Calibration of the Raman Analysis of Methane in H₂O-NaCl Solutions to 250°C Using Synthetic Fluid Inclusions

Damien Guillaume (damien.guillaume@g2r.u-nancy.fr), Jean Dubessy (jean.dubessy@g2r.u-nancy.fr), Stéphane Buschaert (stephane.buschaert@g2r.u-nancy.fr) & Jacques Pironon (jacques.pironon@g2r.u-nancy.fr)

UMR G2R (7566) Faculté des sciences - UHP, BP 239, 54506 Vandoeuvre lès Nancy, France

Methane is frequently associated with aqueous solutions from sedimentary basins. Concentration is usually below 0.2 molal and then presence of methane cannot be evidenced by microthermometry. However, the effect of low methane concentration have drastic consequences on the P-T projection of the L-V isopleth, and as a mater of fact on the interpretation of fluid inclusion trapping conditions in terms of pressure and temperature. The objective of this work is to calibrate the Raman analysis of methane at low concentrations using synthetic fluid inclusions in the H₂O-CH₄-NaCl system at different methane and sodium chloride molalities. Analytical data is compared with those obtained in water-methane system by Dubessy et al., 2000a. Synthetic fluid inclusions have been trapped in fluorine. This mineral was chosen because microcracks healing occurs in 4 weeks at 200°C. Pre-formation of the inclusion cavities was made using the laser ablation method described by Dubessy et al., 2000b. Samples were put inside the liquid phase coexisting with the vapour phase in a saturated vapour pressure autoclave. Bulk pressure was controlled by gas injection. Homogenisation temperature is then equal to experimental temperature. A specific software algorithm using the model of Duan et al. (1992) has been used to calculate the composition of the aqueous liquid phase coexisting with the vapour phase of the synthetic fluid inclusions below the homogenisation temperature. Calibration is based on the area ratio of the stretching band of methane (2917 cm^-1) on the stretching band of water (3000-4000 cm^-1) from spectra acquired with a Labram Dilor spectrometer. The intensity ratio of the Raman bands is well correlated with methane concentration and slopes of the regression curves depends on the sodium chloride concentration.

Duan Z, Moller N, Greenberg J & Weare JH, Geochim. Cosmochim. Acta, 56, 1451-1460, (1992).

Dubessy J, Buschaert S, Lamb W, Pironon J & Thiéry R, Chem. Geol., in press, (2000).

Dubessy J, Guillaume D, Buschaert S, Fabre C & Pironon J, Eur. J. Min., submitted

High Temperature and High Pressure Water Solubility in Hydrocarbons. A New Apparatus, Water Solubility in Ethylbenzene and Acetic Acid Effect

Damien Guillaume (damien.guillaume@g2r.u-nancy.fr)¹, Sergey Tkachenko (tsi@iem.ac.ru)², Jean Dubessy (jean.dubessy@g2r.u-nancy.fr)¹ & Jacques Pironon (jacques.pironon@g2r.u-nancy.fr)¹

¹ UMR G2R (7566) faculté des sciences - UHP, BP 239, 54506 Vandoeuvre lès Nancy, France

² IEM - Russian Academy of Science, Chernogolovka, Moscow District, 142432, Russia

Water solubility in hydrocarbons can be considered to be insignificant in the current oil fields conditions (T<100°C, P<500 bar), but oil prospecting turns toward deeper fields corresponding to higher temperatures (up to 200°C) and higher pressures (up to 1000 bar), and a priori water solubility in hydrocarbons can no more be neglected in those conditions. A new experimental device was developed for the study of water and hydrocarbons mutual solubilities in the Liquid-Liquid field, for pressure up to 1.5 kbar and temperatures up to 300°C. Sampling occurs at the experimental conditions to avoid condensation. We studied water solubility in ethylbenzene, acetic acid behavior and its effect on the water solubility. Water solubility was measured using the Karl Fisher method and acetic acid concentration in water and ethylbenzene was measured using FT-IR spectroscopy. The validity of our experimental and analytical procedures is confirmed by comparing our data with those obtained along the Liquid-Liquid-Vapor curve by Heidman et al., 1985. Experimental data show that at constant temperature, water solubility decreases slightly with increasing pressure. This pressure effect increases with increasing temperature. At constant pressure, water solubility increases with temperature according to an exponential law. Acetic acid concentrates strongly in the water-rich phase with a slow kinetics, and the pressure and temperature effects on water solubility are more pronounced in the presence of acetic acid. But this effect occurs when a really high acetic acid concentration is present in the water-rich phase, that is not realistic in natural conditions. This should mean that acetic acid will have an insignificant effect on water solubility in the natural fields conditions. The future is to study the effect of other organic acids or polar components that could fractionate into the hydrocarbon-rich phase.

Heidman JL, Tsonopoulos C, Brady CJ & Wilson GM, AIChE Journal, 31, 376-384, (1985).

Chemical Exchange between Carbonatite Melts and Mantle Lithologies Associated with Infiltration

Tahar Hammouda (taharh@ugcvax.dnet.gwdg.de)¹, Didier Laporte (laporte@opgc.uni-bpclermont.fr)² & Stephen Foley (sfoley@gwdg.de)³

¹ Geochemishes Institut, Goldschmidtstrasse 1, 37077 Göttingen, Germany

² Laboratoire Magmas et Volcans (CNRS), 5, rue Kessler, 63038 Clermont-Ferrand cedex, France

³ Petrologisches Institut, Goldschmidtstrasse 1, 37077 Göttingen, Germany

Since carbonatitic melts are often invoked as being responsible for mantle metasomatism, piston-cylinder experiments were designed in order to measure the rate of infiltration of such melts in mantle lithologies and to characterize chemical effects associated with such circulation. The experiments consisted in making infiltration couples by placing in contact a melt reservoir (carbonate) and a melt sink. The sink was prepared by sintering silicate minerals at high pressure and temperature and resulted in aggregates with no initial interconnected porosity.

A first series of experiments was performed using a synthetic dunite and a Na-carbonate saturated in olivine at run conditions (10 kbar and 1300°C). In those experiments the system was initially at chemical equilibrium and melt infiltration was driven only by the minimization of interfacial energies. Melt infiltration in the aggregate was very fast (2.5 mm in 1 hour). It obeyed a square root of time rate-law with chemical diffusion in the liquid as the rate-limiting process.

For a second series of experiments (10 kbar and 1000°C) we used a synthetic harzburgite (forsterite + enstatite) and a Ca-Na-carbonate melt doped in trace elements (U, Th, Pb, La, Gd, Yb). The melt was initially saturated in forsterite only. During infiltration a reaction occurred between the melt and the harzburgite in which enstatite was replaced by diopside. Such replacement textures have been described in mantle xenoliths where carbonatite metasomatism has been discussed. Electron microprobe and laser-ablation ICP-MS analyses of the phases present in the experimental samples will be used to discuss the chemical effects associated with carbonatite infiltration as well as the rate at which different components are redistributed between the participating phases.