No abstract

Super 13Cr (S13Cr) 110ksi Specified Minimum Yield Strength (SMYS) grade, which was already supplied for previous High Pressure High Temperature (HPHT) sweet and sour gas fields, was considered for a new HPHT sweet and sour gas exploration field. After analysis, the new reservoir conditions were close to the limit of the application domain previously validated using the most stringent testing requirements, as defined in annex B of NACE MR0175/ISO 15156-3 standard. Under these circumstances, a natural switch to duplex stainless steel (22-5-3) material is usually recommended, leading to significant impact on project cost and lead-time. This paper describes the work done between Oil Country Tubular Goods (OCTG) supplier and operator to define specific test condition based on the new reservoir environment and tubing loads. In order to qualify the material, a complete testing program was undertaken to assess Sulfide Stress Cracking (SSC), Stress Corrosion Cracking (SCC) and mass loss resistance. In total four scenarios have been considered and analysed: shut-in and flowing conditions at both the well head and downhole locations. For these scenarios the representative applied stresses as well as reservoir fluid composition were defined. SSC test was performed to verify the product suitability. The results showed that the material failed when using the most stringent requirements. However, when tested at specific well condition the material successfully passed the entire qualification. Additionally, deeper SSC investigations were carried out in order to understand the influence of each parameter between initial and specific test condition, such as H2S partial pressure (ppH2S), chloride content, applied stress and material chemistry. The benefit of this approach was to demonstrate to the operator that S13Cr was validated for the conditions of the new reservoir; thereby reducing lead time and by half the cost of purchasing duplex material during material selection phase. Generally, this methodology could be applied to all well environments requiring stainless steel materials.