Managed-Pressure Cementing: Successful Deepwater Application

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 28139, “Managed-Pressure-Cementing Successful Application in Deepwater Exploration: Case Study,” by Alejandro De la Cruz Sasso, Halliburton, and Thiago Pinheiro da Silva and Patrick Brand, SPE, Blade Energy Partners, prepared for the 2017 Offshore Technology Conference Brasil, Rio de Janeiro, 24–26 October. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. Adverse conditions are often encountered during managed-pressure drilling (MPD). These conditions can include wellbore instability, kicks, and losses that create challenging scenarios for cementing operations, such as a narrow operational window between the pore pressure and the fracture pressure, which can compromise the necessary barrier and require unconventional solutions in deep water. This paper reviews a successful managed-pressure-cementing (MPC) operation and presents findings and lessons learned. Introduction The case in this paper is an exploratory well drilled at a water depth of 1700 m in the Caribbean Sea. Well 1 was designed to drill through a potential shallow gas interval directly below a 22-in. shoe using MPD. A total length of 350 m of 22-in. open hole was drilled to the 18-in.-casing point. An unexpected high-pressure water/gas sand was encountered below the 22-in. shoe with a pore pressure of approximately 9.85 lbm/gal. The fracture pressure at the 22-in. shoe was measured to be 9.9 lbm/gal, which leaves a narrow operational window of 0.05 lbm/gal. The strength of the 22-in. shoe was confirmed by a dynamic formation-integrity test. A conventional cement operation was not feasible because of the required mud-weight (MW) increment and the resulting equivalent circulating density (ECD) with the 18-in. liner at the bottom, which limited the likelihood of success. The use of a high-strength, low-density slurry weighted to 11.5 lbm/gal was considered but was rejected because of the additional time and logistics required for a special cement-slurry dry blend. This resulted in the decision to implement MPC to increase the probability of achieving a barrier in place through the 18-in.-liner shoe and overlap the previous casing shoe. MPC Overview Cementing through MPD equipment is known as MPC, where pressure is applied at surface throughout the cementing operation to maintain an overbalanced environment. During the engineering and planning phases, discussions and reviews were conducted with all companies involved to analyze different scenarios. On the basis of these discussions and reviews, a target ECD for the cementing operation was established. The anchor point used was defined at a 22-in.-shoe depth, with a value between 9.85 and 9.9 lbm/gal, which was suitable for avoiding un desired wellbore-fluid influxes and losses. The anchor point is a defined depth in the open hole at which ECD values are kept steady using the MPD choke to provide overbalanced conditions without exceeding the fracture gradient. At such conditions, the cement was designed with cementing software. MPC Operation Considerations Precementing operations were defined to help provide optimal safety and reliability for MPC execution. These operations included the following.