Phase behaviour modelling of systems containing gas hydrates and asphaltenes
Gas hydrates are crystalline compounds formed from a combination of water molecules
with suitably sized non-polar or slightly polar molecules under certain conditions of
temperature and pressure. They are well known for their role in the blockage of subsea
pipelines and oil and gas production / processing facilities, which is a major concern for
the petroleum industry. On the other hand, asphaltenes are the toluene / benzene soluble
fractions that precipitate from petroleum when an excess (25 to 40 times) of n-heptane /
n-pentane is mixed with petroleum and waiting at least four hours before filtering.
Asphaltene precipitation causes fouling in the reservoir, in the well, in the pipeline and
in the oil production and processing facilities.
In this study, predictive methods and thermodynamic models to predict the hydrate and
asphalt free zone of hydrocarbon fluids were developed for field applications. The
topics studied included estimation of water content of natural gases in equilibrium with
the liquid water, ice and gas hydrates, prediction of hydrate inhibition effects of mixed
salt and organic inhibitor and finally modelling asphaltene precipitation conditions.
The results showed that the existing predictive methods show large deviations for
predicting the water content of natural gases at low temperature conditions and
therefore, new predictive tools were developed. Furthermore, the application of a
thermodynamic model was extended to mixed salt and chemical inhibitor commonly
used in petroleum production and transportation. This will provide a basis for the design of production and transportation facilities, particularly for deepwater
applications. A new correlation for predicting the hydrate inhibition effect of single and
mixed thermodynamicin hibitors was also developed.
A theoretical study was conducted to investigate asphaltene precipitation from
petroleum fluids during petroleum production and transportation. The results showed
that it is possible to use a polymer model namely the Scott-Magat theory combined with
an equation of state to predict asphaltene precipitation from reservoir fluids.