The effects of quartz content on the formation of residual water in a brine-CO2-quartz system: An experimental study

Geo-sequestration of CO2 in deep saline aquifers is achieved by injecting CO2 into the aquifers and displacing brine. The residual water formed during the drainage process has a strong influence on traps of residual-gas. Moreover, in the context of CO2 geological storage, the characteristics of the brine-CO2-quartz system directly impact residual trapping capacities. We conducted experiments to investigate the influence of quartz content in the rocks on the formation of residual water and how much of this residual water remains after CO2 is injected. Three sandstone core samples were all saturated with 35 g/L NaCl brine. Supercritical CO2 was injected into the samples at aquifer temperature and pressure and the displaced water and water-gas mixtures were collected and measured. The results show that the irreducible water saturation was lower with higher quartz content in the rock core. The permeability of rock cores can only influence the drainage efficiency; it does not have a decisive impact on the irreducible water saturation. Based on drainage flow rates, the process of drainage can be divided into three stages termed: Pushing Drainage, Portable Drainage and Dissolved Drainage. This terminology differs slightly from previous time-frame characterizations. Note that we have used a capillary model to interpret the mechanisms that characterize the three stages in these experiments.