In deepwater Gulf of Mexico, cement placement through coiled tubing (CT) has been proven over several decades to be a valuable, versatile, and cost-effective tool for the through-tubing plug and abandonment of depleted oil and gas producers. In this paper, several present-day recommendations and best practices in relation to CT cementing for well abandonment are described.

CT cementing is typically used for well abandonment when leaving part of the production tubing in place is deemed beneficial from an economic or operational risk standpoint. As demand for the reliable placement of permanent cement barriers during well abandonment continues to grow, the importance of optimal design methodology, laboratory practices, and placement techniques associated with CT cementing has also increased. For instance, one of the most important aspects is to design a thin yet stable cement slurry. In addition, thickening time tests must account for the time a slurry is in the CT reel at surface before travelling downhole. Fluid placement techniques should account for the use of any downhole tools and be adjusted accordingly.

In recent well abandonments, a high success rate in the placement of cement plugs through CT has been observed. The main contributor to this success is the consistent manner in which the best practices described in this paper were followed. These methodologies also include some that have slowly evolved over time. For example, during well abandonment, one procedure that appears to be gaining popularity in some situations is the running of inflatable cement retainers with the ball on seat. In regards to CT cementing, this has often resulted in modified strategies, with fluid placement techniques counteracting the inability to pump any fluids through the CT prior to setting the retainer.

This paper is based on several recent abandonment campaigns using an intervention vessel in the Gulf of Mexico in 2016. Throughout the course of these particular campaigns, a total of 32 cement plugs were placed through CT, all of which were successfully verified, thus avoiding costly remedial placement. Although different conditions and well-specific challenges can slightly alter the approach taken, there are several steadfast techniques that appear to be effective in the consistent delivery of desired results.

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