Minimizing NPT: The Elimination of Cement Plug Failures in the Western US

Abstract

Industry-wide cement plug failures account for more than 1,000 hours of lost time and USD 20 million in nonproductive time (NPT) costs each year, including individual failures responsible for up to 350 hours of lost time and USD 3 million in NPT costs. These failures include unset or soft cement that cannot meet the plug requirements, top of cement not at the designed depth, loss of cement plug, and stuck pipe. The causes of cement plug failures include incorrect temperatures, slurry contamination, cement falling in the wellbore, and inadequate displacement methods.Best practices applied during a new process include temperature mapping of major fields, evaluation of the plug base, implementation of mechanical fluid separation, optimization of balancing fluids while pulling out of hole, and mathematical modeling of fluid contamination. The peer-review process for the design answers four simple questions: Is the design documentation complete and accurate? Does the design meet a clearly defined client objective? Does the design adhere to plug cementing best practices? Is the cementing crew prepared to properly execute the job?In 2012, nine western US cement plug failures resulted in over 200 hours of lost time and USD 500,000 in NPT costs. The lack of technical design criteria and accountability process demonstrated the need for improvement. In response, a regional investigation and quality initiative were launched. The investigation found regional failures related to cement contamination, incorrect displacement, poor slurry design, and incorrect well data. As a result, a specific process for handling all plug cement jobs was implemented. This process included adherence to a number of plug cementing best practices and a peer-review of all plug cement designs.Approximately 500 cement plug jobs have been executed within the last 27 months in the western US region since the implementation of the plug cementing process. In this time, there have been no plug failures, no NPT, and no rig costs from failed cement plug operations.