DECOMMISSIONING IN THE NORTH SEA

THE STENA SPEY WAY

Plug-and-Abandonment (P&A) is the final stage in a well’s lifecycle. After years of production the well comes to an end either because it stops producing or it’s no longer economically viable to produce. The well is then shut down and made safe – this is called Plug-and-Abandonment (P&A).

After decades of high activity in the North Sea many wells have stopped producing or are in the process of being shut down so P&A work is forecast to contribute an increasing number of rig requirements to the UK semi-submersible fleet in the near future. The downturn in 2014–16 saw a number of operators step up their P&A campaigns as reduced costs provided a financial incentive to complete work that is known and provides no financial upside. This has been evident with an increased number of P&A campaigns being performed during this period when compared to previous years and evidence of increased investment in decommissioning-focussed enterprises in the north east of Scotland. Additional driving forces behind the increase in P&A activity also include the Oil & Gas Authority (OGA) being tougher on operators with regard to their decommissioning obligations and the fact that more fields in the UKCS are nearing their Cessation of Production dates following impressive production histories. 

The table to the right shows the requirements for semi-submersibles to undertake P&A work in the UK measured in days, according to IHS Markit. Whilst not an exhaustive list of all potential P&A programmes, the chart clearly shows that there is a huge requirement for rig days to complete the P&A campaigns currently planned. This amounts to over 5,700 days of rig time, or 15.5 rig-years of work over a 5-year period. 

Despite this large backlog of future P&A requirements a lack of recent activity in the UKCS has resulted in the active rig fleet shrinking year-on-year as rig contractors cold stack rigs, that were once icons of North Sea, in various ports along the east coast of Scotland. Given the high costs associated with reactivation it is unlikely that any of these units will return to the active fleet in the near term leaving a potential undersupply of P&A-suitable units to perform this huge scope of work. 

In recent years, one ‘grand old lady’ of the North Sea has countered this trend. The Stena Spey has been operational in the North Sea for almost 40 years and has developed a reputation for operational excellence with an experienced rig crew that is focussed on completing any task set out before them safely and efficiently. The vessel is well suited to perform P&A activities and has recently been contracted for a 10-well campaign offshore Ireland.

The rig features certain technical capabilities which are beneficial for P&A activities, the foremost of those being an 80Mt crane installed on the aft of the rig. The installation of this crane in 2013 has been critical to the vessel continuing to secure work in recent years as opportunities in the UKCS market started to decline.. The additional capacity of the aft crane ensures that handling and off-loading of the Client’s key production equipment (mainly the so-called Christmas- or ‘Xmas’ Trees – short XT’s) can be done with relative ease. With a large crane capacity there is no longer a need to break down XTs in parts on the deck once recovered to the surface. Supply vessels are also able to operate further from the aft end of the rig when XTs are being unloaded which provides greater flexibility and increased safety when offloading equipment to send to shore. In addition, structural strengthening of the aft deck has given the rig the capability to comfortably handle multiple XTs which further minimises the impact of weather delays associated with getting this heavy equipment off the rig.

The Stena Spey has another unique advantage over many of its peers with regards to subsea P&A. Wellhead fatigue is a critical factor in the planning of most P&A well activities, and increases in Blow Out Preventer (BOP) weights over recent years mean that the BOP on many rigs today simply are too heavy to land on the wellhead given the anticipated fatigue life remaining. One solution for this is BOP tethering, however this adds increased cost and online installation time to the operation, all of which are disadvantageous when trying to achieve a cost-efficient abandonment of wells. Following retirements of other more mature units, the Stena Spey is understood to now have the ‘lightest BOP’ in the North Sea which is a significant benefit for operators when planning their P&A activities.

Over the years the rig has installed many of the equipment spreads required for P&A activities, taking and applying lessons learned from previous operations to the benefit of current clients and their 3rd Party contractors. This continual sharing of lessons with the wider community all results in a safer offshore environment across industry to complete these outstanding P&A campaigns.

One of the biggest challenges associated with P&A operations is re-entering wells that are 20-30 years old. By conquering these challenges one well at a time we continue to develop our knowledge as an industry as we establish safer and more efficient methods of completing these abandonment activities. Given the challenges ahead continued co-operation between all stakeholders is vital to ensure that we have the required technology, personnel and rig availability in the UKCS basin to safely complete the planned decommissioning activities.

“It’s exactly what we expected from Stena, having worked with them before we knew they were a very professional outfit.”

Laurie Phillips, AGR, Well team Leader

“The Stena Spey has exceeded my expectations during the Kinsale decommissioning program. Plug and Abandonment operations are normally fraught with a high degree of uncertainty.  In the case of the Spey’s campaign in Ireland the wells had been drilled over 20 years previously.  The team of the Stena Spey and AGR cooperated to solve a variety of downhole challenges in a professional manner, whilst maintaining an excellent safety record.”

Chris Carbaugh, Stena Drilling, Chief Operations Officer

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