The Rheological Properties Of An Athabasca Bitumen And Some Bituminous Mixtures And Dispersions
Authors: Schramm Laurier L.L. , Kwak Jan C.T. 
Published: March 2010

An investigation was conducted into the rheological properties of an Athabasca bitumen, bitumen-naphtha mixtures, bituminous froth from the hot water flotation process, and froth-naphtha mixtures. These systems span a range of possible bituminous system components, bitumen) naphtha, air, solids and water, that are of interest in oil sand processing operations. It was found that bitumen itself is Newtonian in character (within the experimental uncertainty), having a viscosity of about 500 mPa.s at 80 °C. Bitumen viscosity is sensitive to temperature. For practical purposes, the temperature dependence of the A thabasca bitumen studied was found to be adequately represented by the Andrade equation.

The addition to bitumen of even a few per cent of naphtha was found to cause a dramatic lowering in the viscosity; the more so the lower Ole temperature. The dependence of mixture viscosities on naphtha content was found to be adequately represented by the Shu equations.

When other moieties are present in bitumen, its rheological character can become non-Newtonian and very complex. This was found to be the case for bituminous froth, which contained air, water and solids in addition to the bitumen. When bituminous froth was diluted with 10% or more naphtha, the (deaerated) mixture resembled very closely a bitumen-naphtha Mixture.

Introduction

Viscosity is an important property of bitumen. It is used, together with density, to distinguish bitumen from lighter and heavier hydrocarbons such as heavy oil and asphalt. As well as providing clues to its chemical composition and structure, the rheology of bitumen is of considerable practical importance. The Viscosity of bitumen in-place is so high, about 1 000 000 mPa,s at reservoir temperature in the Athabasca deposit, that the bitumen in oil sand is practically immobile. This makes the bitumen difficult to displace in attempts at in situ recovery(1,2), yet gives enough material strength to make surface oil sands mineable. Once mined, and when beneficiating oil sand, bitumen viscosity has some important influences.

In commercial oil sand mining operations, where the hot water notation process is used to extract bitumen, the bitumen viscosity must be reduced to help promote bitumen displacement from solids and subsequent aeration and flotation. This is done by raising the temperature to about 80 °C. In the commercial hot water flotation process the bituminous froth thus produced contains air and residual solids and water that must be removed before upgrading to synthetic crude oil. The latter components are removed by diluting the Froth with naphtha and then employing flotation/sedimentation of phases in centrifugal separators, These separations exploit the density difference between the solid (sludge) and hydrocarbon phases but large changes in the viscosity of the fluid can inhibit efficient separation by reducing the settling velocity. Throughout the processing steps, the flow properties are of obvious importance insofar as they determine how difficult it will be to handle and transport bituminous systems using pumps and pipelines. Here again, viscosity reduction can be achieved by changing the temperature or by adding a diluent.