Relative Permeability Hysteresis and Capillary Trapping during CO2 EOR and Sequestration

Abstract

Residual or capillary trapping is an important mechanism of CO2 trapping in underground porous media. Recent experimental investigation has shown that relative permeability and capillary pressure are function of saturation changing direction or hysteresis phenomenon in addition to the saturation and hysteresis leads to irreversible change in relative permeability and capillary pressure curve. In this paper, an extended review was performed on the relative permeability hysteresis models. Moreover, an experimental investigation was conducted during CO2 injection as the non–wetting phase in carbonate rocks at pressure and temperature of 10.3 MPa and 60 ℃. In this study, the effects of absolute permeability of carbonate rock samples and CO2 injection strategy on hysteresis phenomenon in the CO2 residual trapping process were investigated. During first part of experiments, CO2 relative permeability was examined during CO2 injection and brine injection at constant rate of 0.2 cc/min as drainage and imbibition process for different absolute permeability of rock samples. During second part of experiments, CO2 trapping saturation was calculated during the continuous CO2 injection and CO2 Water Alternative Gas (WAG) injection. Results of first part of experiments showed that increasing of the absolute permeability leads to increasing initial and residual CO2 saturation at the end of drainage and imbibition process, respectively. Moreover, it was concluded that increasing rock permeability results in increasing of the hysteresis effect on the CO2 relative permeability. In the second part of experiments, results revealed that CO2 WAG injection strategy has higher CO2 residual saturation in compared to CO2 continuous injection at equal pore volume of injected CO2. The findings of this paper can be applied for investigating of CO2 sequestration projects in aquifers for improvements of CO2 residual trapping and studying the performance of capillary trapping as one of the main mechanisms of CO2 trapping.