Page 57: of Offshore Engineer Magazine (Sep/Oct 2019)

56 58

TECH FILES TA Cap Test Tool

Relieving the Pressure of Subsea P&A Activity

By Matt Manning - Engineering Manager, Unity he temporary abandonment or suspension of a well is a vital early stage of decommissioning whereby the well is isolated using methods such as bridge

Tplugs, cement squeezes and packers. This allows the wellhead and/ or blow out preventer (BOP) to be safely removed. For subsea mudline wells, temporary abandonment (TA) caps are ? tted to the hanger system, providing additional well and environmental barriers.

With high costs related to permanent subsea abandonment, suspended wells can often be in-situ for more than 10 years.

During this time, it is possible for pressure to build up in the

The TACTT can be vessel deployed, well, corrosion to take place and marine build-up to accumulate.

creating signi? cant cost savings

Source: Unity

Reentering these suspended wells can be challenging and high risk, particularly as any pressure build up behind the BPV of the TA cap and testing the pressure below. This second back pressure valve (BPV) of the TA caps cannot usually be test veri? ed zero pressure under the TA cap and provided an measured. Pressures can reach over 4,000psi which creates accurate understanding of the well’s condition, allowing the signi? cant safety concerns, so intervention is normally con- operator to make an informed decision on the next stage of ducted using a rig with heavyweight well control packages to decommissioning. Once zero pressure and well integrity was ensure safety compliances are met. However, this is subject con? rmed, the operator could safely continue with removal of to rig availability and comes with high associated costs – cur- the cap to proceed with P&A operations.

rently around £225,000 ($277,000) per day for deepwater rigs. Developed in response to industry demand, the TACTT is

Unity, a FrontRow Energy Technology Group company, able to accurately and reliably pressure test and vent suspended has developed the Temporary Abandonment Cap Test Tool mudline wells behind the TA cap prior to removal. Economic, (TACTT), a new method of pressure testing and venting sus- safety and environmental bene? ts are particularly realized when pended mudline wells prior to abandonment which contains deployed across multiple wells in region-wide vessel campaigns an integrated well control solution. The technology has re- to pressure test, survey and prepare for abandonment.

turned cost savings for independent operator Spirit Energy for Olav Log, director of drilling and wells at Spirit Energy an end of life project in the Southern North Sea. said, “Unity’s TACTT allowed Spirit Energy to successfully

The TACTT can seal onto any type and size of TA cap, pres- abandon two North Sea wells in line with UK government sure test the seal to ensure well containment, then test and regulations. The tool removed all risk associated with re-en- vent pressure from below the TA cap by stabbing the BPV tering a suspended well and the ability to deploy by vessel and leaving a reliable secondary seal in place if required. It provided signi? cant project savings. can be cable deployed from a vessel through open water using “The TACTT technology was originally designed to our a crane and hydraulic umbilical which connects to a control speci? cations and successfully deployed from a rig in the panel at surface. Vessels have greater availability than rigs, North Sea in 2014. This latest development allowing for ves- can be deployed faster and generally save between 30-50% in sel deployment opens up further opportunities.” costs when compared to rig-based intervention. A recent Oil and Gas Authority report estimates that 45%

The TACTT technology allows operators to understand the of all decommissioning expenditure in the UKCS is through amount of pressure accumulation below the TA cap since the P&A of wells. The current cost estimate of decommissioning last intervention and factor this into their decommissioning is £51 billion ($62.8 billion) with the government and industry plans. If pressure build up continues, and the BPV on the TA aiming for an ambitious 35% reduction by 2022.

cap fails to reseal effectively, the TACTT can leave a secure, There is inevitably greater pressure on operators to safely secondary seal in place to allow well reentry at a later date. and cost-effectively manage end of life wells in this unavoid-

During the Spirit Energy campaign, the TACTT was de- able phase of operations.

ployed from a vessel by crane where it was guided to the mud- This provides signi? cant opportunities for the supply chain to line well by ROVs and divers, then latched and sealed onto the evolve and deliver new technologies and methods which tackle

TA cap. The seal was pressure tested from a surface control and overhaul the key challenges. Research and development in- unit to ensure effective well containment, before stabbing the vestment and adoption of pioneering new technologies is critical.

SEPTEMBER/OCTOBER 2019 OFFSHORE ENGINEER 57