Phase Equilibrium And Fluid Properties of Pembina Cardium Stock-tank Oil - Methane - Carbon Dioxide Sulphur- Dioxide Mixtures
Authors: Sayegh S.G. , Najman J. , Hlavacek B. 
Published: March 2010

Abstract
The phase equilibrium and fluid properties of a Pembina Car-dium stock-tank oil with methane carbon dioxide and sulphur dioxide have been measured at 45°C and 13.8 MPa. The properties measured are the compositions of the equilibrium phases, their densities and viscosities, and the oil swelling. Data points were taken along the saturated vapour-liquid and liquid-liquid surfaces, as well as in the one-phase region.
The experimental results have demonstrated that carbon dioxide – sulphur dioxide mixtures have the potential of being more effective enhanced oil recovery agents than either component alone because of improved miscibility characteristics, the ability to more closely match the density and viscosity of the oil and the increased oil swelling.
The volumetric data have been correlated using the corresponding states principle, and the viscosity data have been correlated using a free· volume theory.

INTRODUCTION
Carbon dioxide miscible flooding has become an increasingly popular enhanced oil recovery method. Recently, Stalkup(l) and Mungan(2) have presented reviews of the process. In the Petroleum Recovery Institute"s miscible flooding research project, the mechanism of the displacement process is being studied using carbon dioxide, sulphur dioxide, hydrocarbons, and their mixtures. Previous reports(3–6) on this work have dealt mainly with phase behaviour physical properties, and displacement studies of CO2 and SO2 with methane, n-pentane and n-hexadecane, the hydrocarbons being considered representative of crude oils. These studies have shown, among other things, that CO2/SO2 mixtures can be first-contact miscible with oil at conditions at which either CO2 or SO2 are immiscible. Furthermore, these mixtures can be formulated so that their viscosities and densities more closely match those of the oil. Thus, during a flood, the tendency for viscous fingering and gravity segregation would be decreased. Hence, CO2/SO2 mixtures have the potential of being more effective miscible flooding agents than either one alone.
As a further step, studies are now in progress using a Pembina Cardium stock-tank oil combined with CH4 to represent the reservoir crude. In the present paper, the results of the phase equilibrium and physical properties measurements are described and discussed. The system is considered to be a quaternary one: the "oil" being considered as one component, and CH4, CO2and SO2as the remaining three. Binary ternary and quaternary data are presented, and several correlations for the physical properties of such mixtures are considered.

Experimental Apparatus and Procedures
The experimental apparatus is shown schematically in Figure 1. It consists of two equilibrium cells "H" manufactured by Ruska Instrument Corporation, Model 2329-800-00. These have a maximum working temperature and pressure of 150°C and 65 MPa respectively. The two cells are rigidly held together in a frame "J", and their upper ports connected to a 19-m-Iong stainless steel coil "E", which is also attached to the frame. This tube has an internal diameter of 0.53 mm and is used for measuring viscosity, as will be explained below frame holding the cells and the coil is supported on a rocker assembly "K". During the mixing stage, the cell assembly is connected to an external electric motor and rocked.