The evolution of water chemical characteristics and their indicative function in CO2-enhanced water recovery

Abstract A monitoring method that uses the variation in water chemical characteristics of the deep storage layer was studied by a three-dimensional numerical model under the background of a CO 2 -enhanced water recovery (CO 2 -EWR) site in the Junggar Basin. The effect of water chemical characteristics on the migration of CO 2 in different phases and the transformations of major sequestered carbon minerals were determined from the resulting mechanism. The results show that the evolution of water chemical characteristics, such as pH, Ca 2+ and dissolved inorganic carbon (DIC), can effectively indicate the migration distance and time of dissolved CO 2 and supercritical CO 2 . The times corresponding to the turning points of the pH and DIC change curves at the monitoring points can plot the isochronal maps of dissolved and supercritical CO 2 migration, which can be used to quantitatively evaluate CO 2 migration in the reservoir. The changes of DIC and Ca 2+ can be used to infer the main carbon sequestration minerals: at the rapidly falling stage of Ca 2+ concentrate over time and the low concentrate of DIC, the main carbon sequestration mineral is calcite, and in other conditions is ankerite. Water chemical characteristics can identify the extent of injected CO 2 impact in the corresponding region. This paper provides an alternative method for monitoring CO 2 migration and conversion in different phases and determining the extent of injected CO 2 impact in a region by the type of sequestered carbon minerals.