Corrosion Resistant Alloys Test Protocol Development and Results for an Ultra Sour Reservoir Containing Elemental Sulphur

Abstract

Abstract Corrosion of Oil Country Tubular Goods (OCTG) is a traditional concern in the Oil and Gas industry, as it represents a major component of well integrity management. Various corrosion mechanisms may affect the performance of materials in downhole applications, especially in corrosive environments containing large amounts of H2S, CO2, and Chlorides. In high sour environments, elemental Sulphur may also be present, in which case, it will act as a strong oxidizer, affecting the performance of the material selected. In this paper, a test methodology was developed to selected a technoeconomical fit for purpose material for application in the development of a Ultra Sour Reservoir Containing Elemental Sulphur. This methodology consisted in evaluation of the SCC (Stress Corrosion Cracking) behaviour of Corrosion Resistant Alloys (CRA) of group 4D, as per ISO15156-3/ NACE MR0175-3, at the border between 4D and 4E environmental limits including the simultaneous presence of dissolved and elemental Sulphur in the fluid. A testing set-up was developed to ensure the contact of elemental S with the material in order to ensure the strong oxidizing reaction at the surface of the material. The behavior of the materials was assessed by Slow Strain rate testing (SSRT), C-Ring Sulphide stress cracking and Crevice corrosion test, conducted on UNS N06985. Grades sourced from three (3) distinct manufacturers were tested to evaluate different manufacturing systems (routes) and levels of cold work, which are known to be critical in the performace of the cold worked CRA materials. Although, CRAs have a greater CAPEX due to the content of costly chemical elements: Chromium, Nickel, Molybdenum, etc, they may be cost effective in a life cycle cost analysis as they will prevent workovers, assure a higher HSE and well integrity level.