Exploration deepwater wells demand proper planning to mitigate any potential risks during well construction where uncertainty can play an important role. For this reason, designing dependable barriers under such a scenario requires innovative techniques, such as Managed Pressure Cementing (MPC). Using Managed Pressure Drilling (MPD), the operator can control the wellbore pressure while drilling each section. This unconventional solution for a short operational window has been successfully applied in some fields around the world, with additional advantages when cementing jobs are designed and executed.
The tight operational window expected for a 9-5/8-in. liner and the presence of gas were the main drivers to analyze the most likely scenarios for the cement job. The analysis describes that by managing the hydrostatic pressure of the fluids by applying pressure in the backside makes it possible to maintain control of the wellbore—without influxes or losses—before, during, and after the cement job. Nevertheless, to achieve the most reliable hydraulic modeling, critical parameters were identified for use as part of the input for a state-of-art cement simulator.
The scope of the cementing job for this case study was designed using a state-of-the-art simulation software to determine expected hydraulics outcomes. The main target was to maintain the bottomhole Equivalent Circulating Density (ECD) between 12.2 and 12.4 ppg during the entire cementing job operation. This 0.2-ppg margin was achieved by applying designed Surface Back Pressure (SBP) by using an MPC operational technique and finishing in a statically overbalanced condition. Dynamic pore-pressure and leak-off tests performed before the cement job confirmed the operating window. The information obtained was analyzed using appropriate software. This previous data was important to define appropriate fluids volumes and design to calculate the minimum SBP necessary for the safe execution of the job, always aiming to reduce chances of kicks and mitigate losses.
The cementing operation was performed according to the planned procedure, with no deviations, and the cementing job was performed in accord with the pumping schedule and SBP. Displacement was completed with zero mud losses, and lift pressure was observed as expected. MPC is a recommended method for zonal isolation in such cases as a small operational window, even more so when challenging deepwater scenarios are encountered. A case study of this cementing job is presented in this paper to discuss the planning process, details of the execution, and lessons learned.