TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe sulfide stress cracking resistance of steel oil country tubular goods (OCTG) is commonly correlated to the hydrogen sulfide (H 2 S) partial pressure, calculated by multiplying the mole fraction H 2 S by the total system pressure. However, sour gas mixtures exhibit non-ideal behaviors at high system pressure. Neglecting these non-ideal effects causes large over-conservatism at total system pressures above 5000 psi. It is important to compensate for non-ideal gas and solution behaviors in order to select representative laboratory test environments for sour service fit-for-purpose materials evaluations.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe ability to optimize the use of carbon steel in corrosive service presents many economic advantages, including minimizing the use of expensive corrosion resistant alloys, reducing well count by enabling optimized large bore completions, and eliminating additional offshore pipelines and facilities. An integrated approach to corrosion modeling and testing is employed by ExxonMobil to reliably extend the application of carbon steel.The integrated approach to predicting corrosion has five primary elements:1. Rigorously establish the environmental conditions by conducting thermodynamic and compositional hydraulic analyses, and characterize how these conditions are expected to change over time. 2. Identify the local environmental conditions and the types of corrosion that are expected to occur (e.g., weight loss, pitting, environmental cracking), including sensitivity and upset cases. 3. Conduct realistic corrosion tests under the identified field conditions by simulating brine chemistry, dissolved acid gas concentrations, hydrocarbon effects, fluid shear stresses, and flow regime in appropriate laboratory equipment. Specialized laboratory test apparati, such as a large-diameter sour, multiphase flow loop and large-volume highpressure high temperature autoclave test cells, have been designed and constructed to ensure proper reproduction of field conditions. 4. Mathematically extrapolate the results of the laboratory tests to the field, enabling calculation of expected tubular life. 5. Conduct life cycle cost analysis. This paper will describe how this integrated approach to predicting corrosion is used to evaluate the use of carbon steel in oil and gas production environments. Special emphasis will be placed on the prediction of pitting corrosion in H 2 Scontaining environments.

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The ability to optimise the use of carbon steel in sour service presents man y economic advantages, including minimizing the use of expensive corr osion resistant alloys, enabling optimised large bore completions, and eliminating addit ional offshore facilities. An integ rated approach to corrosion modeling and testing has been d eveloped to reliably extend the ap plication of carbon steel. Key elements of this integrated approach include: (1) ri gorously establish tubular environmental conditions, (2) accurately simulate environmental conditions (acid gas concentratio ns (CO 2 /H 2 S), water c ut, and water composition) in the laboratory, (3) mathematically extrapolate laboratory weight loss and pitting to predict tubing life, and (4) validate tubing life predictions with field caliper data. This paper describes the application of the inte grated approach to evaluate L80 tu bular corrosion and predict tubing life for a range of a cid gas (CO 2 /H 2 S) concentrations. The pape r also discusses the corrosion mechanisms and validation of predicted corrosion with field caliper data.