CO2-plume geothermal processes: A parametric study of salt precipitation influenced by capillary-driven backflow

Utilizing CO2-plume geothermal systems allows both carbon dioxide storage (about 12% of the injected CO2 - 1.4 Mt - in this study) and geothermal heat exploitation by producing hot fluid. However, the commercial and technical feasibility aspects of such systems are major challenges to address. Salt precipitation is a common phenomenon that governs near-well damage and pressure build-up. Although various governing parameters affect the amount and the extent of salt precipitation, capillary-driven backflow is considered in a recent review paper by Miri and Hellevang (2016) as a key mechanism that determines regimes of salt precipitation. As a result, a comprehensive sensitivity analysis is performed on a wide range of parameters, including relative permeability and capillary pressure curves; injection flow rate and temperature; and reservoir's initial salinity, porosity, and temperature to underpin the role of capillary pressure and capillary-driven backflow on salt precipitation. Moreover, a backflow extent parameter (BEP) is defined, through which the brine backflow velocity profile is linked to salt precipitation. It is observed that capillary backflow significantly influences the pattern and enhances near-well salt precipitation. Also BEP is found to have a semi-linear relation to the amount of the precipitated salt. Also, increase in brine salinity (up to a critical value similar to 175, 000 ppm for our simulations) resulted in a significant reduction in reservoir porosity and permeability surrounding the injection well. In addition, the imposed required pumping power is analyzed, and an average (over all salinities) 20% increase of pumping power is required to keep the injection rate constant at the present study.