One of the Largest Volume Deepwater Cementing Operations Performed Globally

Abstract This paper will present a case study describing a challenging, large volume, cementing operation, executed in a deepwater environment. The paper provides insight and knowledge regarding the experience that helped develop best practices for successfully completing similar designs. The Leviathan Basin in the Eastern Mediterranean area, near Israel, is notorious for its unconsolidated salt layer directly beneath the seafloor. Historically, this has prevented many riserless sections from achieving cement to seabed due to wellbore washouts and lost circulation. To achieve the objective of bringing cement to the seabed, the proposed solution was to apply a high annular volume slurry excess (an average of 342%) and extend the surface casing length to 950 m to pass through the critical salt zone. Due to the high salt concentration in the slurry design, the entire volume of mix fluid (4,110 bbls 653 m3) had to be prepared in rig pits. To ensure the success of the operation, several out-of-the-ordinary measures had to be taken, such as performing the periodic maintenance 3 months ahead of schedule, before the operation, replacing all consumables that might cause leaks (pump packings, valves, seats, centrifugal pumps). For pit management, rig piping was split into two parts with one part accommodating drilling fluids and the other the cementing mix fluid. Each part had its own dedicated lines and pumps, to avoid any cross-contamination. Through the implementation of tailored best practices, the cementing operation was executed flawlessly with more than 14 h of continuously pumping a total volume of 4,825 bbls 767 m3 of cement slurry. It was noted that only 710 bbls 113 m3 of slurry returned to the seabed, therefore confirming the wellbore was significantly washed out (enlarged), and the strategy of using a high excess volume was appropriate. No loss circulation was encountered during the operation. Zonal isolation for the section was achieved with successful casing cementation. The slurry design incorporated a short wait-on-cement time of 07:30 hrs:min to 50 psi and 12:30 hrs:min to 500 psi, despite the extended pumping time. The ultimate verification test of the cementing operation became apparent with a successful formation integrity test (FIT). The drilling program continued, as per schedule. To ensure the success of the operation and mitigate any equipment issues, the slurry itself was designed with a 1 hr. stop-start pumping time, vs. the usual 20 min. The rig drains were kept available throughout the job so on the off chance the equipment had a malfunction, the crew would have enough time to troubleshoot and fix any issues. The long stoppage time permitted the cessation of pumping, dumping the cement, washing the unit, and then restarting the slurry mixing, in case there was any observed cement settling or plugged lines. This paper uses a case study to present a series of best practices that include design, logistics, and execution. These practices help to improve the safety, quality, and efficiency of large volume cement operations. This experience can be readily translated to other operations with a similar scenario.