Managed Pressure Cementing MPC within a Narrow Pressure Window, Deepwater Gulf of Mexico Application

Abstract

Managed pressure cementing (MPC) is an important technique for primary cementing operations in wells with narrow pressure margins between the pore and fracture gradients. This paper presents the design considerations, methodology and results of two deepwater MPC operations conducted to cement production casing strings within a target operating window of approximately three tenths of a pound. Slurry densities commonly lead to high equivalent circulating density (ECD) levels during cementing operations. This condition, combined with mud weights conventionally designed to be above pore pressure, typically results in downhole pressures which approach or exceed the fracture limit. Commonly, operators implement strategies to mitigate undesired results during the cementing phase, however, in most cases the root cause of the problem cannot be adequately addressed by taking a conventional approach. Modern transient hydraulic modeling software permit the calculation of adequate surface pressure levels to control the annular pressure profile during the different stages of a cementing operation. Based on a predetermined annular pressure target, different variables can be designed to produce surface and downhole pressures within existing limits of a particular operation. This capability combined with modern managed pressure drilling (MPD) systems enables accurate control of the annular pressure profile during cementing and allows obtaining near constant bottomhole pressures (BHP) throughout the cement placement operation while using statically underbalanced mud columns. This case study presents an overview of the engineering process used to plan and design the managed pressure cementing operations on two wells and the results obtained. The results of this study demonstrate the advantages of using modern MPD systems over the conventional approach when it comes to primary cementing within narrow downhole pressure windows often encountered during deepwater drilling operations.