A novel renewable energy concept based on using supercritical CO2 as heat 
transmission fluid was proposed by Brown (2000). Pruess (2006) evaluated 
thermophysical properties and performed comparative numerical simulations to 
studying fluid dynamics, heat and mass transfer potentials of water and CO2 as 
heat transfer fluids in an engineered geothermal reservoir. He highlighted some 
advantages of using CO2 with respect to well bore hydraulics. Pruess and 
Azaroual (2006) extended previous analysis to include physicochemical 
interactions induced by CO2 between fluids and reservoir minerals. They 
concluded a potential of porosity increase and reservoir volume expansion. 
Simulation of multiphase reactive transport (CO2 in a porous carbonated rock 
initially saturated with water) illustrates existence of different zones featuring 
distinct reactive behaviour around the injection well (Andre et al., 2007). 
Supercritical CO2 reacts differently to CO2-saturated solution in each zone. 
First, it dissolves into the aqueous phase and increases both water acidity and 
mineral dissolution potential, favoring higher porosity. Next, hydraulic processes 
induced by supercritical CO2 injection are accompanied by a desiccation 
phenomenon of the porous medium. Irreducible water, entrapped in pores, 
sustains the increase in CO2 pressure. When the pressure is sufficiently high 
under a continuous dry (without water vapour) CO2 flux, an evaporation 
process starts leading to the precipitation of salts and other secondary minerals 
from capillary metastable water (Lassin et al., 2005). 
This new concept based on specific advantages thermophysical and 
physicochemical properties of CO2 as a heat transmission fluid integrating 
geochemical interactions and carbon geological storage constraints will be 
presented.

References 

André L., P. Audigane, M. Azaroual, A. Menjoz (2007). Energy Conversion 
Management (under press). 
Brown, D. Proceedings, Twenty-Fifth Workshop on Geothermal Reservoir 
Engineering, pp. 233–238, Stanford University, January 2000.
Fouillac, C., B. Sanjuan, S. Gentier, I. Czernichowski-Lauriol. Third Annual 
Conference on Carbon Capture and Sequestration, Alexandria, VA, May 3-6, 
2004.
Lassin A. M. Azaroual, L. Mercury (2005) Geochim. Cosmochim. Acta, Vol. 69, No. 
22, pp. 5187-5201.
Pruess K. (2006) Geothermics, Vol. 35, pp. 351-367.
Pruess, K., M. Azaroual. (2006) Thirty-First Workshop on Geothermal Reservoir 
Engineering, Stanford University, Stanford, CA, January 30 - February 1, 2006.

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