Post COP (cessation-of-production) operations are a source of expenditure with no financial return. Therefore, the focus on the cost of operations and technology is acute. The permanent abandonment of subsea wells can involve significant expense, with project logistics, interfaces and the high number of parties involved contributing to the project cost. As such, new project execution models have been developed to reduce the conveyance cost, and reduce the project interfaces.
The paper presents a novel project-managed execution model to safely execute Phase III well-abandonment operations and annulus fluid removal for surface disposal. The project used a monohull service vessel and new market technology to successfully abandon wells compliant to local and international legislation and standards. Using technology from alternative exploration sectors, allied to existing well-construction technology, presents a system that is capable of subsea well re-entry and pressure containment, to perform the permanent abandonment and safely dispose of well fluids to surface. Tubular milling, cutting and open-water recovery operations are presented and discussed, with the engineering and quality, health, safety and environment (QHSE) drivers highlighted.
Five wells were selected for the Phase III well abandonment operations using a bespoke system that was integrated into a monohull vessel, which resulted in a reduced day rate compared to a semi-submersible rig. The technology solutions taken from alternative exploration sectors are presented, and the integration to a vessel of opportunity, to provide a marine vessel with a heave compensated hoisting system and tubular handling capabilities. For well re-entry, a pressure-containing re-entry workstring is used, conveyed on drillpipe. The pressure-containing, circulation and disconnection capabilities are presented, along with how potentially pressurized and harmful wellbore fluids are taken back to the vessel for disposal. Multi-annuli perforation technology, which allows a multi-annuli well barrier to be set across the wellbore, is also described.
With five wells successfully completed, the key performance indicators (KPIs) are discussed, and project lessons learned are presented.