American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

Abstract

Sulfide stress cracking (SSC) is a major obstacle to the successful drilling and completion of deep wells in sulfide environments. The mechanism of SSC is described and the current status of SSC resistant steels is reported. Precautionary measures to avoid or control SSC are enumerated.

Introduction

A major obstacle to the successful drilling and completion of deep wells is the increasing frequency of sour environments as deeper horizons are penetrated. While sour environments can cause trouble at any depth, higher strength steels required for deep drilling are more susceptible to failure than steels normally used for shallow wells and the deeper environments may be even more hostile.

The sudden catastrophic failure mode experienced in sour environments is termed sulfide stress cracking (SSC), and is characterized by flat, brittle failures with little visible corrosion and no detectable plastic deformation. These failures occur plastic deformation. These failures occur while operating at apparently safe load levels and often after extended periods of satisfactory performance.

In the 20 to 25 years since the epidemic of drillstem failures in the Jumping Pound and Pincher Creek fields in Canada and Pound and Pincher Creek fields in Canada and the Lacq field in France focused attention on material performance in sour environments, extensive investigations have conclusively shown that SSC is a severe form of internal hydrogen embrittlement, accentuated by the presence of hydrogen sulfide (H2S). presence of hydrogen sulfide (H2S).

MECHANISM OF SULFIDE STRESS CRACKING

Atomic hydrogen (H), generated in drilling fluids by corrosion processes, bacterial action, or thermal degradation of organic additives, can be absorbed into and diffuse through the steel crystal lattice. In the absence of H2S, atomic hydrogen quickly forms molecular hydrogen (H2) that cannot be absorbed. The presence of H2S greatly decreases the speed of recombination of H to H2, thereby increasing the amount of atomic hydrogen available for absorption.

After being absorbed into the steel, the atomic hydrogen migrates to and accumulates at the region of highest stress usually just below the root of a thread, notch, section change, or other discontinuity.

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