Sour Service Fracture Toughness from Lab-Scale to Full-Scale: An Overview of the Impact of Test Parameters and How They Link with the Cracking Mechanism

Unconventional wells are well known to be cost driven and require cost-effective material due to the shorter production cycle after hydraulic fracking than conventional developments. As many of ADNOC gas discoveries are deep carbonate reservoirs and inherently sour, Sulfide Stress Cracking (SSC) risk must be considered during completion design. The integration of fracture mechanics into that process requires the determination of an accurate measure of the fracture toughness against SSC, e.g. K_ISSC, such that the risk of burst can be predicted and avoided more accurately in the field. This paper reminds the learnings from previous attempts for correlating burst pressure obtained in full-scale tests with fracture mechanics outputs from small-scale sour tests. The most used and relevant fracture mechanics tests employed on high strength OCTG steels in sour environments are described in a second part. A third part is dedicated to the review of the most important parameters affecting the measurement of the SSC fracture toughness. Followed a discussion on the reason why a crack arrest test like NACE TM0177 DCB test provides higher K_ISSC than a crack start test like a constant load SENT test.