Abstract Different injection methods have been already proposed by different researchers to improve the solubility of CO2 in formation brine. In this study a novel injection technique is presented, its aim being to cool down (liquefy) the supercritical CO2 injected in a wellbore through the use of downhole cooler equipment. Higher temperature CO2 entering the cooling equipment therefore exits with a lower temperature further downstream. If the temperature of the downhole, where CO2 is in contact with the formation brine, decreases to the lowest possible safe operational temperature, the consequence is an increase in the solubility of CO2 to the highest possible value for that pressure. The colder (liquid) CO2 has a higher solubility in brine, higher density and viscosity, which increases the security of the CO2 storage. Using this method to cool the supercritical CO2 down to a liquid phase increases its solubility at the wellbore, thereby eliminating the risk of a phase change or pressure and rate fluctuation in the liquid CO2 injection from the surface. Additionally the formation will have a lower pressure build-up because CO2 and brine are well mixed, and so less CO2 remains in the free phase.