UNDERGROUND-STORAGE OF CARBON-DIOXIDE

To prevent CO2 from entering the atmosphere, recovered CO2 MUSt be disposed of or stored. In this paper the underground injection of CO2 and the potential of underground storage are discussed. The recovered CO2 MUSt be injected into an underground reservoir through a well. The maximum flow rate greatly depends on the permeability of the matrix, the thickness of the reservoir, and the maximum allowable overpressure in the reservoir. Well flow rates may vary from 0.2 to 1.5 x 10(6) m(N)3 per day (400-3000 tonnes per day). If there is no flow, the pressure at the well-bottom is the sum of the well-head pressure and the pressure caused by the weight of the CO2 column. The pressure is reduced during injection by friction at the pipe wall. This effect is slight when pipes with a large enough diameter are used. With regular hydrostatic pressure gradients, extra compression at the well-head will often not be necessary. The density of the CO2 stored in the reservoir depends on the effective porosity, the depth of the reservoir, and the local geothermal and pressure gradient. The storage capacity of CO2 in aquifers depends not only on the density of the CO2, but also on the need of a structural trap and on the percentage of reservoir potentially available. The total storage capacity in natural gas fields is estimated at 500 to 1100 Gtonnes CO2. The storage capacity in aquifers is of the same order and possible much larger.