RAMAN SPECTRA OF AQUEOUS FLUID INCLUSIONS: EFFECT OF MINERAL BIREFRINGENCE AND METASTABILITY ON SALINITY MEASUREMENT

International audienceIntroduction: Crustal fluids play a major role in ore deposits, basin diagenesis and metamorphic reactions, among others. The knowledge of the chemical composition of individual fluid inclusions is essential for the understanding of past fluid transport and circulations. Microthermometry, by the observation of specific phase transitions as a function of temperature, is the general approach to determine salinity in aqueous fluid inclusions [1]. However in some cases, this method cannot be carried out because of, for instance, difficulties encountered in carrying optical observations, metastabil-ity, or if the thermodynamic system is not enough constraint. Besides, some minerals are highly cleavable, particularly carbonates, and consequently fluid inclusions might easily stretch, leak or decrepitate during freezing or heating on the heating-cooling stage, because of the volume expansion of the content with temperature. In replacement of microthermometry, salinity can be determined by Raman spectroscopy using a method based on the change of the shape of the water stretching vibration band with salinity. This change is due to the decrease of the strength of the hydrogen bonds in water by dissolved anions, often chloride [2,3]. An increase of the chloride concentration results in a decrease of the intensity of the OH stretching vibration band of water around 3200 cm-1. Different methods of treatment of the raw spectrum correlate the deformation of the OH stretching vibration band of water to chlorinity [4-9]. The Raman signal of water is also sensitive to the fluid density and the birefringence of the host crystal. Birefringence is critical in quartz and carbonates, and more generally in all highly birefringent minerals. Depending on the crystallographic orientation of the sample , the value obtained for salinity in quartz samples displayed variations higher than 50 % [5,7-9]. It has been observed that the " true " value is measured when the crystal is at its extinction position [6-9]. However, the optical phenomena behind the effect observed on the Raman spectra are not elucidated. Moreover, only the case of quartz was studied. Consequently, there is no general method at this time to determine salinity from the Raman signal of water in birefringent minerals. Met-astability may also affect the OH stretching vibration band of liquid water, the decrease of the fluid density affecting the strength of hydrogen bonds. Objectives: The purpose of the present study is to measure the effect of (i) metastability and (ii) mineral birefringence on the Raman spectra of water in aqueous fluid inclusions, in order to define a protocol to obtain accurate salinity measurement in any minerals, as an alternative to microthermometry

A raman spectroscopy study of the NI-MG kerolite solid solution: sensitivity of the O-H stretching vibrations to NI-MG substitution

International audienceIntroduction: The Ni-rich mineral phases forming the " garnierite " in the lateritic ore of the New Caledo-nian occurences are composed mainly in most cases by talc-like minerals, identified as kerolite. The Ni-Mg kerolite is a solid solution from Mg-kerolite to Ni-kero-lite (pimelite) with a structure close to the one of talc. The interlayer distance is of ~9.5 Å but with an excess of Mg in octahedral site, a relative deficit of Si in tetra-hedral site and a water content greater than the one in talc [1-4]. These minerals generally occur with a collo-morph texture, marked by a chemical zoning with growing bands characterized by alternative Ni/Mg ratio. However, the structure of these minerals is still not elucidated. Indeed, they form generally poor crystallized mixtures, in particular with interstratified serpentines [2], which makes their study complex. Moreover, the Ni-Mg distribution in octahedral site may be heterogeneous or form clusters at a nanometric scale [5]. The preliminary studies of Villanova-de-Benavent et al. [6] and Cathelineau et al. [7] showed a high sensitivity of the OH stretching and the low wavenumber region to the different mineral phases (talc, serpentine, kerolite). Raman spectroscopy seems thus to be a per-formant tool to easily determine the mineral phases in a garnierite sample

Uranyl interaction with the hydrated (0001) basal face of gibbsite: A combined theoretical and spectroscopic study

