Cement plugs are set for various objectives: to plug back a zone or a well, sidetrack above a fish or initiate directional drilling, protect a low-pressure zone during a workover treatment or solve a lost circulation problem. It has been demonstrated that more challenges are sometimes found during the design and execution of a cement plug job than that of a primary cementing job, and thus its complexity and criticality of key steps should not be underestimated. Setting of cement plugs in open hole has historically been a challenging and expensive operation when a well is being abandoned. Current industry habits and practices avoid setting balanced cement plugs over 800 ft. However, advances in cement plug placement procedures, hydraulics modeling and cement slurry testing have notably increased the rate of success of longer plugs, which has encouraged drilling operators to set balanced cement plugs over 1,500 ft. If the objective is to place a plug over 1,500 ft, multiple cement plugs are typically placed due to concerns of plug quality and getting the workstring stuck while pulling out. The cost associated with such successive operations may represent millions of dollars in a deepwater environment even when the operation is performed with no operational failures. To minimize the costs, several plug placement methods have been explored by many oil and gas operators to set long cement plugs, with the use of mechanical or hydraulical disconnect tools and sacrificial pipes identified as one of the most feasible options. This paper reviews the engineering considerations to minimize operational risks and plug placement design challenges when sacrificial pipes are used. Field examples are analyzed in this paper, detailing first an unsuccessful case from which valuable lessons were learned, and successful cases including what is considered as one of the longest openhole plug and abandonment performed in a single job in the industry: a 6,500-ft sacrificial stinger cement plug.
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