South Morecambe gas field lies in the UK Continental Shelf (UKCS), in block 110/8a and 110/3a license area, approximately 30km west of Blackpool in the East Irish Sea, UK.
The gas field is owned and operated by Spirit Energy. The company ceased production at drilling platform (DP) 4 in 2018 and at the DP3 platform in 2019, citing declined, sub-economic production rate from the matured field.
The DP3 and DP4 installations, along with the associated pipelines and cables, of the South Morecambe gas field were approved for decommissioning by the Offshore Petroleum Regulator for Environment & Decommissioning (OPRED) in September 2019. The decommissioning work will begin in 2020.
Details of pre-decommissioning works
Before the decommissioning of the DP3 and DP4 platforms, the 12 associated wells will be prepared for decommissioning according to Health and Safety Executive (HSE) regulations and Oil and Gas UK guidelines. The pipelines connecting the platforms with the central processing platform will be flushed and prepared for decommissioning.
The processing system at the topsides of the platforms will be cleaned and any remaining effluent will be transported to shore for disposal before removal of the platforms.
DP3 and DP4 platforms decommissioning details
The DP3 and DP4 platforms were installed in 1983 and 1984 respectively. The DP3 platform lies in 22m of water, while DP4 lies at a water depth of 25m. Each platform features six well slots and 16 conductor slots, and is supported by a four-legged steel jacket. The platforms are equipped with basic processing facilities and a utility module. DP3 features 12 skirt piles and DP4 has eight skirt piles.
The substructures of the DP3 and DP4 platforms will be dismantled using specialist equipment and transported to shore for potential re-use or recycling of the components. Approximately 22,000t of total platform infrastructure will be removed, of which more than 95% of equipment, steel and other components of the platforms will be recycled.
Decommissioning of wells and associated equipment
The 12 wells associated with the platforms will be permanently plugged and abandoned. The pipelines will be cleaned and left buried under the seabed, while the exposed ends of the pipeline will be removed and shipped to shore for recycling.
Associated protection and stabilisation components, including mattresses and grout bags, will also be recovered and recycled.
PD&MS Group received a contract for topsides decommissioning of the DP3 and DP4 platforms. The company will also be responsible for operations at the platforms at the end-stage of their lifecycle.
South Morecambe gas field details
South Morecambe gas field was discovered by the drilling of the 110/2-1 discovery well in 1974. Production from the gas field started in 1985.
The South Morecambe gas field complex consists of seven fixed jacket platforms, which encompass three manned central production complex (CPC) platforms and four normally unattended installations (NUIs), DP3, DP4, DP6 and DP8. The NUIs are tied back to the central production complex (CPC).
DP3 is situated approximately 3.5km northwest and DP4 is situated approximately 3.6km southwest to the central processing platform 1 (CPP1). The production from the DP3 and DP4 platforms was exported to CPP1 via a 24in concrete-coated gas pipeline.
The platforms received chemicals from CPP1 via a 2in monoethylene glycol line. Electric and fibre-optic cables supply power and control to the platforms. The pipelines and cables are trenched and buried into the seabed. The pipeline for gas export is concealed under a deposited rock for approximately 200m between the platforms and CPP1.