Thermophysical properties of mixtures containing CO2 for applications in carbon storage and enhanced oil recovery

J. Trusler1

1Qatar Carbonates and Carbon Storage Research Centre (QCCSRC), Department of Chemical Engineering, Imperial College London, London, UK

Keywords: CO2 storage
property: phase behaviour, interfacial tension, viscosity
material: brine, oil

Understanding the phase behaviour and thermophysical properties of system containing carbon dioxide with hydrocarbons and/or water and salts is essential for the design of processes for both geological storage of CO2 and CO2-enhanced oil recovery (EOR). These important fields of engineering involve fluids under conditions of high pressure and over a wide range of temperatures within which a rich variety of phase behaviour is encountered, including the existence of multiple solid and liquid phases. Thermodynamic models are required that correctly capture these phenomena and permit reliable estimates to be made of phase properties and phase transitions. Since CO2 storage and CO2-EOR processes both involve less-well-studied regimes of temperature, pressure and composition, there is an need for new experimental measurements of phase behaviour and phase properties for the purposes of model optimisation and validation. In this paper, we present the results of new experimental measurements of phase behaviour, interfacial tension and viscosity for systems containing CO2 with hydrocarbons and/or water and salts at high pressures. The examples presented include the following: (a) the phase equilibria of ternary mixtures of the type (CO2 + n-alkane + water) in the regions of two- and three-phase coexistence; (b) the solubility of CO2 in brines, especially those containing divalent cations; (c) the interfacial tension of CO2 and brine; and (d) the viscosity of homogeneous mixtures of hydrocarbon + CO2. For phase behaviour we used both static-analytic and static-synthetic methods at pressures up to 20 MPa. The interfacial tension was measured by the pendant drop method, with pressures up to 50 MPa, and the viscosity was measured with a vibrating-wire instrument up to a pressure of 175 MPa. The experimental techniques will be described in detail and the results compared with available models. We would like to acknowledge that the QCCSRC is funded jointly by Qatar Petroleum, the Qatar Science & Technology Park, and Shell.

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