FT‐IR measurements of petroleum fluid inclusions: methane, n‐alkanes and carbon dioxide quantitative analysis

Abstract

A recent advancement in petroleum geochemistry is to model fossil oil composition using microthermometric and volumetric data acquired from individual¯uid inclusion analysis. Fourier Transform Infrared (FT-IR) microspectroscopy can record compositional information related to gas (CH 4 and CO 2 ) and alkane contents of petroleum inclusions. In this study, a quantitative procedure for FT-IR microspectrometry has been developed to obtain, from individual¯uid inclusions, mol percentage concentrations of methane, alkanes and carbon dioxide as constraints to thermodynamic modelling. A petroleum inclusion in a sample from the Que  bec City Promontory nappe area was used as a standard to record a reference spectrum of methane. The analytical procedure is based on the measurement of CH 4 /alkane and CH 4 /CO 2 band area ratios. CH 4 /alkane infrared band area ratio is obtained after spectral subtraction of the reference methane spectrum. This area ratio, affected by absolute absorption intensities of methane, methyl and methylene, provides a molar CH 4 /alkane ratio. Methyl/methylene ratio (CH 2 /CH 3 ) ratio is obtained following procedures established in previous work. CO 2 /CH 4 concentration ratio is estimated from relative absolute absorption intensities. Application to natural inclusions from different environments shows good correlation between FT-IR quanti®cation and PIT (petroleum inclusion thermodynamic) modelling.

Synchrotron FTIR Hydrocarbon Fluid Inclusion Microanalysis Applied to Diagenetic History and Fluid Flow Reconstruction in Reservoir Appraisal

“…This could only be obtained by analysis and mapping at a microscopic scale. In the last decades, advances in molecular infrared microspectrometry a b, 1998Rankin et al, 1990;Pironon et Bares, 1990, Pironon et al, 2001) allow quantitative non destructive molecular analyses to be performed in a single fluid inclusion under a microscope. The size of the FI analyzed is currently restricted to the wavelength of incident beam (20 µm) when using a conventional source such as a Globar (Barres et al,1987).…”

“…We calculated the CH 3 /CH 2 ratio, the CO 2 and the CH 4 content (Guilhaumou et al, 1990a, Pironon et al, 2001) from the relative intensities of the absorbance spectra in the range 4000-2000 cm -1 (see details in appendix). Some uncertainties may be due to diffraction effects in the mineral matrix and associated components.…”

“…The CO 2 and CH 4 content and, in some cases, a molecular alkane content were calculated using their respective relative IR absorption intensities following the procedure of Pironon et al, 2001.…”

“…This value agrees with the value of C 9 previously calculated from FTIR spectroscopy, considering that during extraction (see appendix) we loose a part of the light fraction (Guilhaumou et al, 1990 a). Semi quantitative measurements using the Beer-Lambert law and an internal CH 4 calibration following the procedure of Pironon et al, (2001) lead to 42 mole percent CH 4 and 5 mole percent CO 2 as additional components.…”

In Situ Measurements of the H2o:co2 Ratio in Fluid Inclusions by Infrared Spectroscopy

“…Whereas this technique shows promise, it is not developed to the extent where Raman spectroscopy can be used to determine the H 2 O:CO 2 ratio of a fluid in an inclusion. Fourier transform infrared (FTIR) spectroscopy of fluid inclusions has primarily been applied to the analysis of petroleum in fluid inclusions (e.g., Pironon et al 2001), but has also been shown to be useful in the analysis of aqueous-carbonic fluid inclusions (e.g., Wopenka et al 1990, Brown 1992. In this study, we present FTIR results for aqueous-carbonic inclusions with a variety of compositions and molar volumes, determined at P-T conditions in the one-phase field.…”