We introduce a reliable software package to simulate the long-term storage of CO2 injected into geological formations. Depleted oil fields and subsurface saline aquifers are examples of this type of formations. Our software (SubFlow) considers all the required parameters to determine whether a preselected injection site is in fact suitable for CO2 sequestration. SubFlow is an open-source, sustainable, and reliable software package that allows its users to model the transport of reactive chemical compounds in porous media. What makes SubFlow different from previously available tools is its numerical core (the module that simulates governing equations). We use mimetic discretization methods to attain accurate simulations without compromising the physical constraints inherent to the problem.