Marine Environment Unexploded Ordnance Assessment and Detection (EES)

The marine environment presents a complex challenge for unexploded ordnance risk mitigation - predominately caused by poor historical reporting


Marine Environment Unexploded Ordnance Assessment and Detection (EES)

Woodside Energy (NA) Ltd is Australia’s largest Oil & Gas Company and has a large exploration and production portfolio in Africa. In September 2006, Woodside Energy (NA) Ltd, as part of their due diligence and Health and Safety Policy commissioned RPS Explosives Engineering Team (EET) to conduct an historical desktop study for potential Explosive Remnants of War (ERW) and bulk munitions contamination within the Concession Areas 35, 36, 52 and 53, which are situated in the Gulf of Sirte off the Libyan coast.

BACKGROUND

Information was obtained from various establishments, source locations and archives, which highlighted the potential risk within the allotted concession areas. There was no intrusive or non-intrusive survey data was available during the compilation of the desk study. All the information gathered was based on historical information obtained from a number of sources.

The research conducted identified that over 60 known shipwrecks from World War Two were sunk and the German & Italian forces laid over 3000 sea mines in the Gulf of Sirte. Furthermore to the north west of concession area 35 Explosives Dumping Grounds were identified. Based on this information the sources of contamination were established and the items listed below identified as potentially being present within the concession and as such could pose a risk during drilling operations:

·        Sea mines, depth charges and torpedoes

·        Air delivered bombs and rockets

·        Munitions cleared from land and dumped out at sea

·        Munitions on wrecks from attacking aircraft, ships and coastal artillery

·        Munitions from the holds of wrecks broken up by the sea and weather

Given this potential risk, RPS EET recommended that the following risk mitigation measures be implemented:

·        Explosives Safety Briefing for all operational personnel

·        Marine Explosives Engineer support during the intrusive operation phases

Woodside planned to conduct exploratory drilling at eight sites throughout their granted concession areas using Atwood Hunter a Semi Submersible Mobile Offshore Drilling Unit (MODU). The unit deploys eight anchors to keep on station; it does not however lower legs to the seabed. Therefore the only potential risks were assessed to be from the anchor deployment/recovery and the initial stages of drilling when the head unit comes into contact with the first layers of the seabed.

DEPLOYMENT

RPS Marine Explosives Engineers (MEE) deployed out to Malta to join MODU Atwood Hunter to give support during the positioning for the first drill location in concession area 35. The first task was the laying of the eight anchors, this is conducted with the use of Anchor Handling Vessels (AHV) Battler & Laborde and took 40 hours to complete.

Following successful positioning the next phase is the “pre spudding” survey, which involves a Remote Operated Vehicle (ROV) conducting a 360º visual and sonar sweep of the intended drill site. This is always completed regardless of any suspected UXO that could be present. An MEE was present to monitor this operation. Due to the potential shallow gas risk in the intended drill location a pilot hole would need to be drilled first, this was to be 80m away from the intended drill site. Again, an ROV survey was carried out prior to this taking place. The final “spudding” was completed on 14th April 2007. No items of UXO were snagged or observed during any of the supported operations and the MEE’s departed Atwood Hunter to Misratah in Libya.

Contact Dave Denman

00441291621821

denmand@rpsgroup.com
 

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