June 03, 2020

UK multinational chemicals company Ineos advised that the UK Offshore Pertroleum Regulator has approved the decommissioning plans for the Cavendish Field located approximately 125km east of the UK coastline at Flamborough Head and 65km west of the UK-Netherlands median line, with a water depth of 18 metres. The Cavendish NUI is tied back to the Murdoch MD platform, 44km to the south-east. The Cavendish NUI comprises a piled steel jacket supporting topsides of five decks, plus a helideck. A facilities building extends over two decks. The topsides weighs 546 tons and the jacket weighs 508 tons. Produced gas and condensate, from three wells, at Cavendish was exported via a 47.35km long 10.75” export pipeline, to Murdoch. A 2.37” methanol line is piggybacked onto the 10.75” export pipeline which supplied methanol from the Murdoch platform back to Cavendish. A 1.25” fibre optic cable is also laid in the same trench as the pipeline bundle.
Cavendish production ceased in August 2018 due to the closure of the export route to shore via Murdoch. The two pipelines are out of use and reside in a cleaned, water-filled condition.
The decommissioning activities are summarised as follows.
– Wells have been plugged and abandoned in accordance with Oil & Gas UK guidelines;
– Topsides and jacket will be removed and recycled or disposed of onshore;
– The gas export pipeline, piggybacked methanol line and fibre optic cable will be partially removed. – The tie-in spools will be removed and recycled or disposed onshore. The exposed sections at both ends will be removed or lowered to achieve adequate depth of coverage. The existing buried sections of pipeline will be left in situ; and
– On completion of the decommissioning programmes a seabed survey will be undertaken to identify and recover debris within the platform 500m zone and a 100m wide corridor along each pipeline route.
The decommissioning operations are expected to last for a period of up to 5 years
The Cavendish gas field was discovered in 1989 in the Southern Gas Basin of the UK North Sea and development sanction was granted in 2005. During gas production starting in 2007 the initial gas production rate of 60 to 70 MMscf/d per well decreased significantly after seven months of production.
(Source: Ineos/ – Image: Geological Society, London)