Casing Design Implications of Managed Pressure Drilling and Cementing, and How to Consider Them in the Design of the Well and Operations

Managed pressure drilling (MPD) and managed pressure cementing (MPC) typically use lighter fluids than in conventional drilling. One consequence of this is that the fluid behind the casing being run and cemented is lighter than would be the case with conventional drilling. This has implications to the casing design for two reasons: the burst loads on the casing are augmented due to the lower external density profile, and the annular pressure buildup (APB) loads are different. It is important to consider these design implications while performing the casing design, particularly for deepwater wells. Unfortunately, this is not common at present, since the MPD/MPC design work and the casing design work are often distinct and separate, both physically and temporally. When the lower density external fluid from MPD/MPC is considered in the casing design, it is possible that the casing in question has to be upgraded (increased weight and grade) to accommodate the loads post MPD/MPC. This paper presents such a case, where the consequence of having drilled the section using MPD and cementing the casing using MPC was to upgrade the casing. The paper further presents a solution to this problem- modifying the MPC procedures such that a heavier mud than that used during MPD can be placed above the top of the cement behind the casing, thus mitigating the loads and eliminating the need for a heavier or higher-grade casing. The authors show how this can be achieved, by managing the densities of the different fluids and cement during the MPC operation. The authors hope that this work highlights the interconnectedness of well design and MPD/MPC operations, and engenders more interaction between the two groups during well engineering.