A Causation Investigation for Observed Casing Failures Occurring During Fracturing Operations

Abstract

The objective of this paper is to present findings from a causation investigation of casing failures occurring during fracturing operations. The study analyzed case histories and examined post-failure laboratory results. Outcomes from casing failures include blowouts, pollution, injuries/fatalities, and loss of the well with associated costs. This work has not been previously published nor is this type of work available in the public domain literature. This study cataloged pertinent data from fourteen (14) land-based case histories of casing failures while fracturing. The case histories were analyzed with the use of photographic evidence of recovered casing, well reports, fracturing treatment data, drilling records, and laboratory testing of recovered casing when available. Failure causes were identified. Preliminary guidelines are provided to avoid casing failures and mitigate the damages. Recovery guidelines are presented. A model was developed to evaluate axial loads under several considerations associated with fracturing. The model accounted for the casing's in-air load, buoyancy effects from wellbore fluids, piston effect, bending, erosion, and temperature decreases. The combined loads were compared to the casing's yield strength. The failures were not systemic but included cracking related to fatigue, hydrogen and sulfide stress embrittlement, and erosion at ERW weld lines. The failures were observed at various well depths, both in the cemented and uncemented hole sections. Results address common casing sizes and couplings involved with each failure, weight and grade, failure location and causation identification of other factors contributing to the failure. A goal of this investigation and on-going work is to develop a thorough understanding of casing failures and the myriad of contributing factors in order to develop a comprehensive predictive model for land and offshore fracturing operations.

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