51313-02843-Improving pH Prediction for High Pressure and Temperature Applications in Oil and Gas Production

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Product Number: 51313-02843-SG

ISBN: 02843 2013 CP

Author: Jean Kittel

Publication Date: 2013

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pH prediction represents a crucial step before selecting materials for use in sour oil and gas wells as regards weight loss corrosion and H2S cracking. Among the numerous parameters which determine the equilibrium pH important ones are CO2 and H2S partial pressures (PCO2 and PH2S respectively) the total pressure the ionic strength and the chemical composition of the solution and the temperature. Most models used by oil and gas operators present a too narrow range of validity for these parameters which makes them inappropriate for high pressure and high temperature (HPHT) fields or for CO2 reinjection. This paper presents modeling improvements which allows extending the prediction validity in temperature and pressure to respectively 200-250°C and above 200 bar of acid gases and for an ionic strength up to 5 mol.kg-1.
The new model takes into account the fugacities in gas phase of CO2 and H2S. The influence of water and CH4 pressure is also taken into account up to several hundred bars.
After verification of the model calculation by comparison with experimental measurements of pH under high pressure and other published models the impact of pH calculation for HPHT applications is discussed. In particular it is shown that high pressure of CH4 in the gas phase modifies the prediction by several tens of pH unit.