Best Practices for Design, Operation, and Maintenance of Wireline Intervention Tools for Sour Service

Abstract

This paper presents lessons learned from the design and field deployment of many different assets in sour environments. It will address the requirements and implications of design, operation, and maintenance of wireline intervention tools when exposed to H2S and CO2. Many wells in the world are drilled in fields with high concentrations of H2S and CO2. Even low concentrations of H2S put wireline tools designed from conventional downhole materials at risk of catastrophic failure through sulfide stress cracking (SSC), stress corrosion cracking (SCC), and hydrogen induced cracking (HIC). These wells are also highly corrosive, so even materials that are not highly vulnerable to these failure modes may suffer from extensive corrosion that still renders them unusable in these environments. Wireline intervention tools are at especially high risk of failure because the high loads they experience during normal operations preclude practices that might be standard in lighter-duty equipment like wireline logging tools. Wireline intervention tools that are intended for sour service should be designed from the beginning with corresponding requirements to avoid not only SSC, SCC, HE, and corrosion issues, but also any issues that may be related to the materials that are selected to avoid these failure modes. Materials capable of supporting high tensile forces in sour environments are extremely limited, and most of these are susceptible to galling. Care must be taken during the design to avoid situations where this galling would occur. Both H2S and CO2 are soluble in water to create weak acids, so the amount of water present is also an important factor when determining acceptable materials. Operation of wireline intervention tools in sour service environments must be carefully planned and executed. Proper cleaning and maintenance procedures are also critical to maintaining tool reliability and longevity following sour operations. Much historical wireline intervention design and material selection is based on tribal knowledge (i.e., unwritten knowledge and best practices). and standard ANSI/NACE MR0175/ISO 15156, Petroleum, Petrochemical and Natural Gas Industries—Materials for use in H2S-Containing Environments in Oil and Gas Production. Tribal knowledge is often suspect, and the application of the standard is difficult for wireline intervention equipment because factors other than cracking are important. This paper also moves beyond material selection to include guidance and best practices for mechanical design, operation, and maintenance of wireline intervention tools that are not directly addressed by NACE standards.