How large is our CO2 storage capacity assessment error? Analyzing the magnitude of error in the effective capacity calculation propagated from uncertainties in the thermophysical conditions in the aquifer, the case of the Israeli Jurassic saline aquifer

Abstract

CO2 storage capacity assessment at a regional or country-size scale is one of the first tools for screening and ranking potential aquifers for deep geological storage. The estimated mass of the stored CO2 depends on the density of the supercritical CO2, which in turn is controlled by the aquifer hydrostatic pressure and temperature conditions. In this paper, we examine the magnitude of error in CO2 density and total storage capacity arising from uncertainties in subsurface temperature and pressure, and in particular from uncertainties in the surface temperature, geothermal gradient, depth of the piezometric-surface and the density of the formation water, that could propagate into the CO2 density and the total storage capacity calculations. Using the Israeli saline Jurassic aquifer as a case study, we establish the spatial distributions of the above temperature and hydrostatic pressure components and evaluate the errors using 'Monte Carlo' and 'one-factor-at-a-time' analyses. Our study shows that the depth of the piezometric-surface and the geothermal gradient have the strongest effect on the CO2 density and on the depth of the transition to supercritical CO2, whereas the influence of the surface temperature and the density of the formation water is rather small. As a side result of our study, we are showing that using average values or literature-derived values for the examined parameters, in the case of the Jurassic aquifer, over estimates the total storage capacity by 10% relative to the case where the spatial distribution of those parameters is used. While the analysis of the storage capacity was demonstrated here for the Jurassic saline aquifer in Israel, the conclusions concerning the effect of hydrostatic pressure and temperature uncertainties on the CO2 density and on the depth of the transition to supercritical CO2 are general and are especially important for relatively shallow or relatively thick aquifers in which the change in CO2 density with depth is large.