Improving Mud Removal and Simplifying Challenging Cement Design: A Deepwater Case History in the South China Sea

The study presents an innovative cement spacer fluid based on microemulsion technology and an operationally simple cement design using a water-based multifunctional polymer. A case history is described where their combination was successfully applied on a deepwater exploration well in the South China Sea. Laboratory testing, modeling, and engineering design that preceded the field operation are outlined. The spacer’s performance to clean the mud from contact surfaces was verified with the goniometer method. Mud/spacer and spacer/cement tests for optimum compatibility were conducted and a fluid friction pressure chart for the mud-spacer-cement train at different displacement rates was generated. The results show that the designed spacer is highly effective in displacing the mud and converting an oil-wet surface to a water-wet surface, and therefore to provide a clean and water-wet surface to which cement can strongly bond. A water-based multifunctional polymer in the designed cement slurry was tested to validate its ability to adjust slurry properties for deepwater challenges. The cement slurry was easy to mix at surface, stable under downhole conditions, and had a sufficient short transition time at low temperature, preventing water and gas intrusion. Furthermore the evaluated multifunctional polymer was found to work as a stabilizer and extender as well as provide very good fluid loss, free fluid, and gas control. As a consequence, the multifunctional polymer reduces the total number and amount of required chemicals, thereby simplifying logistics and operations for deepwater wells. The presented spacer and cementing technologies contribute to successful zonal isolation of deepwater wells and so minimize risks as well as expensive rig and nonproductive times due to remedial work.