Minimizing the Risk of Casing Failures Across Plastic Salts with Tailored Cements and Software Analysis: Case Histories from the Williston Basin, North Dakota

Abstract

Abstract A significant challenge associated with cementing across salt zones in the Williston basin is mitigating risks of casing collapse or deformation. An operator (Operator A) in this area reported that six of their old wells experienced casing failures/deformation caused by salt creep. Post-job analysis showed that these older wells used conventional cement designs. Based on the lessons learned from successful cement jobs for other operators in the same region and knowledge about salt creep loads, tailored fluid systems were proposed with optimized job design and placement procedures for Operator A's upcoming wells. This study demonstrates the benefits of the proposed modifications by comparing the logs and outcomes of old and new wells. Through post-job analysis, this study highlights the importance of using cementing simulation and modeling software to design a dependable barrier. The casing inspection logs and cement bond logs across salts from old wells indicated that deformation occurred within a few weeks of cementing. The use of a tailored cement system with enhanced mechanical properties, along with specialized spacer systems and effective centralization, showed improvement in bond logs, no casing deformation, and better casing-cement bonding in the new wells for Operator A. Pre-job simulations were performed using in-house cementing software to verify the cement job and to help ensure that the cement was effectively placed in the annulus. Cement sheath integrity modeling software was used to simulate the actual exerted loads from plastic salt formations and subsequent drilling, completion, and production operations. This software uses a semi-empirical creep law that describes the creep process of a wide variety of salts. The cement system with enhanced mechanical properties showed sufficient endurance to provide a dependable barrier to the salt creep loads experienced in Williston basin wells. Although the use of salt vs. salt-free slurries is debated for salt zone cementing, this study shows that salt-free cements with enhanced mechanical properties can be used successfully when there is no risk of cement gelation during placement. North Dakota salts principally contain halite (NaCl), which does not pose a risk of gelation. The case histories and field studies discussed establish cement systems and practices that can help to minimize the risk of casing deformation and improve the cement bond across salt zones in the Williston basin in North Dakota. This tailoring tool, with its unique ability to exert salt creep loads, helps to minimize the risk of cement sheath failure through tailored barrier designs. This information should help the petroleum industry to address long-term well integrity problems associated with cementing across plastic salts.