Abstract

The major gaseous impurities in the subquality natural gas sources are acidic components, such as hydrogen sulfide and carbon dioxide. Considering that H2S easily dissociates into hydrogen and elemental sulfur, thermodynamic properties and specially phase equilibria of liquid and gaseous systems containing hydrogen, hydrogen sulfide, carbon dioxide, other acidic components, and light hydrocarbons are of much interest to the natural gas and gas condensate production industries.

In this paper we report the development of a simple and accurate cubic equation of state for prediction of thermodynamic properties and phase behavior of sour natural gas and liquid mixtures. This cubic equation of state, which is based on statistical mechanical theoretical grounds, is applied to pure fluids as well as mixtures with quite accurate results. All the thermodynamic property relations of sour gaseous and liquid mixtures are derived and reported in this report. Parameters of this equation of state are derived for different components of sour natural gas systems. The resulting equation of state is tested for phase behavior and other thermodynamic properties of simulated and natural sour gas mixtures. It is shown that the present equation of state, even though it is simple, predicts the properties of interest with ease and accuracy.

Introduction

In the past two decades, a number of subquality natural gas/gas condensate fields have been discovered around the world. The major impurities of these subquality natural gas/gas condensate sources consist of N2, CO2 and H2S. since that H2S easily dissociates into hydrogen and elemental sulfur therefore, thermodynamic properties and specially phase equilibria of liquid and gaseous systems containing hydrogen, hydrogen sulfide, carbon dioxide, other acidic components, and light hydrocarbons are of much interest to the natural gas and gas condensate production industries.

Transportation, and processing of sour and hydrogen containing natural gas is of major concern to the industries involved. Carbon dioxide and hydrogen sulfide are considered as being impurities in natural gas and oil and are responsible for corrosion of the flow-line and processing equipment. Separation of these gases from natural gas and oil is usually the most expensive part of natural gas and oil treatment processes. The economical importance of treatment of sour gas has made it important for the gas and oil industry to have accurate equation of state to represent properties of sour gases and liquid mixtures. Presence of sour gases in crude oil could also cause deposition of heavy organics, such as asphaltene and wax, from oil which would plug the well, pipeline and refining equipment.

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