Use of High-Strength Alloys and Elastomers in Heavy Completion Brines

Abstract

Abstract Recent field experiences have shown that stress corrosion cracking (SCC) failures can occur when high-strength, low-alloy steels and stainless steels are exposed to heavy completion brines. SCC of super 13Cr and duplex stainless steels has also been reported in lighter CaCl2 brines that have sulfur-containing additives. Modifications of fluid composition with particular attention to additive selection and careful materials selection are required to prevent field failures of completion and service-tool hardware. The authors have performed laboratory testing to understand the interactions of completion brines that contain zinc bromide (ZnBr2) with the common metallurgical alloys used in service tools, workstring materials, and other permanent downhole equipment. There has been little published work on environmental cracking of common engineering alloys in corrosive ZnBr2 blends. Recent case histories with high-strength downhole service-tool components are described and solutions are proposed to address exposures to heavy brines. Selection of elastomers and seals for use in these environments also requires consideration of the fluid type and additive package. As a result of their testing, the authors have developed internal guidelines that require the use of severe service equipment for brines with densities higher than 17.0 lbm/gal in temperatures over 275ºF. If thiocyanate additives are required for corrosion control, careful control of the brine blend, pH modification, and/or the use of organic sulfide scavengers are recommended.