Minimizing the Risk of Casing Failures in Multi-Frac Horizontal Shale Wells Case Studies

Hydraulic fracturing induces high stresses in tubular components used in the construction of multi-frac horizontal shale wells. Ever since this process was adopted by the oil and gas industry to produce from tight shale formations there have been numerous very expensive failures that occur during these hydraulic fracturing operations. Many failures have been attributed to environmentally assisted cracking (EAC) of high strength API 5CT steel tubulars such as grade P110 casing and couplings. Some factors that aggravated these casing failures when exposed to high cyclic frac loads and corrosive environments was the lack of proper manufacturing processes, poor quality assurance, inspection plans, and the use of standard high yield API connections with inherently high make-up stresses. Another interesting failure mechanism is casing deformation due to formation movements from close proximity fracking operations and microbial influenced corrosion (MIC).

The industry has learned from these failures and some operators have adopted lessons learned to well designs that minimize the risk of future failures. However, adopting these learnings into well designs can substantially increase the cost of completing these wells and operators often struggle between cost and optimal well design. Some of the main well design modifications include the use of lower make-up stress connections, specifying lower yield strength materials, including a well-defined pipe purchasing process with a detailed pipe/manufacturing process specification and an ITP and QA plan (inspection and testing plan and quality assurance plan).

This presentation will illustrate several failure analysis case histories related to EAC and corrosion fatigue of standard API and modified buttress connections. The operational state of stress on some of these connections will also be discussed. Additionally, some recommended best practices related to connection selection, enhanced API 5CT material specification requirements and quality assurance as it relates to OCTG manufacturing will be discussed as well.