Challenge
As outsourced Well Operator, a requirement existed to remediate the Downhole Safety Valves (DHSVs) on wells B2z and B4 on the Babbage platform in order to restore well integrity and support continued gas production from this mature Southern North Sea asset. The B2z DHSV failed to fully close, likely due to halite scale build-up, while the B4 DHSV demonstrated a “sticky” operating mechanism during operation. These issues posed a risk to barrier integrity and threatened production continuity, with the potential for deferred production if left unresolved. As the asset operates in a constrained offshore environment, the intervention also had to be carefully planned to minimise offshore duration, reduce cost and personnel exposure, and limit disruption to ongoing platform operations, while maintaining full regulatory compliance.
Solution
THREE60 Energy delivered a fully project managed well intervention campaign using an optimised slickline approach, selecting the Wellvene WellHOP system in place of conventional wireline methods to significantly reduce rig-up and rig- down time. A structured intervention programme was executed, comprising drift runs, DHSV verification, mechanical cleaning with a 360° radial brush, and chemical soaking with heated fluids to remove halite scale. Efficient well-to-well transfer processes were implemented to minimise downtime between interventions, while proactive engineering, planning, and risk management ensured full regulatory compliance and effective mitigation of operational risk.
Result
The campaign successfully restored both B2z and B4 DHSVs, with valves passing final testing and achieving acceptable leak rates, thereby reinstating barrier integrity and enabling continued production. The use of the WellHOP system reduced rig-up and rig-down time from 178 hours to 32 hours, delivering a saving of approximately 146 hours and a cost reduction of around £131k. Shorter offshore duration reduced personnel exposure and overall operational risk, while improved efficiency enabled more interventions to be completed within the campaign window. The operation was completed safely with no HSE incidents and benefitted from a smaller offshore footprint and reduced crane usage, allowing normal platform operations to continue while carrying out the intervention campaign.
