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, Alaska North Slope (ANS)crude-oil production will decline to such a level (200,000 to 400,000 B/D) that there will be a critical need for pumping additional liquids through the pipeline to maintain economic operation of the Trans-Alaska Pipeline System (TAPS). The estimated proven and recoverable gas reserves of 38 trillion cubic feet (Tcf)on the ANS can be converted to a high-premium liquid product using gas-to-liquids (GTL) technology. The GTL product can be transported from the ANS to the southern port of Valdez, Alaska through the TAPS.One of the proposed modes of transportation of the GTL products from ANS to market is by commingling it with crude oil as asingle phase and pumping the mixture through the TAPS. This mode of transportation changes the properties of the GTL as well as the crude oil. The focus of this work, therefore, was to determine the physical and chemical properties of GTL and its blendswith ANS crude oil, analyze the energy requirements for flowing the mixture through TAPS, and determine the optimum blend ratioto 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 amounts ofGTL and increasing temperature. The optimum GTL/crude-oil blend ratio of 1:2.5 (28%:72%) was determined to take full advantage of the economics of commingled flow of GTL/crude-oil mixture through the TAPS.