Viiscosity of Gas-saturated Bitumen

Abstract

Abstract The objective of this work was to measure the effect of dissolved carbon dioxide, methane and nitrogen on the viscosity of Athabasca bitumen. To accomplish these measurements, an apparatus was designed and built. The experimental results of gas-saturated bitumen show that carbon dioxide dramatically reduces the viscosity of bitumen particularly at low temperatures. The viscosity reduces with increasing pressure and temperature. The effect of pressure on lowering the viscosity is less prominent beyond a temperature of about 100 °C. The effect of dissolved methane on the viscosity is less dramatic but still significant. Dissolved nitrogen produced a negligible change in Viscosity. Introduction The viscosity of bitumen is a physical property, the knowledge of which is essential to solving the problems associated with the development of in-situ recovery of oil from oil sands deposits. The movement of high-viscosity crude would require extremely high and impractical pressure gradients. A viscosity reduction step is thus essential in transporting the bitumen. It has been well established that at reservoir pressures. dissolved gases have a substantial effect on the viscosity of crude oil. The most complete body of data on the effect of dissolved gases on the viscosity of crude oils is contained in the work published by Simon and Graue(1). However, their work was limited to crude oils with specific gravities of less than 0.95. For Athabasca bitumen with specific gravity greater than 1.00. the only substantial volume of data that has been published is that of Ward and Clark(2). Recently. Dealy(3) reported additional data on the rheological properties of bitumen. However, no data have been reported on the effect of dissolved gases on the viscosity of oil sand bitumen. Hence, the objective of this work was to measure the effect of dissolved nitrogen, carbon dioxide and methane on the viscosity of Athabasca bitumen. To accomplish this objective, an apparatus was designed and built to saturate the bitumen with gas and measure the resultant viscosity. Experimental Apparatus A schematic flow diagram of the apparatus is shown in Figure 1. The pump draws the bitumen along with its dissolved gas from the base of the mixing cell. The liquid is then pumped through a recycle line and a circulation line. The recycle line is used to supply bitumen to the top of the mixing cell, where a large surface area is provided for gas-liquid contact. The circulation line passes through the densitometer and the viscometer before returning to the-mixing cell. The division of flow in the two lines is controlled by means of the valve in the circulation line. The entire apparatus is placed in an electrically heated air bath to achieve a uniform temperature. A Contraves Model DC 44 viscometer, consisting of a torque meter and a driving motor, which was magnetically coupled to the measuring bob inside the flow-through cup, was used for viscosity measurements. The measuring cup was modified to reduce the hold-up volume of the viscometer. The viscometer calibration curves were supplied by the manufacturer.