Thermodynamics of Geofluids

Knowledge of the physicochemical (thermodynamic) properties of natural fluids is an essential basis to understand rock–water interaction and all its applications.

From direct observations and fluid inclusion studies we know that geofluids span a wide range of chemical compositions. Moreover, depending on the geological environment in which they occur, geofluids may be active at temperatures up to 1000 °C and at pressures up to several gigapascals. The extreme range of compositions, temperatures and pressures poses an enormous task for quantitative prediction of their properties.

We contribute to the existing knowledge base by measuring thermodynamic properties and by developing theoretical predictive models for geofluids relevant to our applied research projects.

All geofluids undergo phase transitions as a function of the pressure and temperature to which they are subjected within the Earth. Solid–liquid and liquid–vapour transitions are common examples. We need to know where in pressure–temperature–composition space such transitions occur, as they have a profound effect on rock–water interaction. We therefore map out the phase transitions for selected fluids at equilibrium conditions, using experimental and theoretical approaches.

The pressure and temperature under which a fluid of given composition occurs in the Earth determines all its physicochemical characteristics. Mathematical formulations of the relationships between pressure, temperature and the other thermodynamic properties (volume, density, enthalpy, entropy, free energy, etc.) are termed Equations of State. We have developed several Equations of State for fluids of selected compositions and pressure–temperature ranges.