Performance of Equation-of-State for Hydrocarbon Dew Point Control in Gas Flow-line in a Nigerian Field

Abstract

Associated gas in a flow-line in a Nigerian field was suspected to be accountable for unaccounted-for gas in the flow-station. Gas molecular compositions of Low Pressure suction gas and Injection Discharge gas for operating conditions of pressure and temperature from the field were analysed by the use of Soave-Redlich Kwong and Peng-Robinson Equations of State with PVTp thermodynamic software. The phase envelope predicted the Hydrocarbon dew point(s) observable from the dew point curve, and the operating conditions of 116^oF for LP suction gas and 112.8^oF for Injection Discharge gas were observed to be outside of the dew point curve, and greater than the cricondentherm of 69.2^oF and 66.6^oF for SRK EOS and 65.6^oF and 63.0^oF for PR EOS respectively as predicted by the PVTp. The conditions made it impossible for hydrocarbon liquid dropout, hence, could not account for the gas. Hydrate formation was also prevented as observed from the hydrate curve.

Keywords: Cricondentherm, Dew Point System, Equation of State, Natural gas