Experimental investigation on the transportation of commingled blends of gas-to-liquid (GTL) products and Alaskan heavy crude oil through the Trans-Alaska Pipeline System (TAPS)

Abstract

Heavy oil deposits in the West Sak and Ugnu formations are currently considered as potential resources to address the issue of declining oil production on Alaska's North Slope (ANS). Similarly, an estimated proven and recoverable ANS gas reserve of 38 trillion cubic feet (TCF) can be converted to high premium Gas-to-Liquid products which may be commingled with Alaskan heavy oil products. These commingled blends of GTL and Alaska heavy oil can be transported through the Trans Alaska Pipeline System (TAPS). The primary operational issues that could affect the transportation of these fluids through TAPS are: pump ability of the heavy oil, cold restart following a prolonged shut down, and solid deposition in the pipeline. Since TAPS was originally designed to carry light to medium, low viscosity crude oil, transporting heavy or viscous oil may cause problems with the overall hydraulics. In this study, ANS crude oil was distilled and the heavy fraction cuts (~18° API gravity) were commingled with ANS crude oil and GTL samples for evaluation. Density and viscosity results showed that addition of GTL significantly reduced heavy oil viscosity to present TAPS conditions. However, solid deposition was observed to be a potential problem.