Helping CO2 and brines to coexist

Interfacial fluid tension (IFT), just like wettability, is a factor known to influence the distribution and circulation of fluids in porous media. Consequently, in the context of geological CO₂ storage in deep saline aquifers, the brine/CO₂ IFT is a crucial factor determining not only the amounts of CO₂ that can be stored, but also the conditions for its injection into the underground environment.

However, data concerning this fluid system, in appropriate pressure and temperature conditions, are sparse, since the measurements required are lengthy and difficult to perform in a reliable and reproducible manner. It is for this reason that IFPEN has adapted pre-existing measurement hardware to the case of CO₂ and developed data interpretation software.

The measurement in question, known as the hanging (or rising) drop method, is based on:

• shape characterization of this drop,

• and makes it possible to determine interfacial tensions at up to 130°C and 350 bar.

In particular, measurements have been made between CO₂ and NaCl brines at variable concentrations, under different pressure and temperature conditions.

The influence of the salt's valency was also studied. While the IFT increases in a linear manner with the molar salt concentration, this increase in IFT is also related to the nature of the salt: it is twice as high with CaCl₂ than with NaCl.

In addition, it is observed that the total increase in IFT as a function of brine composition (NaCl + CaCl₂) is the sum of the two individual increments. The effect of the salts on the IFT is therefore additive.

These results have been successfully modeled, making interfacial tension a predictable parameter.

This study has made it possible to accurately predict for the first time the IFT for each aquifer considered, on the basis of:

• pressure,

• temperature,

• and concentration in various salts.
    
    

  
  
Scientific contact: michel.robin@ifpen.fr

 Published in Issue 17 of the information letter Science@ifpen - July 2014

Publications

• C. Chalbaud, M. Robin, J.-M .Lombard, F. Martin, P. Egermann, H. Bertin, Interfacial tension measurements and wettability evaluation for geological CO₂ storage. Advances in Water Resources 209, 32, 98–109.
  >> DOI:10.1016/j.advwatres.2008.10.012

• C.A. Aggelopoulos, M. Robin, O. Vizika, Interfacial tension between CO₂ and brine (NaCl + CaCl₂) at elevated pressures and temperatures: The additive effect of different salts. Advances in Water Resources, 2011, 34, 505–511.
  >> DOI:10.1016/j.advwatres.2011.01.007