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When the Earth gives up its CO2

The carbon dioxide (CO2) often present in gas deposits sometimes occurs in high concentrations (>50%), which can be disadvantageous for exploitation of this resource.

Where naturally occurring CO2 has an organic origin (e.g. bacterial), it is recognizable in the carbon isotope signature. However, its many inorganic sources are difficult to identify. Nevertheless, their recognition is crucial in the process of targeting exploration.

One initial approach to identification is to characterize the associated "noble gases" (helium, argon, neon, etc.), either in terms of the origin of the gaseous mixture, or as process indicators of its migration. For more than 10 years, IFPEN has operated and expanded a laboratory dedicated to noble gas analysis. The work done by its researchers has shown that the CO2 contained in the Presalt deposits offshore Brazil originated in the continental mantle(1).

Another approach is based on modeling the reactions that form CO2 from the carbonated minerals of sediments(2). This modeling protocol makes it possible to demonstrate that, under the conditions prevailing at the bottom of some sedimentary basins (up to 500°C and 250 MPa), the CO2 originates from metamorphic changes in the terrestrial crust. It now forms an integral part of a prototype version of TemisFlow™, software used to quantify petroleum systems to assess their exploration potential.

Given the growing interest in natural gas and the deep geological resources, both these methodological options are promising. They open the way for a broader approach to other essential fluid components from deep beneath the earth (abiotic CH4, H2, H2S, N2, etc.).

 

Scientific contacts:  etienne.brosse@ifpen.fr  -  virgile.rouchon@ifpen.fr

Published in Issue 22 of the information letter Science@ifpen - September 2015

Publications

  • (1) V. Rouchon et al., Decoupling of the sub-basinal CO2 and He mantle fluxes as evidenced by intense CO2/3He fractionation of natural gases from Brazilian south Atlantic margin basins, Miner. Magazine, 2013.
    >> DOI: 10.1180/minmag.2013.077.5.18 (page 2088)
  • (2) X. Courtial et al., Electrolyte CPA equation of state for very high temperature and pressure reservoir and basin applications, Geoch. Cosmoch. Acta, 2014.
    >> DOI: 10.1016/j.gca.2014.07.028

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