Influence of Capillary Pressure on Phase Equilibrium of Mixed CO2-water Injection into Geothermal Reservoirs Incl. Phase Appearance & Disappearance (SPE 153886)

In this article, the capillary pressure effect on the phase equilibrium of the CO2-water system is quantified. Our interest is in the capillary-pressure range between 0 and 100 bars for temperatures between 293 K and 358 K and pressures between 185 and 255 bars. For this purpose, we have implemented the capillary pressure effect in the PRSV equation of state. This makes it possible to determine the capillary-pressure effect on the CO2 storage capacity and energy recovery for CO2-water injection into geothermal reservoirs. We illustrate the process using a 2D model of the geothermal reservoir in the Delft Sandstone Member below the city of Delft (The Netherlands). Improved screening of injection conditions for optimal geothermal recovery and/or maximal CO2 storage. C"B" Capillary pressure reduces the CO2 solubility in water by less than 20%, whereas it increases the water solubility in the CO2-rich phase by less than 50%; C"B" Inclusion of the capillary pressure effect on the phase behavior does not significantly alter the capillary CO2-trapping mechanism (i.e., CO2 banks are mainly formed in highly permeable zones that are surrounded by less permeable zones), also heterogeneity still considerably weakens gravity effects; C"B" The frequent occurrence of evaporation and condensation, which is particularly effective close to the bubble point, substantially delays CO2 breakthrough and leads to a larger amount of useful-energy production and CO2 storage. C"B" However, for injected CO2 concentrations close to the bubble point, the effect of capillary pressure on the phase equilibrium can reduce both heat extraction and CO2 storage by 37%; for concentrations between 4% and 13%, the reduction is 10%. C"B" Based on simulations, we construct a plot of the recuperated useful energy versus the maximally stored CO2 for a variety of conditions including the capillary-pressure effect on phase behavior.