A Practical Approach to Multiwell Decommissioning

An offshore operator had seven similarly drilled deepwater wells in the Gulf of Mexico that were reaching the end of their productive lifetimes and due to be decommissioned. A consistent and practical solution was sought to abandon the seven wells while meeting the regulatory requirements laid-out by the local compliance entity. Successful implementation would offer a potential solution to similar abandonment requirements globally. Due to the nature of abandonment work, some assumptions were required during the planning and preliminary cement design phase. Detailed well information would not be available until the rig was able to latch onto the wellhead and assess the well's condition. To address this uncertainty, and allow for flexible design, the base cement slurry for each section was designed with additives exhibiting low sensitivity to certain downhole conditions. These focused on keeping the slurry thickening time stable at a range of temperatures and slurry rheology consistent with surface to downhole conditions. The operator was successful in abandoning the seven wells as per the regulatory requirements, with 45 cement barriers put into place. Applying similar designs from one well to the next allowed for faster cement design turnaround and improved materials management. Using innovative solutions, the challenges controlling the slurry behavior at varying conditions were overcome. Cement additive concentrations were refined over the course of the project, but the iterative approach meant that fewer changes were needed later in the project due to the increase in operational experience and design data. Contingency cement systems were prepared ahead of, and continuously updated during, the project to address probable risks, adding to the database of slurries that could be referenced for future work and potentially increasing planning efficiency. Developing this standardized process approach to well decommissioning saved an average of 11 days per well, 32% of the time, when comparing the first three and the last three wells. Using a similar model, a more effective decommissioning plan can be created to conceivably allow for an increase in the scope of future abandonment projects to offset time savings. This process can be tailored to offshore and land wells around the world, especially where similarly behaving cement materials are locally available.