Patent ID: 7010433

Claim:
A method of determining the diluent concentrations in a natural gas, comprising the steps of: storing a database representing a number of reference natural gas mixtures whose molecular weights and carbon dioxide and nitrogen concentrations are known; modeling the molecular weight of a gas mixture as a function of the speed of sound in the gas mixture, the carbon dioxide concentration, the nitrogen concentration, and a set of constant values, thereby obtaining a model equation; at a first temperature and pressure state of the gas mixture: measuring the speed of sound in the gas mixture, determining the constant values for the gas mixture from the database, and substituting these values into the model equation, thereby obtaining a first equation for the molecular weight of the gas; at a second temperature and pressure state of the gas mixture: measuring the speed of sound in the gas mixture, determining the constant values for the gas mixture from the database, and substituting these values into the model equation, thereby obtaining a second equation for the molecular weight of the gas; at a third temperature and pressure state of the gas mixture: measuring the speed of sound in the gas mixture, determining the constant values for the gas mixture from the database, and substituting these values into the model equation, thereby obtaining a third equation for the molecular weight of the gas; and solving the three equations for the diluent concentrations of the gas.