Régis Thiéry

Methane-bearing aqueous fluid inclusions: Raman analysis, thermodynamic modelling and application to petroleum basins

Abstract Calibration for the determination of the CH4/H2O ratio using Raman spectroscopy is carried out using synthetic fluid inclusions with 0 m NaCl. Spectra of the symmetric stretching band of methane (ν1,CH4), and the bending (ν2,H2O) and stretching (νS,H2O) bands of water were obtained in the aqueous phase co-existing with the vapour phase at variable temperatures from 25° to a few degrees above the homogenisation temperature. A software program, based on the model of Duan et al. (1992a) [Duan, Z., Moller, N., Greenberg, J.H., Weare, J.H. 1992a. The prediction of methane solubility in natural waters to high ionic strength from 0°C to 250°C and from 0 to 1600 bar. Geochim. Cosmochim. Acta, 56, 1451–1460.] has been developed to calculate the composition of the aqueous liquid phase co-existing with the vapour phase in the synthetic fluid inclusions. Application to natural samples from the Alwyn South area (North Sea) shows that Raman analyses permit discrimination between inclusion populations that are not recognised using only microthermometric measurements. These results provide important constraints on the P–T conditions of inclusion formation and suggest that oil migration occurred at fluid pressures of approximately 240 bars.

Individual characterization of petroleum fluid inclusions (composition and P-T trapping conditions) by microthermometry and confocal laser scanning microscopy : inferences from applied thermodynamics of oils

Abstract This paper proposes a new method to characterize individual oil-bearing fluid inclusions. It uses both the homogenisation temperatures measured by microthermometry, and the degree of gas bubble filling measured by confocal laser scanning microscopy, in conjunction with thermodynamic modelling for describing liquid–gas phase transitions and the volumetric behaviour of hydrocarbon mixtures. It is associated with a two-parameter (α, β) compositional model that describes the wide range of compositions of petroleums. We show that this method can give (1) useful estimations of the compositions and pressure–temperature entrapment conditions of oils in fluid inclusions, and (2) insights into the various processes that have affected these fluids either before entrapment (liquid–gas unmixing, gas leaching, mixing, etc.) or after (leakage, etc.).

Explosive Properties of Superheated Aqueous Solutions in Volcanic and Hydrothermal Systems

Superheated aqueous solutions in volcanic and hydrothermal environments are known to reequilibrate violently through explosive boilings and gas exsolutions. While these phenomena are purely kinetic problems in essence, the explosivity conditions of these demixion processes can be investigated by following a thermodynamic approach based on spinodal curves. In a first part, we recall briefly the concepts of mechanical and diffusion spinodals. Then, we propose to differentiate superspinodal (explosive) transformations from subspinodal (non-explosive) ones. Finally, a quantitative study of spinodal curves is attempted on the binary systems H2O-CO2 and H2O-NaCl with equations of state with solid theoretical basis. It is shown that dissolved gaseous components and electrolytes have an antagonist effect: dissolved volatiles tend to shift the superspinodal region towards lower temperatures, whereas electrolytes tend to extend the metastable field towards higher temperatures. This study may give some clues to understand the explosive destabilization conditions of aqueous solutions in phreatic, phreato-magmatic and hydrothermal eruptions