Important reserves of oil and gas, which are left to be discovered and produced, are mainly concentrated in challenging locations and under severe conditions [i.e., high pressure (HP)/high temperature (HT)]. The HP/HT plus the presence of aggressive environments mean a highly demanding scenario for tubes used in producing oil and gas [oil country tubular goods (OCTG)]. Material property requirements include high mechanical properties at ambient and high temperatures (e.g., as high up to 200–250°C). Additionally, if H2S is present, resistance to sulfide stress cracking may be required, depending also on other environmental conditions. Even without H2S, contents of CO2, chlorides, and high temperatures and pressures can represent a risk of high corrosion rates. The improvement of some of the required properties of the materials (e.g., steels) can mean the impairment of other properties. Consequently, a careful balance is required and limits exist for the individual modification of the properties. The present article focuses on the two main environmental deterioration problems in the oil and gas business: (I) sulfide stress cracking and (II) CO2 corrosion. A description of the acting mechanisms and the effect of environmental and material factors are presented. Selection criteria and current material limitations are also discussed.
Significant recoverable reserves of oil and gas left to be discovered and produced are mainly concentrated in challenge locations, such as deep-water offshore, remote arctic locations, and difficult-to-manage reservoirs with unconsolidated sands. Additionally, aggressive environments (i.e., high H2S and/or CO2 contents) with high pressures and high temperatures are conditions to be faced by materials in many wells.
Materials and corrosion control technologies to be used under such demanding conditions and locations must be highly reliable due to the excessive cost of replacement or failure in these difficult-to-access locations.
The main concerns for downhole tubulars from the related corrosion problematic point of view are environmental cracking and uniform or localized corrosion.
The total annual cost of corrosion in the oil and gas production industry is estimated to be US$1,372 billion, broken down into $589 million in surface pipeline and facility costs, $463 million annually in downhole tubing expenses, and another $320 million in capital expenditures related to corrosion.1 It is widely recognized within the oil and gas industry that effective management of corrosion will contribute toward not only cost reduction but also compliance with safety, health, and environmental policies.
