In CO2 sequestration studies we usually see CO2 viscosity to be lower than that of brine. Is it possible that CO2 viscosity is higher in any study?
As you note, CO2 generally has a lower viscosity, and when mixed with either brine or oil, generally decreases the viscosity of the solution. If there were exceptions to this trend, I would expect they would occur at higher temperatures than are common in sequestration aquifers, i.e., greater than about 374 C. At this temperature, pure water would be supercritical (assuming pressures greater than 220 bar). Under these conditions, water viscosity behavior will differ significantly and may show the type of unexpected behavior you mention.
The CO2 viscosity is lower than that of brine; however, viscosity of brine-saturated with CO2 is higher than original brine. This causes instability and promotes convection. This Mechanism is described in the following papers:
1. Gholami, Yasin, Reza Azin, Rouhollah Fatehi, and Shahriar Osfouri, 2015, Suggesting a numerical pressure-decay method for determining CO2 diffusion coefficient in water, Journal of Molecular Liquids, vol. 211, pp. 31-39
2. Jafari Raad, Seyed Mostafa, Rooholla Fatehy, Reza Azin, Shahriar Osfouri, and Alireza Bahadori, 2015, Linear perturbation analysis of density change caused by dissolution of carbon dioxide in saline aqueous phase, Journal of Molecular Liquids, vol. 209, pp. 539-548
3. Azin, Reza, Seyed Mostafa Jafari Raad, and Shahriar Osfouri, 2015, Measurement of CO2 diffusivity in synthetic and saline aquifer solutions at reservoir conditions: the role of ion interactions, Heat and Mass Transfer Journal, vol. 51, No. 3, pp. 1587-1595
4. Gholami, Yasin, Reza Azin, Rouhollah Fatehi, Shahriar Osfouri, and Alireza Bahadori, 2015, Prediction of carbon dioxide dissolution in bulk water under isothermal pressure decay at different boundary conditions, Journal of Molecular Liquids, vol. 202, pp. 23-33
5. Azin, Reza, Seyed Mostafa Jafari Raad, Shahriar Osfouri, and Rooholla Fatehy, 2013, Onset of Instability in CO2 Sequestration into Saline Aquifer: Scaling Relationship and the Effect of Perturbed Boundary, Heat and Mass Transfer Journal, vol. 49, pp. 1603-1612
6. Azin, Reza, Mohammad Mahmoody, Seyed Mostafa Jafari Raad, and Shahriar Osfouri, 2013, Measurement and modeling of CO2 diffusion coefficient in Saline Aquifer at Reservoir Conditions, Central European Journal of Engineering, vol. 3, No. 4, pp. 585-594
All documents can be downloaded from my page on researchgate
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