Factors affecting CO2 storage capacity and efficiency with water withdrawal in shallow saline aquifers

Carbon sequestration in shallow aquifers can be facilitated by water withdrawal. The factors that optimize the injection/withdrawal balance to minimize potential environmental impacts have been studied, including reservoir size, well pattern, injection rate, reservoir heterogeneity, anisotropy ratio, and permeability sequence. The effects of these factors on CO₂ storage capacity and efficiency were studied using a compositional simulator Computer Modeling Group-General Equation of State Model, which modeled features including residual gas trapping, CO₂ solubility, and mineralization reactions. Two terms, storage efficiency and CO₂ relative breakthrough time, were introduced to better describe the problem. The simulation results show that simultaneous water withdrawal during CO₂ injection greatly improves CO₂ storage capacity and efficiency. A certain degree of heterogeneity or anisotropy benefits CO₂ storage. A high injection rate favors storage capacity, but reduces the storage efficiency and CO₂ breakthrough time, which in turn limits the total amount of CO₂ injected.