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.

In recent years, oil and gas operators have faced new challenges regarding the resistance of sour service 110ksi specified minimum yield strength material in extreme sour conditions, meaning partial pressures of H2S higher than 15psi (1bar). Furthermore, high pressure wells in presence of H2S such as deepwater and HPHT require high strength 140ksi specified minimum yield strength carbon steel, for which even at high temperature can develop sulfide stress cracking. This paper describes a methodology to select and qualify materials for such critical conditions, taking into account the aspects from material design to specific laboratory testing to provide suitable material for the well environment. The results presented highlight the importance of material qualification in the well design phase prior to product application. A few well architecture examples are presented, explaining the benefits of using qualified materials with high mechanical properties and improved sulfide stress cracking resistance, opening the doors of new oil and gas field explorations with profitable solutions.

The limit of Sour Service (SS) grades regarding Sulfide Stress Cracking (SSC) resistance is defined by ANSI NACE MR0175 / ISO 15156 standard. For instance, API T95 grade is acceptable to be used in all regions of environmental severity and for all temperatures. As per Annex B of the same standard, SSC laboratory testing in accordance with NACE TM0177 Methods A and D in Solution A saturated by 1 bar H2S partial pressure (PH2S) qualify a material for all SSC regions, up to 10 bar PH2S. To evaluate this statement and verify if the existing NACE guidelines apply also for SS 110 ksi Specified Minimum Yield Strength (SMYS), a procedure to assess the SSC resistance in high H2S pressure was developed. This procedure was applied to enhanced SS 95 ksi and 110 ksi SMYS materials. The methodology consists in regular purging and filling of the gas phase in order to keep constant the PH2S and to remove hydrogen gas produced by generalized corrosion. Investigations combined NACE TM0177 Method A and D tests, characterizations of the iron sulfide scales and hydrogen electrochemical permeations. This methodology enables to give some insights on the corrosion mechanism and the influence of high partial pressure of H2S on the SSC resistance.

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In recent years, Oil and Gas operators have faced new challenges with higher H2S partial pressure wells, especially in the Middle East. NACE MR 0175 part III provides guidance on the material selection for Corrosion Resistant Alloys; however, the well conditions considered by the Operator (total pressure 5526 psi, 1044 psi H2S, 279°F) are on the border of the UNS N08028 / UNS N08825 application domain, and therefore the recommendation would be to use a higher alloy, UNS N06985 material. This paper describes a methodology to perform fine material selection for such critical conditions considering the representativeness of the testing condition and specific laboratory testing to qualify a suitable material for the intended application. The objective was to evaluate the suitability of UNS N08028 and UNS N08825 material 110 ksi in the conditions described above. Based on actual reservoir conditions and fluid analysis, the test solution was defined to represent actual corrosiveness of the environment. Solution components, gas phases and in situ pH were defined using OLI® Stream Analyzer Thermodynamic software to reach the specified conditions at the test temperatures. Then, Stress Corrosion Cracking was assessed based on SSRT (Slow Strain Rate Test) as per NACE TM 0198-2016 [9], a rather conservative test as the material is stressed in its plastic domain; and C-ring as per NACE TM 0177-2016 [12], performed on rolled material to be representative of the final material surface finish. All SSRT specimens showed a high ductility ratio and the absence of secondary cracking on the gauge section on both grades. All SCC C-ring specimens exposed to the environment successfully completed 720 hours exposure on both grades. Both UNS N08028 and UNS N08825 materials successfully passed the SSRT and C-ring tests, allowing the Operator to optimize the material selection by choosing a grade specifically qualified for their application and reducing the overall tubular cost by 30%.