Influenced by statutory obligations and responsible asset stewardship, well decommissioning is the inevitable end stage of a producing field. It is becoming increasingly common now many assets are reaching the end of their productive lives, especially in the North Sea.
In Norway, the process of plugging and abandonment (P&A) follows strict guidelines defined by the Ministry of Petroleum and Energy. During the next 5-year period, up to 25% of the fields currently on stream are eligible for decommissioning as all viable (financially profitable and recoverable) reserves are depleted. Technology which can support this activity and deliver increased safety and efficiency will become more vital to the industry.
With high costs related to permanent abandonment, historically these subsea wells have been suspended or temporarily abandoned, perhaps awaiting later investment or development decisions. Many of these wells have been suspended for more than ten years, over which time it is possible for pressure to build-up, corrosion to take place and marine debris to accumulate. Re-entering these wells can be challenging and high risk, particularly as any pressure build-up cannot usually be measured.
Unity, a FrontRow Energy Technology Group company, with offices in the UK and Denmark, has developed the Temporary Abandonment Cap Test Tool (TACTT), a pioneering new method of pressure testing and venting suspended mudline wells prior to abandonment. Crucially, the technology can be deployed not only from a rig, but also through open water from a vessel to reduce cost. It has already returned substantial savings for independent operator, Spirit Energy for an end of life project in the Southern North Sea.
A vessel deployed solution
Unity’s TACTT is the first and only technology of its kind. It can seal on to any type and size of TA cap, then pressure test the seal to ensure well containment. Any pressure below the TA cap is then safely vented by stabbing the cap’s back pressure valve (BPV). If the BPV does not re-seal once the operation is complete, the TACTT can leave a reliable secondary seal in place, allowing for later re-entry.
The tool can be deployed from a vessel through open water via crane, using a cable and hydraulic umbilical controlled from surface. Financially and logistically, vessels have greater availability than rigs, can be deployed faster and generally save between 30-50% in costs when compared to rig-based intervention.
The TACTT is particularly suited to multi-well, region-wide, pre-abandonment campaigns to pressure test, survey and prepare for P&A using a vessel of opportunity. Here, the TACTT can deliver significant economic and safety benefits and allow operators to understand the amount of pressure build-up in each suspended well. This can then be factored into subsequent decommissioning plans.
Unlocking P&A opportunities in the North Sea
During the Spirit Energy project, the TACTT was deployed by crane from a vessel where it was guided to the mudline well by ROVs and divers, then latched and sealed on to the TA cap. The seal was successfully pressure tested from a surface control unit, to ensure effective well containment, before stabbing the BPV of the TA cap and testing the pressure below. This second test verified zero pressure under the TA cap and provided an accurate understanding of the well’s condition, allowing the operator to make an informed decision on the next stage of decommissioning. Once zero pressure and well integrity was confirmed, the operator could safely continue with removal of the cap and proceed with P&A operations.
Olav Log, director of drilling and wells at Spirit Energy said, “Unity’s TACTT allowed Spirit Energy to successfully abandon two North Sea wells in line with UK Government regulations. The tool removed all risk associated with re-entering a suspended well and the ability to deploy by vessel provided significant project savings.”
“The TACTT technology was originally designed to our specifications and successfully deployed from a rig in the North Sea in 2014. This latest development allowing for vessel deployment opens up further opportunities,” added Log.
New technology for ageing wells
As the North Sea continues to see more decommissioning projects sanctioned, there is greater demand and opportunity for the supply chain to adapt and develop solutions to address emerging challenges and improve historical processes.
Innovative and enabling technologies such as the TACTT will help to deliver substantial savings, efficiencies and well insights which can be shared across the industry to improve safety, collaboration and decision-making.
Michael Scott joined the Unity team in 2018 to support the company’s growth strategy, focusing on the commercialisation of Unity’s growing well integrity technology portfolio and further business expansion in global markets – notably the US, Middle East and Asia. Scott earned a Master’s Degree in Engineering, a diploma in Management Studies from The University of Aberdeen.