High Strength Low Alloy Steel for HPHT Wells

Abstract

Carbon OCTG selection for HPHT wells has become a very challenging task for well design engineers, due to combination of high pressure with H2S requiring the use of high strength material to achieve the required safety factors avoiding Sulphide Stress Cracking (SSC) at the same time. This requirement prompted a study based on proprietary laboratory testing data in correlation with existing normative systems (API 5C3 and NACE 15156) for selection of high yield strength material in H2S HPHT wells. With the information provided, the design engineer could better link existing normative systems with proprietary testing to define the best applicable window of high strength material in H2S wells for HPHT environments. The paper summarizes the public studies done so far by the industry for the material selection of carbon OCTG for HPHT wells comparing with typical ISO 15156 guidelines. Detail explanations of the characteristics of each testing method are also included; the paper also contains additional study of high strength Sour Service material under different testing conditions to define the Sulphide Stress Cracking (SSC) behavior compared to ISO 15156 material selection guidelines. Two steel grades were tested: Sour Service 110ksi and Sour Service 125ksi, the SSC limits were defined using NACE TM0177 Tensile Tests and DCB Tests. The paper intends to provide supplementary guidelines to help the well design engineer on the material selection process by expanding API 5C3 fracture mechanics formulas and concepts to address H2S selection concepts, explanation of NACE 15156 for high strength materials for Region 1–2–3, and clarification of different methods used to test materials with H2S as per NACE 15156.