Increased Tool Life and Enhanced Reliability for Bottomhole Assemblies in Harsh Environments

Abstract

Non-magnetic collars must be strong, tough, and corrosion resistant to withstand dynamic drillstring loads while also providing robust housings for measuring and logging-while-drilling (MWD/LWD) tool electronics. This paper describes a materials solution to problems related to the corrosion of drill collars in hostile well conditions. Typical nitrogen-strengthened chrome-manganese drill collar alloys are at risk of early retirement or downhole failure due to pitting, stress corrosion cracking (SCC), and sulfide stress cracking (SSC). Tool non-productive time due to increased maintenance, repair, overhaul frequency, and premature removal from service increases operating costs. The results of laboratory trials in conditions representative of active drilling basins show the differentiated performance of a chrome-nickel stainless steel and nickel-based alloy 718 relative to more common chrome-manganese stainless grades currently in wide-spread use. The pitting resistance, SCC resistance, and SSC resistance of both chrome-nickel stainless and nickel grade were found to be significantly better under wide ranging conditions and confirmed the capacity of both alloy systems to outlast incumbent drill collar grades.