This is a collaborative R&D project supported by GERG, the European Gas Research Group (http://www.gerg.eu), aiming to evaluate and compare carefully selected thermodynamic models used for calculating dew points of natural gas mixtures containing water and/or production chemicals.
Participants are Statoil (Norway), GASSCO (Norway), Open Grid Europe (Germany), DGC (Denmark), Snam Rete Gas (Italy) and CERE / DTU (academic partner).
The water content of natural gas often poses problems during the production, transmission and distribution of the gas. Small quantities of undesired dissolved water may condense leading to the formation of condensed water, hydrates and/or ice. Such condensed phases may result in corrosion, two-phase flow problems, safety hazards and flow assurance issues, slugging of the flow lines, valves and instrumentation resulting in reduced capacity and shutdowns, and reduction of the oil recovery efficiency because of reduction of the reservoir permeability. Accurate thermodynamic models able to calculate the water vapor concentration in equilibrium with hydrate, ice and water in natural gas at pipeline operating conditions (253-323K and up to 250bar) are necessary both because experimental data are limited and difficult to obtain, and because the limits of dehydration techniques (physical adsorption and condensation) need to be defined. The latter techniques use chemicals (eg. glycols and alcohols) which also condensate, adding one more level of modeling challenge.
The main purpose of this project is to evaluate and compare the performance of the CPA (Cubic-Plus-Association) equation of state (EoS) and GERG-water calculation method (an ISO-standard model specifically designed to correlate water content and dew points of natural gas) regarding the calculation of dew points of natural gas systems containing water and traces of selected production chemicals.
In parallel, databases of reliable experimental data will be developed and used to establish and suggest model parameters / modifications, different data analyses will be performed and a user-friendly software for calculation of dew points will be developed and disseminated to the participating companies.
Other deliverables include publications, technical reports and presentations. Finally, the results will be presented in progress meetings held twice per year. The kick-off meeting took place in December 2011.