Decommissioning in the North Sea The Stena Spey Way…

Plug-and-abandonment (P&A) work is forecast to contribute an increasing number of rig requirements to the UK semi-sumbersible fleet in the near future.

The downturn in 2014–16 saw a number of operators step up their P&A campaign preparation 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 the years prior and evidence of increased investment in decommissioning focused enterprises in the northeast 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 (COP) dates following impressive production histories.

The table below shows the requirements for semi-submersibles to undertake P&A work in the UK measured in days, of which IHS Markit is currently aware. Whilst not an exhaustive list of all potential P&A programmes, the chart clearly shows that there is a huge requirement of rig days to complete the planned P&A campaigns in the event they occur as currently time-lined. This amounts to over 6300 days of rig time, or 17 rig-years of work over a 5-year period.

Despite this large back stock 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 the North Sea at 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 when decisions are made to safely P&A the outstanding well stock.

In recent years there has been one of the North Sea ‘old guard’ countering 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 are focused on completing the 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 batch ten well abandonment campaign offshore Ireland.

The rig boasts technical features 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 below the level of available supply. The additional capacity of the aft crane ensures that handling and off-loading of Client XTs once pulled through the moonpool can be done with relative ease. There is no requirement to break down XTs on the deck once recovered to surface due to crane limitations, and PSVs are able to sit further from the aft end of the rig when XTs are being unloaded which provides greater flexibility when offloading equipment to send to shore. In addition, structural analysis of the aft deck and strengthening modifications means that the rig can comfortably handle multiple XTs which further minimises the impact of weather delays associated with getting this heavy equipment off the rig once through the moon pool.

The Stena Spey has another unique advantage over many of its peers with regards subsea P&A. Wellhead integrity is a critical factor in the planning of most P&A well activities, and increases in BOP weights over recent years mean that many rigs simply have too heavy a BOP to land on the wellhead given the anticipated condition following an extended service life. 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 mature UKCS 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, whether it be for Bleed Off rig-ups, Coiled Tubing installations, EDP/LRP stack-ups, swarf handling optimisation or the safe handling of dual bore riser systems on the rig floor, 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 to 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.

Stena Drilling is one of the world's foremost independent drilling contractors, consisting of 4 ultra-deepwater drillships and 2 semi-submersible rigs. For more information visit: www.stena-drilling.com

Read the latest issue of the OGV Energy magazine HERE.