Abstract
Casing in extreme-temperature sour wells must withstand severe loading, including large temperature excursions, cyclic plastic deformation, and exposure to sour environments. Those conditions lead to synergistic material damage where different degradation mechanisms accelerate one another. Current understanding of synergies between thermo-mechanical loading and sour corrosion-cracking is limited. No industry standard exists for evaluation of tubular materials under such combined loading.
The evaluation methodology presented here was developed to assess material performance under combined thermo-mechanical loading and environmental exposure, enable a rigorous selection of materials for extreme-service sour wells, and contribute to thermal well integrity. The development commenced with defining a complex laboratory test (SRT) that closely simulates loading in thermal operations. The SRT was executed on reduced-scale specimens of four OCTG materials, which were ranked according to their ductility loss and observed fracture mechanisms. Those results were compared with several simplified tests to identify dominant synergistic-damage mechanisms; and determine the test complexity required to accurately simulate the synergistic conditions.
While the methodology development is ongoing, this paper presents key results from the SRTs and simplified tests. Rankings based on various tests complexities demonstrates significance of concurrent post-yield loading and sour exposure, and reinforces the need for an assessment methodology that properly simulates these combined loading/exposure effects.