Gas Solubility Of Methane And Ethane In Cold Lake Bitumen At In Situ Conditions

Abstract

Abstract The vapour-liquid equilibrium properties of methane-Cold Lake bitumen and ethane-Cold Lake bitumen mixtures were measured using a modified Ruska rocking cell apparatus. Data measured at three isotherms for these two pseudo-binary systems 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, both of the equations of state can adequately represent the vapour liquid equilibrium properties of the two systems studied. Binary interaction coefficients of the modified Soove-Redlich-Kwong equation of state for the two systems were determined and correlated with temperature. Introduction Methane and ethane are commonly found in native Cold Lake oil sands bitumen, and are considered as possible additives for steam-based in situ bitumen recovery methods. Thus, the phase behaviour of methane-Cold Lake bitumen and ethane-Cold Lake bitumen mixtures under in situ conditions is important for reservoir engineers to determine the recovery of bitumen from Cold Lake deposits, as well as for process engineers to develop an adequate numerical simulation model Experimental data for these two pseudo-binary systems are not reported in the literature, and therefore one of the major objectives of this study was to measure their vapour-liquid equilibrium (VLE) properties. Experimental measurements are time-consuming and costly for these bitumen-containing systems. For the purpose of data reduction it is desirable to find methods which can predict their VLE properties with high accuracy. In this investigation, two cubic equations of state were selected to represent phase equilibrium properties. These are the modified Soave-Redlich-Kwong (MSRK) equation of state(1,3) and the Peng-Robinson (PR) equation of state (4,5). A commercially available "EQUI- PHASE" software package developed by DB Robinson and Associates was applied in vapour-liquid equilibrium calculations for the PR equation of state. Calculations were also performed with the PR equation of state using bitumen characterization parameters developed by Fu et al.(10) and binary interaction coefficients determined in this paper. The VLE properties measured in our laboratory are compared to the values calculated for the two gas-bitumen systems using both equations of state. Experimental Aspects Apparatus A schematic diagram of the experimental apparatus, which was verified for VLE measurements in a previous study(7), is shown in Figure 1. It 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 apparatus is the equilibrium cell which is located in a constant temperature bath container as shown in Figure 2. During measurements, the rocking cell is driven by a motor while a stirrer circulates the oil in the bath and keeps it homogeneous. Using this design, temperature was tested up to 423.2 K with an accuracy of ± 0.01 K, and pressure was tested up to 13.8 MPa with an accuracy of ± 1.0 kPa.