Abstract

Vapour-liquid equilibrium properties of methane-Cold lake bitumen and ethane-Cold lake bitumen mixtures were measured using a modified Ruska rocking cell apparatus. The measured data of these two pseudo-binary systems at three isotherms were used to develop a predicting method by means of equations of state. Two equations of state; the modified Soave-Redlich- Kwong and the Peng-Robinson, were chosen in this study. With an appropriate choice of bitumen characterization parameters and binary interaction coefficients, it is shown that both the equations of state can adequately represent the vapour liquid equilibrium properties of the two systems studied. Binary interaction coefficients of the modified Soave-Redlich-Kwong equation of state for the two systems were determined and correlated with temperature.

Introduction

Methane and ethane are commonly found in the native Cold Lake oil sands bitumen and these gases are considered as possible additives to the steam-based in situ bitumen recovery methods. Thus, the phase behaviour of the methane-Cold Lake bitumen and the ethane-Cold Lake bitumen mixtures under in situ conditions are important to reservoir engineers for determining the recovery of bitumen from the oil sand deposits as well as to process engineers for developing an adequate numerical simulation model. However, the experimental data for these systems are not reported in the literature. One of the major objectives of this study is to measure the vapour liquid equilibrium (VLE) properties of methane-ColdLake bitumen and ethane-Cold Lake bitumen mixtures.

Experimental measurements are time consuming and costly for the bitumen containing systems. For the purpose of data reduction, it is desirable to find methods which can predict the VLE properties for these systems with high accuracy. In this investigation, two cubic equations of state were selected for the purpose of representing phase equilibrium properties. These are the modified Soave-Redlich-Kwong (MSRK) equation of state1–3 and the Peng-Robinson (PR) equation of state4,5. A commercially available "EQUI-PHASE" software package developed by he DB Robinson & Associates66 was applied in vapour liquid quilibrium calculations for the PR equation of state. Calculations were also performed with PR equation of state using the bitumen characterization parameters developed by Fu et al.10 and binary interaction coefficients determined in this study.

The VLE properties measured in our laboratory compared to the calculated values for the two systems using both equations of state.

EXPERIMENTAL ASPECTS
Apparatus

A schematic diagram of the apparatus, which has been verified for VLE measurements in the previous study7, is shown in Figure 1. The apparatus consists of a charging and discharging unit, a constant temperature bath with a rocking equilibrium cell, and a sampling and analysis unit.

The heart of the whole apparatus is the equilibrium cell which is located in the constant temperature bath container as shown in Figure 2. During the measurement, the rocking cell, 4, is driven by a motor, 2. while the stirrer, L circulates the bath oil and keeps the oil in the tank homogeneous.

In this design, the temperature was tested up to 423.2 K with an accuracy of ±0.01 K and the pressure range tested was 13.8 MPa with an accuracy of ±1.0 KPa.

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