The simplest method for estimating storage capacityThe accumulated mass of CO2 that can be stored environmentally safely, i.e., without causing leakage of CO2 or native reservoir fluids or triggering geologic activity that has a negative impact on human health or the environment is the volumetric method. In this method, the capacity is estimated as a fraction of the calculated pore spaceSpace between rock or sediment grains that can contain fluids volume in the target storage(CO2) A process for retaining captured CO2, so that it does not reach the atmosphere formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it and structure(geology) Geological feature produced by the deformation of the Earth’s crust, such as a fold or a fault; a feature within a rock such as a fracture; or, more generally, the spatial arrangement of rocks, as constrained by an assumed realistic range of filling with supercritical(CO2) Conditions where carbon dioxide has some characteristics of a gas and some of a liquid CO2Carbon dioxide at the estimated reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids average temperature and pressure. At the other end of the complexity scale, one could estimate capacity using reservoirA subsurface body of rock with sufficient porosity and permeability to store and transmit fluids flow simulators and geomechanical analysis tools. As explained by Aarnes et al., 2010, this approach requires that the underground is explicitly represented in a three-dimensional digital geo-cellular model including the most relevant structural and petrophysical features, and the dynamic processes, e.g. injectionThe process of using pressure to force fluids down wells, fluid movement and spatial and temporal pressure responses. The capacity could then be estimated to reflect the maximum volume of CO2Carbon dioxide that can be injected without causing too large a pressure increase, CO2Carbon dioxide-spill at structural spill points, or migrationThe movement of fluids in reservoir rocks through other potential leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column pathways. Inferences about the potential for leakage(in CO2 storage) The escape of injected fluid from the storage formation to the atmosphere or water column can, in some cases, be made from regional knowledge, interpretation of seismic surveys or geomechanical modelling.