BLACKBACK SUBSEA A1A REMOTE WELL KILL

Abstract

Esso Australia Pty Ltd has recently completed a unique wellwork operation to secure the A1A well on its Blackback facility in Bass Strait. The Blackback facility consists of three subsea wellheads, linked in daisy-chain formation, sitting in 400 m of water depth. The field is approximately 19 km southeast of host platform Mackerel and 87 km from shore.

The Blackback A1A well recently developed leak rates through the subsurface safety valve and production master valve which exceeded Esso’s internal acceptance criteria. Production rates on the A1A well did not justify an immediate workover to restore the integrity of the passing valves. Although there were no immediate environmental concerns, inadvertent damage to the wellhead had potential to create an environmental exposure, so the decision was made to kill the well temporarily until a workover opportunity arose.

An innovative remote well kill procedure was developed, utilising the 23 km gaslift pipeline to pump kill fluids down to the well from host platform Mackerel. The procedure involved a unique and intricate shut-down procedure and pumping strategy. The main operational risks pre-identified and mitigated in the procedure included potential hydrate formation in the pipelines, over-pressure or blockage of the gaslift pipeline, and use of significant volumes of methanol for hydrate management.

The Blackback well kill operation was executed to plan, with no safety, environmental or facility related issues. The A1A well remains in a killed state with positive overbalance, while start-up of the A3 well following the procedure was successfully executed. This achievement has opened new doors for conducting well kill operations on subsea facilities, with significant cost efficiencies when compared to the alternative—mobilisation of a floating drill rig.