Produced petroleum fluids containing hydrogen sulfide (H2S) Produced petroleum fluids containing hydrogen sulfide (H2S) gas are often referred to as "sour". Hydrogen sulfide gas in the presence of free water can cause certain metal alloys to crack which is referred to as Sulfide Stress Cracking (SSC). SSC of metals is a serious safety issue for the petroleum industry and is addressed by the NACE (National petroleum industry and is addressed by the NACE (National Association of Corrosion Engineers) MR-01-75 document which establishes requirements for metallic materials suitable for sour environments. Sour service materials selection is a complex problem often facing personnel not experts in this area.
Since SSC and the NACE MR-01-75 document are not easily understood by most petroleum engineers, an expert advisor computer program was developed to integrate expert comments, SSC fundamentals, key metallurgy concepts, and NACE MR-01-75 requirements. This program is termed an expert advisor rather than an expert system because it seeks to teach the knowledge rather than simply provide expert answers. A novice user is able to proceed through a structured tutorial to establish the necessary fundamentals on metallurgy, SSC technology, and NACE MR-01-75 requirements necessary for informed use of the NACE document. More experienced users can proceed directly to the expert system portions of the system for direct evaluation of an alloy specification. A general survey option is available within the expert system portion to evaluate NACE requirements in a general context without being limited to the specifics of a given alloy specification. This software demonstrates that expert systems technology can be applied to SSC and NACE MR-01-75 to provide expert communication to users.
The National Association of Corrosion Engineers NACE MR-01-75 document was developed as guideline to assist in the selection of alloys that are suitable for sour service as well as manufacturing requirements including heat treatment and cold working. The NACE MR-01-75 document is limited in scope. The focus of this document is on applications where safety is an issue if pressure containment is compromised.
The NACE document assumes the user has a good understanding of the complex relationship between the environment and metallurgy. Petroleum engineers often do not have the necessary metallurgical background to make informed decisions about materials selection in cases where sour service is involved. An example is the relationship between heat treatment procedures, residual stresses, and SSC susceptibility. An expert system software package has been developed to bridge this "knowledge gap". This expert system differs from the traditional expert system since the approach has been to educate and to assist the user in making an informed decision. The software does not simply interrogate the user and supply a single answer. Novice users are able to learn metallurgical terminology and complex relationship between the environment, manufacturing requirements, and alloy selection. For the expert, the tutorial part of the program can be bypassed and the user is provided a systematic checklist in the materials selection process.