Optimizing Sour Gas Qualification Testing: Determination and Verification of H2S Solubility from H2S/N2 Gas Mixtures up to 20,000 psig at 70°F

Traditionally, the H2S partial pressure (PH2S) of gas/hydrocarbon phase has been used as primary sour severity metric for material qualification and selection under ANSI/AMPP (NACE) MR0175/ISO 15156 guidelines. While PH2S is appropriate characterizing low total systems, strict, or ideal, Henry’s Law approach leads to over estimation dissolved concentration (CH2S) high-pressure, high-temperature (HPHT) wells by up approximately 20 times at 70°F (21°C). Alternatively, Ensemble equation corrects non-ideal behavior HPHT conditions avoids over-estimation CH2S. Given industry’s reliance on using thermodynamic models evaluate an investigation was initiated determine accuracy these model calculations. An empirical program undertaken verify CH2S predictions H2S-N2-H2O system. Multiple 2.7 L C-276 lined autoclaves were charged with a fixed inventory in N2 multiple steps, increasing pressure, between 30 psig 20,000 (3 bar 1,380 bar) 70±5°F (21±3°C). Per step, levels both headspace gas liquid phases measured common sampling techniques (H2S-specific colorimetric tubes iodometric titration, respectively), following ANSI/NACE TM0177-2016 The results calculate corrected (apparent) solubility coefficients (AkH2S). Very good agreement observed empirically computationally derived AkH2S values.