After a well’s productive life, plug and abandonment (P&A) techniques are often used to secure wellbore isolation. Several challenges exist associated with placing cement plugs in open and cased holes, particularly in highly deviated wells. The primary factor for inadequate isolation is cement contamination resulting from intermixing of mud when placing cement plugs using conventional techniques. A solution to be able to place cement plugs during the first attempt and help prevent nonproductive time or additional rig costs was necessary; therefore, a tool was designed to address the challenges associated with setting cement plugs and has been used as a best practice to help ensure competent cement plugs.

The innovative disconnect tool was conceived as part of a solution for placing competent long-length cement plugs on the first attempt because of mechanical limitations faced when attempting to set multiple conventional cement plugs per interval. The tool connects drillable or nondrillable sacrificial tubing to the work string and provides the ability to disconnect the work string at the top of cement, leaving the sacrificial tubing in place. This process allows operators to place long cement volumes in one trip to cover the desired zones. While the tool leaves the sacrificial tubing in situ, the cement plug is undisturbed, minimizing possible contamination.

Seven deepwater wells were abandoned during a recent campaign in Angola using the high-performance disconnect tool. Using this tool provided more than USD 4 million in savings attributed to reduced rig time, which helped address the overall challenge of reducing well abandonment time. The tool performed successfully in all wells on the first attempt and passed the necessary isolation tests.

The engineered procedure, lessons learned, and quality assurance/procedure created during the preparation stage are presented, along with the engineering methodology and full analysis of potential challenges. This case study is an addition to the growing number of successful projects within the region that are helping achieve the planned objective with significantly reduced rig time.

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