Plug and Abandonment Using Reverse Cement Placement Technique in Deepwater Gulf of Mexico

摘要

Four deepwater wells in the Gulf of Mexico were identified for permanent abandonment in accordancewith local regulations. The abandonment plan called for multiple cement plugs to isolate the productionzones from seabed in each well. The most challenging cement plugs in each well were the ones directlyabove the production packer isolating the casing-tubing annulus and the production tubing. To avoidcement left in the Christmas tree at seabed and potential plugging off any valves in the manifold, cementplugs could not be placed the direct way, pumping down the production tubing.An unconventional approach was proposed to address the challenge. It involved reverse placement ofcement plugs, which is not common in deepwater even in these days. Using this technique, cement waspumped down the casing-production tubing annulus and, through perforations, back up the productiontubing. Risk analysis indicated very low likelihood of plugging off any valves in the tree. However, thisconfiguration did not allow use of mechanical separators between fluids to prevent intermixing. Additionalchallenges in placing the plug were the high deviation of the section and the completion brine inthe wellbore.Simulation of reverse placement is not possible with existing software. Therefore, the jobs weredesigned using experimental software, which enabled the design engineer to accurately reconstruct fieldconditions. Additional attention was given to the job procedure to minimize contamination with the brineand optimize cement placement. Viscous spacer was pumped ahead and behind the slurry to displace thebrine. The slurry was designed with low fluid loss to be squeezed through perforations in the productiontubing without plugging them off.A total of seven plugs were placed using the reverse placement technique. Specific requirements withregards to the top of cement and plug integrity had to be met before any of the cement plugs could beaccepted by the operator. All plugs were tagged and pressure tested successfully in the annulus as wellas inside the production tubing on the first attempt. As a result of the campaign, the four wells wereabandoned as per schedule and within budget.