International audienceThe sorption of uranyl cations and water molecules on the basal (001) face of gibbsite was studied by combining vibrational and fluorescence spectroscopies together with density functional theory ͑DFT͒ computations. Both the calculated and experimental values of O–H bond lengths for the gibbsite bulk are in good agreement. In the second part, water sorption with this surface was studied to take into account the influence of hydration with respect to the uranyl adsorption. The computed water configurations agreed with previously published molecular dynamics studies. The uranyl adsorption in acidic media was followed by time-resolved laser-induced fluorescence spectroscopy and Raman spectrometry measurements. The existence of only one kind of adsorption site for the uranyl cation was then indicated in good agreement with the DFT calculations. The computation of the uranyl adsorption has been performed by means of a bidentate interaction with two surface oxygen atoms. The optimized structures displayed strong hydrogen bonds between the surface and the-yl oxygen of uranyl. The uranium-surface bond strength depends on the protonation state of the surface oxygen atoms. The calculated U – O surface bond lengths range between 2.1–2.2 and 2.6– 2.7 Å for the nonprotonated and protonated surface O atoms, respectively

Quantitative monitoring of dissolved gases in a flooded borehole: calibration of the analytical tools

Gas monitoring is a prerequisite to understanding the exchange, diffusion, and migration processes of natural gases within underground environments, which are involved in several applications such as geological sequestration of CO2. In this study, three different techniques (micro-GC, infrared, and Raman spectroscopies) were deployed on an experimental flooded borehole for monitoring purposes after CO2 injection. The aim was to develop a real-time chemical monitoring device to follow dissolved gas concentrations by measurements in water inside the borehole but also at the surface through a gas collection system in equilibrium with the borehole water. However, all three techniques must be calibrated to provide the most accurate quantitative data. For this, a first step of calibration in the laboratory was carried out. A new calibrations were required to determine partial pressure and/or concentrations of gases in water or in the gas collection system. For gas phase analysis, micro-GC, FTIR spectroscopy, and Raman spectroscopy were compared. New calibration of the micro-GC was done for CO2, CH4, and N2 with uncertainty from ±100 ppm to 1.5 mol% depending on the bulk concentration and the type of gas. The FTIR and Raman spectrometers were previously calibrated for CO2, and CO2, N2, O2, CH4, and H2O, respectively with an accuracy of 1–6% depending on concentration scale, gas and spectrometer. Dissolved CO2 in water was measured using a Raman spectrometer equipped with an immersion probe. The uncertainty on the predicted dissolved CO2 concentration and partial pressure was ±0.003 mol·kg−1 and ±0.05 bar, respectively

Role of Impurities on CO2 Injection: Experimental and Numerical Simulations of Thermodynamic Properties of Water-salt-gas Mixtures (CO2 + Co-injected Gases) Under Geological Storage Conditions

International audienceRole of impurities on CO 2 injection: experimental and numerical simulations of thermodynamic properties of water-salt-gas mixtures (CO 2 + co-injected gases) under geological storage conditions Abstract Regarding the hydrocarbon source and CO 2 capture processes, fuel gas from boilers may be accompanied by so-called "annex gases" which could be co-injected in a geological storage. These gases, such as SOx, NOx, or oxygen for instance, are likely to interact with reservoir fluids and rocks and well materials (casing and cement) and could potentially affect the safety of the storage. However, there are currently only few data on the behaviour of such gas mixtures, as well as on their chemical reactivity, especially in the presence of water. One reason for this lack comes from the difficulty in handling because of their dangerousness and their chemical reactivity. Therefore, the purpose of the Gaz Annexes was to develop new experimental and analytical protocols in order to acquire new thermodynamic data on these annex gases, in fine for predicting the behaviour of a geological storage of CO 2 + co-injected gases in the short, medium and long terms. This paper presents Gaz Annexes concerning acquisition of PVT experimental and pseudo-experimental data to adjust and validate thermodynamic models for water / gas / salts mixtures as well as the possible influence of SO 2 and NO on the geological storage of CO 2. The Gaz Annexes s new insights for the establishment of recommendations concerning acceptable content of annex gases

Raman spectra of gas-mixture in fluid inclusions: effect of quartz birefringence on composition measurement

