Prediction of the Potential Hydrocarbon Liquid Content of Lean Natural Gas Comparison with Field Tests

摘要

The objective of this study is to design a model which allows to predict at specified temperature and pressure the amount of liquid formed in pipelines transporting lean natural gas (potential hydrocarbon liquid content). The only input information that is used is an extensive gas chromatographic analysis of natural gas, which was recently developed by N. V. Nederlandse Gasunie. The availability of such a model is of great importance for the natural gas industry because the formation of liquid during storage, transport and processing needs to be anticipated. In order to achieve our objectives a two stage project has been proposed. At the first part, new highly accurate solubility data of heavy hydrocarbons in some of the main constituents of natural gas like methane and nitrogen have been measured. Also an attempt has been made to simulate the behaviour of real natural gas by performing solubility measurements of heavy hydrocarbons in mixtures of methane, nitrogen, carbon dioxide and ethane. Based on the information and experience gained at the first part, the next step was the modelling of real natural gas. For this purpose the Peng-Robinson equation of state was selected and applied with interaction parameters optimized at conditions of practical interest, i.e. at pressures 9 < p/bar < 67 and at temperatures 250 < T/K < 290. Prom a sensitivity analysis it could be concluded that the Potential Hydrocarbon Liquid Content (PHLC) is mainly influenced by the concentration and characterization of C_7-C_(12) fractions. In this work the PHLC deriving from two different characterization procedures to represent these fractions are compared with experimental PHLC of real natural gas measured by Gasunie.