Tailored and Reliable Method for Cement Plug Improves Times in Deep Water

Abstract

End-of-well operations can improve drilling performance through selection of the proper tools to optimize rig time and tailoring solutions. For deepwater projects, it is necessary to optimize costs without compromising safety and quality while delivering maximum efficiency. An innovative technique is presented for placing a long cementing plug using sacrificial tubing and a special tool. This method also allowed checking the top of cement (TOC) after a short waiting on cement (WOC) period. Plugging and abandonment operations were performed in deepwater wells in the Caribbean Sea, saving up to two days of rig time by using a single intervention to isolate the openhole length from 600 to 1500 m and allowing continued, timely operations. A case study of this operation is presented that discusses the experience and lessons acquired, which should be beneficial for the industry. Conventional balanced plugs are not efficient in openhole lengths greater than 500 ft because of operational limitations and design considerations. In such scenarios, fit-for-purpose downhole tools can provide reliable solutions, such as using a release mechanism to safely place a cement plug of the necessary length with proper thickening time distributed along the volume pumped. This technique avoids the long WOC times necessary to achieve adequate compressive strength. The release tool enables running sacrificial pipe; placing cement through the sacrificial pipe; displacing cement slurry with a dart, which provides an indication of its latching at the surface; and disconnecting to retrieve the landing string. In the laboratory, a 500-psi slurry compressive strength was obtained after 6 hours and 15 minutes. This allowed the TOC to be tagged after 6 hours of WOC. Because this procedure does not require the 3 1/2-in. stinger to be pulled out of the plug, the risk of spacer contamination in the slurry was reduced. Based on laboratory results, three operations using the release tool and discussed design considerations were performed successfully for the first time in the Caribbean Sea, with no nonproductive time (NPT) or quality issues experienced, saving up to USD 500,000 for the operator. Laboratory tests, such as compressive strength, provided a good indication of the time necessary to tag the TOC, which met the operation objectives. The tool capabilities and operational and design considerations can be used as a reference for projects in similar environments that require alternatives with proven solutions. The main benefit was reduced operator costs for rig daily charges resulting from placing one plug rather than several balanced plugs. This was also beneficial for the mud company because a large spacer volume was not incorporated into the mud. Another benefit was allowing tagging of the plug in the same operation because of the short WOC.