Phase behavior analysis of gas-to-liquid (GTL) products for transportation through Trans Alaska Pipeline System

Abstract

The natural gas reserves on the North Slope of Alaska can be converted to a high premium liquid product using the Gas-to-Liquids (GTL) technology. The GTL product can be transported from the North Slope of Alaska to the southern port of Alaska through the Trans Alaska Pipeline system (TAPS). In this study, experimental work done in the laboratory to determine the phase behavior and fluid properties of the GTL products and their blends with North Slope crude oil has been presented. To transport the fluid, it becomes necessary to investigate the phase behavior of the fluid at pipeline conditions. Bubble point measurements were conducted to determine, in what phase the TAPS crude oil and GTL blends will exist when being transported through TAPS. Density and viscosity measurements were done to facilitate the fluid property modeling at elevated pressure conditions. The bubble point obtained using the DB Robinson's phase behavior apparatus were used for verifying the accuracy of the Soave-Redlich-Kwong (SRK) and the Peng-Robinson (PR) Equation of State (EOS) for predicting the phase behavior of GTL, TAPS crude and their blends. The results indicate that the GTL and GTL/crude oil blends will always exist as a single-phase liquid, hence two phase problems associated with transportation of the GTL can be ignored. The PR and the SRK equation of state can be used for modeling the phase behavior of the commingled fluid through TAPS. The Peng-Robinson equation of state and the Pederson principle of corresponding state have been used for modeling the density and viscosity of the GTL and GTL/crude oil blends.