Issue 4, 2011

In situ gas monitoring in clay rocks: mathematical developments for CO2 and CH4 partial pressure determination under non-controlled pressure conditions using FT-IRspectrometry

Abstract

The quantification of dissolved gases in water at equilibrium with rock assemblages is very important for modelling the long-term behaviour of radioactive wastes and other materials in a deep geological disposal. This paper presents the mathematical development allowing to quantify the partial pressures of evolved gases from the rock that were collected from a borehole and transferred to a gas cell coupled to a low resolution FT-IR spectrometer. The areas of the different ν3 bands of CO2 between 2400 and 2220 cm−1 and the CH4 Q-branch between 3022 and 3002 cm−1 have been calculated using a peak integration method. It has been shown that the equation between the integrated area and the partial pressure for CH4 and CO2 for a spectral resolution of 1 cm−1 does not follow Beer–Lambert law and is dependent on the bulk pressure. A non-linear continuous calibration model has been developed for a range of bulk pressures from 0.9 to 1.4 bar, giving, for each gas, a relation between partial pressure and both integrated area and bulk pressure. Explored partial pressure ranges are between 0.3 and 4 mbar for CO2, and 0.3 and 12 mbar for CH4 with an equivalent optical path of 1 m. The relative root mean squared error of the prediction of the models is included between 1 and 3% in the explored pressure ranges for each gas.

Graphical abstract: In situ gas monitoring in clay rocks: mathematical developments for CO2 and CH4 partial pressure determination under non-controlled pressure conditions using FT-IR spectrometry

Article information

Article type
Paper
Submitted
15 Oct 2010
Accepted
07 Feb 2011
First published
16 Mar 2011

Anal. Methods, 2011,3, 888-895

In situ gas monitoring in clay rocks: mathematical developments for CO2 and CH4 partial pressure determination under non-controlled pressure conditions using FT-IR spectrometry

C. Cailteau, P. de Donato, J. Pironon, A. Vinsot, C. Garnier and O. Barres, Anal. Methods, 2011, 3, 888 DOI: 10.1039/C0AY00622J

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