Selecting Representative Laboratory Test Conditions for Mildly Sour Sulfide Stress Corrosion (SSC) Testing

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Product Number: 51314-4243-SG

ISBN: 4243 2014 CP

Author: Amit Kumar

Publication Date: 2014

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Dissolved H2S in the produced fluid degrades the performance of oil country tubular goods (OCTG) steels by leading to sulfide stress cracking (SSC). Direct material evaluation or fit-for service (FFS) testing at high reservoir pressure is challenging. Alternative is to reproduce appropriate dissolved hydrogen sulfide (H2S) level to perform tests in lab at lower pressures. In general oil and gas (O&G) industry uses partial pressure of H2S to define the FFS test conditions. However sour gas mixtures exhibit non-ideal behaviors at high system pressure. Neglecting these non-ideal effects causes large over-conservatism at high reservoir pressures for mildly sour conditions. It is important to compensate for non-ideal gas and solution behaviors in order to select representative laboratory test environments for FFS materials evaluations. Currently there are no specific guidelines on selection of H2S levels to represent mild sour environment for testing at ambient pressure.In this work a thermodynamic model has been developed to predict the solubility of H2S at high pressure. Model has been used to predict equivalent representative laboratory conditions for mild sour conditions at high reservoir pressures. This approach ensures that the proper concentrations of H2S are dissolved into the test solution. Results on validation of model predictions using double-cantilever-beam (DCB) tests for various H2S levels are also presented.Keywords: Sulfide stress cracking fit-for-service mild sour H2S solubility.