Extending Sour Service Limits for Nickel-Based OCTG Alloys in High-Temperature High-Pressure Wells: an Enhanced Guide for Safe Application

Abstract As traditional oil and gas resources dwindle, exploration must target new reservoirs that exhibit increasingly higher temperatures and sourness, posing significant challenges for downhole material selection according to NACE MR0175/ISO 15156. Annex A of this standard has proven to be potentially conservative, significantly limiting material options in these harsher conditions, and the fit-for-purpose tests for each well are time-consuming and expensive. To address this issue, systematic tests following NACE TM0316 and TM0198 were conducted on N08028 and N06985, two Ni alloy grades commonly used in OCTG tubular applications. A new boundary line of temperature vs. H2S partial pressure was established, significantly extending the limits of Annex A of ISO 15156. Field test results following this new guideline will also be provided to demonstrate its effectiveness. This new boundary allows for safe material selection in new field conditions without the need for costly and time-consuming fit-for-purpose tests.