f Prediction of Temperature Change of Hydrocarbon Gases Using A Two- Parameter Z-Factor Correlation Under Isenthalpic Flash Conditions

Isenthalpic expansion processes of real gases through restrictions are usually accompanied by a temperature change of the gas phase. This phenomena is known as the Joule-Thomson cooling (or heating). The temperature change depends on the initial and final pressures and initial temperature as well as the composition of the gas phase. Natural gases cool down at moderate pressures upon expansion in downhole perforations or in surface chokes whereas gas condensates may heat up when expanded at elevated reservoir pressures and temperatures. The direction and the magnitude of the temperature change may be predicted by using an isenthalpic flash calculation procedure. The constant enthalpy expansion of a real gas may result with condensation of a liquid phase due to the lowered gas temperature. In such processes, simultaneous solution of mass and enthalpy balance equations is required. If there is no liquid condensation after the expansion, the enthalpy balance equation should be solved for downstream temperature given up and downstream pressures and upstream temperature. An equation of state or a two-parameter z-factor correlation can be used to model the PVT behavior of the single phase natural gas in constant enthalpy flash calculations. Two-parameter z factor correlations are simpler to code and reduce computational time. However their accuracy in energetic computations is not well understood. In this paper, predictive capability of Abu Kassem-Dranchuk z-factor correlation is studied when used in calculating temperature changes during a constant enthalpy flash process. The results are compared to Peng-Robinson equation of state and to a leading reference thermodynamic fluid properties program results.