RHEOLOGY OF GAS-TO-LIQUID PRODUCTS: ALASKA NORTH SLOPE (ANS) CRUDE OIL AND THEIR BLENDS FOR TRANSPORTATION THROUGH THE TRANS ALASKA PIPELINE SYSTEM (TAPS)

It is projected that by the year 2015, ANS crude oil production will decline to such a level (200,000 to 400,000 bbl/day) that there will be a critical need for pumping additional liquid through the pipeline in order to maintain economic operation of the TAPS. The estimated proven and recoverable gas reserves of 38 trillion cubic feet (TCF) 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).

One of the proposed modes of transportation of the GTL products from ANS to market is by commingling them with crude oil as a single phase and pumping the mixture through the TAPS. This mode of transportation changes the properties of the GTL as well as the crude oil. This study therefore was to study the physical and chemical properties of GTL and its blends with crude oil, analyze the energy requirements for flowing the mixture through TAPS, and to determine the optimum blend ratio that would maximize the transportation economics. Four blends of GTL/crude oil mixture in the ratios of; 1:1; 1:2; 1:3; and 1:4; were prepared for their rheological evaluation and pressure drops at different temperature conditions.

The results of the analysis show that flow behavior of the GTL and GTL blends are temperature sensitive. Viscosity and density of the blends were found to decrease with increasing amount of GTL and increasing temperature. The optimum GTL/crude oil blend ratio of; 1:2.5 (28%: 72%) was determined to maximize the economics of commingled flow of GTL/crude oil mixture through the TAPS.