Decommissioning without a rig: P&A of remote platform wells using a W2W supply vessel

In 2023, Esso Australia successfully executed a plug and abandonment (P&A) campaign on the Perch and Dolphin monopod platforms in the Bass Strait. Faced with a spatially constrained offshore environment, the Wells Team partnered with Upstream Supply Chain to develop and engage a multi-purpose supply vessel (MPSV) with Walk to Work (W2W) capability. Both platforms were unstaffed and posed significant logistical and access challenges. The MPSV functioned as a supply vessel, with additional capability including living quarters, helideck, heave-compensated crane and W2W gangway for personnel transfer to and from the platform. A cement flowline was routed across the W2W gangway and connected via a high-pressure dry break to a corresponding flowline on each monopod. Utility lines for power, water and air were similarly deployed. The wells were killed by bullheading fluid through the cementing flowline and a slickline unit – positioned on the cellar deck of the monopod – installed mechanical plugs to secure the wells. The reservoirs were permanently abandoned by pumping through-tubing cement plugs through perforations in tubing made above the production packers. Subsequent pressure tests and top-of-cement tags verified accurate barrier placement. This campaign, completed using a novel approach, not only met regulatory requirements but also replaced scope originally planned for a jack-up rig, delivering substantial cost savings and logistical efficiencies. A detailed vessel and equipment selection process, supported by modelling, enabled the use of a versatile, dynamically positioned vessel – delivering effective execution in a challenging environment and setting a benchmark for future P&A operations on similar offshore infrastructure.