Heavy-Oil Pipelines

Transporting heavy crude by pipeline consumes large amounts of mechanical energy, largely due to its viscosity, which is several hundred times that of a normal crude.

The movement of heavy crude creates a much greater frictional resistance in the pipeline to be compensated for by large line pipe and more pumping horsepower than is normally required for a light crude.

This resistance depends strongly on crude oil viscosity, which increases significantly as its temperature drops along the pipeline. Cooling of the crude occurs as it flows through the pipeline, losing its thermal energy to the surroundings.

Insulating or heat tracing the pipeline is effective for reducing the cooling rate and often is crucial for maintaining adequate flows. Such a design, however, will increase capital outlays and increase the costs of pipeline installation.

Where insulation and heat-tracing methods are impractical, consideration must be given to simplifying the design and minimizing the size of the pipeline.

In the meantime, the unique thermal dynamics benefits of the heavy crude must be explored, as they were for this study of a Venezuela heavy-oil pipeline.

This article will demonstrate how these benefits can be realized in heavy-crude pipeline projects.

A crude oil is usually classified as light if it has greater than 30° API gravity; a medium crude oil has a gravity of 22-30° API; while the gravity of a heavy crude oil is less than 22° API.

Vast amounts of heavy crude are produced in many parts of the world. Venezuela Orinoco heavy oil belt bitumen upgrades, Canadian Athabasca tar sands, and Labrador are some of the major suppliers of heavy crude.

Demand for heavy crude projects fell when oil prices dropped in 1998 and 1999 until the Organization of Petroleum Exporting Countries drastically cut crude oil production.

Since that cut, oil prices rose to more than $30/bbl in the summer of 2002. With stable, firm oil prices and increased world demand, interest in heavy-crude pipelines will soon revive.

The last heavy-crude pipeline under construction in 1997 in Venezuela was a 200 km (124 mile), 36-in. line to transport heavy crude from the Zuata region of the Orinoco Petroleum Belt of Venezuela to an export terminal near Barcelona.

The crude oil transported in this pipeline has a gravity of 9° to 15° API and a viscosity from 20, 000 to 1, 000 cst at standard conditions.

This heavy crude is blended with naphtha to a gravity of about 16° API and a manageable viscosity of about 400 cst. Blending heavy crude such as bitumen with naphtha produces a homogeneous mixture of Newtonian fluid characteristics.

The design capacity of this pipeline exceeds 500, 000 b/d. The addition of an intermediate pump station would increase this flow rate by more than 200, 000 b/d. the blended oil is pumped and heated to a typical temperature of 180° F. before entering the pipeline.