Puguang region is known for containing sour fields with significant amount of H2S. Since 1975, sour service wells have been drilled entailing critical drilling conditions. To optimize drilling efficiency without sacrificing security, drill string improvements have been always looked for, by carefully evaluating steel grades, drill pipe sizes and connections.
The evolution of drilling programs has driven the industry to develop more suitable solutions adapted to extreme and aggressive conditions such as Sour Service environments. High strength drill pipe is often necessary to achieve deeper drilling performance, even when Sulfide Stress Cracking susceptibility is observed in minimal concentrations of H2S in partial pressures. Due to the astringency of the sour environment, particular precautions have to be defined to select and characterize an adapted Sour Service steel grade.
This paper presents the evolution of choices in drill string design from basic API grades and connections to adapt and proprietary steel grades resistant to H2S with a high mechanical performance properties and high torque double shoulder connections.