Oil‐Grade Alloy 718 in Oil Field Drilling Applications

Abstract

Due to continuous advancements in drilling technology, the materials in use have to fulfill higher demands in regards to mechanical properties and corrosion resistance. The complex working loads and high vibration, the hostile downhole environments, together with the high working temperature and pressure encountered when operating in an ultra deep drilling environment, provide major challenges for the drilling tool materials. This paper focuses on the performance of oil-grade alloy 718 for applications in bottom hole assemblies (BHAs) under drilling conditions. Potentiodynamic polarization was applied to investigate the general characteristics of corrosion and pitting attack. Key influence factors including working temperature, cation species in corrosive medium, and post-mortem heat treatment were discussed. These results will help to direct the optimization strategy of Ni-base superalloys in oil field drilling. Overview Of Oil Grade Alloy 718 in Drilling Alloy 718 was invented more than 50 years ago but has been used in the oilfield for drilling tools for approximately the last 20 years. This is related to the fact that the demand for expensive, high strength, corrosion resistant oil grade materials was emerging in the 1990s with the development of expensive modules as part of the bottom hole assembly (BHA). A BHA normally includes modules used for logging while drilling (LWD), and measurement while drilling (MWD). Figure 1 shows the sketch of drill pipe together with the BHA and drill bit. Figure 1 Drill string with 1= drill pipe, 2= bottom hole assembly (BHA), and 3= drill bit