Case Study: Annular Isolation Using A Hydro-Mechanical Expansion Plug & Perforator

Abstract This paper details the design, installation, and verification of the upper abandonment cement plug on a seven well abandonment campaign in the Bass Strait. A final abandonment plug was required across the 9-5/8″ casing and 9-5/8″ × 13-3/8″ casing annulus as the final pressure-containing barrier. The paper discusses evaluating verification methods, while addressing concerns from the Australian regulator regarding cement slumping in the annulus and its potential impact on long-term barrier integrity in the well abandonment strategy. To prevent cement slumping within the 9-5/8″ casing, a bridge plug is typically used; however, no equivalent solution exists for the casing annulus. Traditional methods, such as squeezing viscous pills into the annulus, face limitations due to weak loss zones, cement displacement complications, and verification difficulties. A mechanical solution was explored by means of a hydro-mechanical expansion packer designed to expand the 9-5/8″ casing against the 13-3/8″ casing ID, forming a base for the annular cement squeeze. The hydro-mechanical expansion packer (MPX) and associated mechanical barrier strategy were successfully deployed during abandonment operations on the Basker, Manta, and Gummy well campaign. Following preparatory operations, the 838 MPX was run and set at approximately 3215 ft (980 m), forming a mechanical support barrier for the annular cement squeeze. A hydro-mechanical perforating tool was used to perforate the 9-5/8″ casing immediately above the MPX dual annular plug and just below the wellhead to provide access to the 9-5/8″ × 13-3/8″ annulus. This enabled annular circulation and conditioning prior to the cement squeeze. Flow checks confirmed the well was static and free of hydrocarbons. A 325 ft (100 m) cement plug was then placed into the annulus and casing bore above the dual annulus plug, and pressure tested to 1250 psi for 15 minutes, with a 4.5 t set-down to tag the cement plug confirming placement integrity. All cement plugs were tagged within the required depth confirming the MPX expansion and isolation of the annulus with no cement slumping. The MPX approach mitigated cement slumping risk, enabled effective annular support, and reduced the need for high-pressure testing across sensitive casing. This paper presents a novel mechanical solution to prevent cement slumping in casing annuli during well abandonment – a long-standing industry challenge. The deployment of the hydro-mechanical expansion packer to expand casing and form a support barrier in the outer annulus represents an innovative solution in offshore abandonments. It offers an alternative to traditional viscous pill methods, improving barrier integrity, regulatory compliance, and operational efficiency in complex well environments.

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