Predicting Water Content of Sweet Natural Gas – Hydrate Systems

Abstract

Abstract Water content measurement and prediction can be very challenging at conditions of low temperatures and high pressures (hydrate conditions). As a result, many correlations for natural gas water content determination either cannot predict water content of natural gas at these conditions or, have a low accuracy of prediction when they do. In this study, nomographic data generated with the Cubic Plus Association (CPA) equation of state with pressure range of 50 to 500 Bar and temperature range of -20 to 20 °C was used in developing a simple, easy to use correlation with a single predictor (Temperature) variable. This correlation was validated with experimental data obtained from a high pressure variable volume hydrate cell with an analyser based on the Tuneable Diode Laser Absorption Spectroscopy (TDLAS) technology and compared with six (6) other correlations for predicting water content at these conditions. The average absolute deviation (AAD) for the correlations showed that the model in this study had the least AAD of 21 and 5 at 50 and 75 bar respectively. The Behr's correlation had the least AAD of 5 and 10 at 150 and 200 bar respectively, closely followed by the model in this study with AAD's of 9 and 13 respectively. While the Moshfeghian and Sloan correlations gave fairly accurate predictions with maximum AAD's of 36 and 32 respectively, the Kazim and Ning correlations performed poorly with AAD's of 50 and 44 respectively.