International audienceThe composition of the gas mixture in fluid inclusions is one of the most important properties to obtain physical and chemical information of geofluids. Raman spectroscopy is a powerful tool for the quantitativeanalysis of the composition of the fluids trapped in inclusions. The peak area of each species is directly linked to concentration by its Raman scattering cross section (RSCS). However, previous studies showed that the peak area ratio of gases changed with gas mixture composition at the same P-T conditions 1,2 , indicating that RSCS is not a constant. Besides, previous studies proved the effect of host mineral birefringence onthe shape of the stretching vibration band of liquid water, having an impact on the quantitative determination of salinity 3 , but the influence on gas-mixture inclusions is still unknown. In this study, the Raman signals of CO2-CH4 and CO2-N2 in natural fluid inclusions in quartz were collected and compared to microthermometry data 4. It showed sinusoidal variations of the peak area ratio (ACH4/ACO2, ACO2/AN2) with the rotation of the samples on the microscope stage with a period of 45°. On the contrary, the area ratio of the two peaks of CO2 (n1380/n1280) and the Fermi diad split remained constant with sample rotation. These phenomena are probably linked to the birefringence of the host mineral as observed for liquid water 3

Advances in Fluid and Melt Inclusion Research – European Current Research On Fluid Inclusions ECROFI 2017 – Nancy, France

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Interpretation of the pressure-induced Raman frequency shift of the ν 1 stretching bands of CH 4 and N 2 within CH4-CO2 , N2-CO2 and CH4-N2 binary mixtures

International audienceThe relationships between the frequency shift of the v1 stretching bands of CH4 and N2 with pressure (or density) and composition has been previously provided in the literature as accurate empirical barometers and densimeters for the direct determination of the pressure or density of gas mixtures. However, the latter results still remain a pure description of the experimental data without any interpretation of the physical mechanisms hidden behind the variation trend of the observed peak position. The present paper is devoted to interpreting the origin of the pressure-induced vibrational frequency shifts of the v1 stretching bands of CH4 and N2 within CH4-CO2, N2-CO2 and CH4-N2 binary mixtures at the molecular scale. Two different theoretical models (i.e., the Lennard-Jones 6-12 potential approximation-LJ, and the generalized perturbed hardsphere fluid-PHF) are used to intuitively and qualitatively assess the variation trend as well as the magnitude of the frequency shift of the CH4 and N2 v1 bands for an in-depth understanding. Thereby, the contribution of the attractive and repulsive solvation-mean forces to the variation of the Raman frequency shift as a function of pressure and composition is assessed. A predictive model of the variation trend of the frequency shift of the CH4 v1 band as a function of pressure (up to 3000 bars), density and composition within CH4-N2 and CH4-CO2 binary mixtures is then provided

FRAnCIs calculation program with universal Raman calibration data for the determination of PVX properties of CO2–CH4–N2 and CH4–H2O–NaCl systems and their uncertainties

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Measuring mutual solubility in the H2O–CO2 system up to 200 bar and 100°C by in situ Raman spectroscopy

International audienceThe solubility control in the H2O–CO2system under high pressure is of prime interest in numerousgeochemical systems from hydrothermal fluids to CO2geological storage. However, the number of exper-imental data is scarce in the range of interest of geological storage, especially in the CO2-rich phase. A newexperimental device was built to measure mutual solubility in the CO2–H2O system without samplingby coupling a batch reactor with Raman immersion probes. The system was first calibrated by measuringthe solubility of CO2in water at 100◦C. The results were provided with an accuracy of a few % between40 bar and 200 bar and in agreement with other published experimental data sets and models. The lin-ear correlation between Raman peak intensity and CO2solubility in the aqueous phase was then usedto provide new experimental data of CO2solubility in water at 65◦C from 3 bar to 200 bar. The Ramandata of the CO2-rich phase or supercritical phase are compared to a thermodynamic models and the fewexperimental data available in literature to provide a new data set of H2O–CO2mutual solubility at 100◦Cand up to 200 bar