Phase Equilibria Studies Relevant to Natural Gas Subsea Processing
Experimental VLLE studies for Natural Gas related mixtures
Abstract
Studies on natural gas subsea processing are becoming important with regard to the necessity of ensuring the untroubled and uninterrupted natural gas recovery in the North Sea.
The changes in pressure and temperature from reservoir conditions to the conditions which are optimal for subsea processing can constitute a problem because of the formation of solids and in particular gas hydrates. Generally, the range of interest is often very broad and include high pressures up to 200 bar (or higher in some fields) and also low temperatures down to 0 °C or even lower in some cases (during depressurization).
Therefore, robust design and operation in future subsea developments requires new experimental thermodynamic data, detailed understanding and prediction of the thermodynamic properties of reservoir fluids over a broad temperature and pressure range.
The present work constitutes a subpart of the greater research project entitled “Thermodynamics of Petroleum Fluids Relevant to Subsea Processing”. This work deals with the phase equilibrium of systems containing both polar and non-polar components in two ways.
In terms of experimental work, the purpose is to examine the Vapor-Liquid-(Liquid) phase Equilibria (VL(L)E) of well-defined binary and ternary mixtures related to natural gas fluids, with the presence of thermodynamic gas hydrate inhibitors. In particular, the components contained in the mixtures include methane, water, n-alkanes and production chemicals.
The mixtures of interest are introduced into a high-pressure cell to the desired conditions and when equilibrium is reached compositional measurements are conducted with the use of a GC.
In the framework of this project, the experimental set-up has been rebuilt. Therefore, at first, it has been investigated the VLE of two reference mixtures (methane/water and methane/n-hexane) and in this way, ensure that the experimental apparatus and the procedures introduced are appropriate.
Subsequently the VLLE of two ternary mixtures (methane/n-hexane/water & methane/n-heptane/water) was investigated.