and 1.5m in diameter, weighing 460kg, although a commercial version would be smaller, says the company.

Contained within the unit are two primary sensing systems. One is radar, which, with the help of rule-based pattern recognition software built into the device, can detect the presence of an oil spill on the surface of the sea. The detection range stretches over several kilometers and the system calculates the area of the spill.

The second sensor is a microwave radiometer. This measures 'brightness temperature', a measure of the intensity of radiation thermally emitted by an object.

'Bodies such as water or oil emit microwave radiation,' explains Jesper Holst, technical manager for OSIS International. 'Furthermore all bodies reflect and absorb a portion of the equivalent microwave radiation from other bodies in the area. In this case those other bodies may be clouds or ships, for example. In addition, microwave radiation from space also strikes the bodies and is reflected. The OSIS sensor detects all of these very small and complex signals and makes allowance for them in the analysis algorithm. OSIS can not only distinguish between oil and water from their relative brightness temperatures, but sophisticated software algorithms can also provide a measure of the thickness of the oil, from 0.2mm to 2mm thick.'

Data collected by the OSIS sensor pack is analysed in a master unit located offshore and transmitted via satellite to a central server onshore, which can collect data from sensors at multiple sites around the world - data transmission costs are kept down by only sending information if an oil spill occurs. Automated decision-making software in the central server converts the sensor data into oil spill information, displaying the result graphically on the users' computer screens, for example within regulatory bodies and offshore operating companies.

'Users registered on the OSIS central server will have access to predefined surveillance areas, displayed on the OSIS viewer,' explains Kvitzau, co-ordinator of the project for OSIS International. 'The viewer (see illustrations) enables the user to navigate easily between a general overview of the surveillance area and the specific readings of the selected sensor. In the case of an oil spill, the system provides the user with spill location, distances and oil volume estimates, which will help plan cleanup operations.'

One scenario for offshore applications envisages sensor packs located on several platforms in a region transmitting data by wireless ethernet to a local master unit, which then links to the satellite and central server.

The master unit enables up to 16 sensor packs to communicate through a single satellite channel.

The OSIS prototype was built in 2003, and has since been certified by DNV for offshore and marine applications, with patents pending in the US and Europe. In collaboration with the Danish navy in 2003, OSIS was used in a trial to detect a rape seed oil spill at the naval harbour at Korsør in Denmark, and subsequently calibrated onshore in the first quarter of 2004. An offshore test programme began in May 2004 for which OSIS was initially mounted onboard the Danish environmental vessel Gunnar Seidenfaden, again detecting spills of rape seed oil, trials which yielded important data for optimising the software algorithms. The sensor was then moved to jackup rig Ensco 70, drilling under contract with operator DONG on the Nini and Sofie fields in the Danish sector. The trials, which concluded in March this year, are reported to have been very successful, providing the data needed to finalise the design of a commercial sensor pack.

'OSIS demonstrated it could provide 24 hour surveillance and maintain its accuracy in wind speeds up to 15m/s and wave heights around 10m,' says Kvitzau. 'Oil spill thickness was accurately detected up to 1.5mm, but we can take this further by applying different frequency bands in the radiometer - the prototype has only one frequency band. But even having a measurement up to 1.5mm gives you an idea of the minimum amount of oil you would have to deal with in a spill cleanup.'

Fitted to a vessel, OSIS could also be used in 'forward looking' mode in cleanup operations.

The company believes that once the surveillance technique is established, its inclusion on a platform could help lower insurance costs for the operator, and in future, operators having a 'positive environmental profile' resulting from the routine use of OSIS might influence their selection for exploration in sensitive marine areas.

OSIS International is now beginning work on a version of the system tailored for use on ships. In these applications, OSIS will be designed to interface with the Universal Automatic Identification Systems (UAIS), required by the IMO to be fitted to all vessels over 300t from the end of 2004 to help track vessels by satellite and avoid collisions.

In operation, OSIS would normally transmit an 'all clear' signal along with the regular UAIS transmission. Should an oil spill be observed by OSIS, the data will automatically be sent via satellite to the central server onshore, as in the case of offshore installations. OE

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